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hair and feet of animals prior to moving.
• Control
weeds in feed and bedding grounds. Many weed seeds pass through the animal's digestive tract intact and viable (See Table 4)
76
Use only well rotted manure. Storage should generally be four to five months. In dry years, storage should be longer unless you perio • dically
moisten the manure pile. Decomposition can be hastened by adding nitrogen fertilizer and turning the pile a few times. • Immediately reseed soil disturbances. • Practise Total Farm Weed Control. Clean fencelines, irrigation ditches, stockyards, farm roads, or any annual weed seed nursery to prevent spread by natural or other means.
77
Table 9 Weed
Horses
Cattle
Swine
Sheep
Quackgrass Redroot pigweed Common Yarrow Cheatgrass Lamb's-quarters Ox-eye daisy Canada thistle Wild carrot Cypress spurge Dog mustard Wild buckwheat Lady's-thumb Common purslane Broadleaved plantain Curly dock Tall buttercup Wild radish Green foxtail Nightflowering catchfly Corn spurry Chickweed Dandelion Common mullein
+ + + + + + +
+ + + + + +
+ + + + + + +
+ + + + + + + -
-
-
+
+
-
+
+ + +
+ + +
+ +
+ +
+
+
+
+
+
+
+ + +
+ + +
+ -
+ +
78
+ Germinated after passing through animal - Did not germinate PHYSICAL STRATEGIES Tillage Soil is the principle factor of the environment that the farmer manipulates in crop production. Soil tillage enables the farmer to attack many weed survival mechanisms. For annual weeds, the tillage objective is to prevent seed production and deplete current seed reserves in the soil. This is accomplished by encouraging weed seeds to germinate, then subsequently killing them. With perennials, destruction of the underground parts is sought, as well as the prevention of seed production and reduction of seed reserves. Tillage kills weeds by: • Burial
of the entire plant. If complete burial is not accomplished and a small portion of the plant is exposed, life may continue. Burial is usually only effective with seedlings. • Depleting food reserves. This is accomplished by repeatedly removing top growth whenever it reaches sufficient size. Food manufacture can be halted by cutting off the plant tops or burning them. Tillage that breaks the underground parts into pieces is also very effective. This creates more growing points to use up food, and hastens food depletion. • Exposure of underground parts to frost. The roots of most plants are killed when left on or near the soil surface during freezing temperatures. Fall cultivation followed by spring-tooth harrowing brings underground parts to the surface. • Exposure of root systems to drying. If many roots remain under moist soil, growth will continue, therefore tillage must be thorough, with the plants fully exposed on the soil surface.
79
• Encouraging
rotting of underground parts. Physical injury to underground parts due to tillage enables the entry of decay causing bacteria.
Spring Tillage: Don't till deeper than four inches. Deep tillage buries weed seeds and temporarily minimizes weed problems, but subsequent tillage will bring these seeds to the surface again. Seeds in the soil can germinate many years after burial - sometimes for up to 40 years or more. Tillage should be designed to catch the first flush of weeds prior to sowing the crop. In moister areas tillage may be designed to control more than one flush of weeds prior to seeding.
80
dock_curly_young
dock_curly_plant
dock_broadleaf
dandelion_seedling
81
dandelion_flower
dandelion.plant
daisy.ox-eye.plant
daisy.ox-eye.flower
82
Cupplant
cudweed.low.plant
cucumber_bur_young
cucumber_bur_plants
83
crabgrass_smooth
crabgrass_hairy_
cowwheat.plant
cowwheat.flower.
84
Cornflower
coneflower_purple
coneflower_cutleaf
coneflower
85
compassplant
coltsfoot.plants
cogongrass.
cocklebur_common_plant
86
Post-seeding tillage, if practical, should be done in dry, warm, sunny and perhaps windy conditions so that weed seedlings once disturbed are not able to transplant themselves. Fall Tillage:Tillage after harvest can effectively kill biennials and suppress perennials. Under suitable conditions in the fall, weed germination may be stimulated making the new seedlings susceptible to frost kill. Hand Weeding Annual and biennial weeds and non-creeping perennials can be destroyed by simply pulling them out. This is best done when the soil is moist and before seed is produced. This is only practical of course for small patches or individual plants. Mowing When weeds are too numerous to hand pull, too large to effectively destroy by cultivation, or in an area where cultivation is impractical or impossible, they can be destroyed by mowing. This should be done before they produce seed and as close to the ground as possible. Perennial weeds usually require several cuttings before the food reserves in the roots are exhausted. If only a single cutting can be made, the best time is just prior to blooming because (1) the reserve food supply in the roots is at its lowest level, and (2) viable seed is often produced just after blooming. Perennial sow-thistle begins producing viable seed only three days after blooming and after nine days, 73 percent of the seeds may be viable.
87
Grazing The repeated removal of weed top growth by grazing animals, like close mowing, prevents seed formation and gradually weakens underground parts. Horses, sheep, goats, hogs and cattle are effective in destroying many weeds, if they are properly managed. Grazing animals should not be turned into pastures too early in the spring before the pasture grasses have made good growth. If grazing is permitted too early, the grasses do not develop a competitive stand and the weeds tend to take over. Ideally, pasture should be subdivided into two or more lots. This permits pasture areas to be grazed in rotation. If managed correctly, more weeds will be cleaned up than if livestock are allowed to roam over a large area and choose the more desirable forage, leaving the weeds to become rank, unpalatable, and over a period of time the dominant pasture plants. By rotating the pastures, desirable forage is encouraged during its rest period and results in healthier competitive pasture plants. Rotation also permits herbicide treatment with a safety margin, enabling the breakdown of the chemical before returning the pasture to grazing. Burning In situations when seed production has already occurred, some of the seeds can be destroyed by burning. The effectiveness of burning depends on the duration and intensity of heat produced, plus the maturity and location of the seeds. Mature, dry seeds are more heat resistant than green seeds, which have a high moisture content. Although intense heat will destroy most seeds remaining in plant heads, only a relatively small number of seeds on or below the soil surface can be destroyed by burning surface trash. Burning weeds over an extended area destroys valuable surface trash that would normally be returned to the soil through decay or cultivation.
88
In most farming operations, the most appropriate use of burning would be to selectively burn patches of weeds that have headed out by using a large propane torch. The flame can be directed at the mature heads of the weeds and the undesirable side effects of burning can be largely avoided. This is one of the few effective methods of preventing the dissemination of airborne seeds like Canada thistle, sow thistle, etc. Row crop producers sometimes use flaming machines which selectively burn weed top growth between the rows of specialty crops. Mulching The principle of mulching is to exclude light from the tops of the weeds until the reserve food supply in the roots is depleted and the weeds starve. Mulches include clean straw, hay or manure, tar paper, sawdust and black plastic. Black plastic is very effective. When the vegetation under the mulch has been destroyed, the resultant bare patch must be reseeded with competitive vegetation to prevent new weed introductions. CULTURAL STRATEGIES Cultural control uses plant competition or cropping practices to suppress weeds, either through use of smother or competitive crops and crop rotation. Crop Rotations Certain groups of weeds are almost always associated with specific crop rotations because: • They
are able to compete well with that crop. are not destroyed by the herbicides and cultivations that normally accompany production of the crop.
• They
89
Continuous cropping to small grains, for example, results in an increase in weed populations, chiefly annuals. Perennial forage crop plantings or permanent pastures favour development of perennial weeds like Canada thistle and quackgrass. Repeated plantings of the same crop favour the development of insects and diseases which result in weak or patchy stands which are easily invaded by weeds. Summer annual weeds in grain plantings can be reduced by rotating to perennial forages or to row crop production where practical. Once perennial forage crops are established and well managed, cutting for hay will suppress annual and perennial weeds, and eventually the competition will eliminate annual weeds. Fall seeded crops such as fall rye or winter wheat provide increased early season competition to seedling weeds and the early harvest enables a partial summer fallow for the balance of the season. Despite rotating crops, intensive summer fallow is often the only cultural alternative on land severely infested with perennial weeds such as Canada thistle and quackgrass. Summer fallow is designed to suppress growth, prevent seed production, deplete seed reserves in the soil and starve weed roots. Plant Competition The use of plant competition is one of the cheapest and most useful general weed control practices available to all farmers. Competition uses one of nature's oldest laws - survival of the fittest. Weeds are strong competitors by nature. If not, they would fail nature's survival tests. Certain weeds that can best compete under a certain set of circumstances always tend to dominate.
90
As mentioned earlier, weeds compete with crop plants for light, soil moisture, soil nutrients, carbon dioxide, and space. For example, one mustard plant from germination to maturity uses twice as much nitrogen and phosphorus, four times as much potassium, and four times as much water as one well developed oat plant. As a general rule, for every pound of weed growth produced, about one less pound of crop growth is produced. Usually, early weed competition reduces crop yield far greater than late season weed growth. It naturally follows then, that early weed control is exceptionally important. Late season weed growth may not seriously reduce yields, but it can make harvesting difficult, lower crop quality, and add to the reservoir of weed seeds in the soil. Crop Establishment As a general rule, the first plants to germinate and emerge in an area tend to exclude all others. Therefore, it is critical when considering plant competition as a weed management tool to establish a vigorous dense crop. Important factors that affect germination and emergence include the viability of the crop seed (percent germination), soil temperature, availability of moisture, and physical resistance to seeding emergence by the soil. These factors are influenced by the soil type, physical condition of the soil, depth of planting, the firmness of soil around the seed, the degree of soil compaction above the seed, and the formation of surface crusts after planting. The final stand will also be influenced by post-emergent stress due to weeds, diseases, insects and adverse weather conditions. Crop germination, if planting has been correctly done, is generally rapid and predictable. If pre-seeding weed growth has been killed, at least a temporary advantage has been gained for the crop. This initial advantage can be lost however, if effective post-seeding herbicide application or tillage is not undertaken to control late emerging weeds.
91
FACTORS LEADING TO MAXIMUM CROP COMPETITION Prepare Good Seedbed - Stale Seedbed Technique: A good seedbed is prepared, but no seeds are planted. After a good growth of weeds have emerged, they are killed using a non-selective herbicide with no residual effect in the soil. The crop is then planted with as little disturbance of the soil as possible to avoid bringing fresh weed seeds to the surface. This technique controls the all important first flush of weeds. Rate of Seeding: Heavier seeding rates can be used to reduce weed competition in areas where sufficient moisture is available. This applies to seeding completed at the regular time, as well as in a delayed seeding program. The recommended heavy seeding rate varies from 25 to 100 percent more seed, depending on the crop and the location. However, it should be remembered that heavy seeding rates should be used together with other cultural and chemical control measures to be most effective. Date of Seeding: Different weeds have different preferences for germination. Weeds such as many of the mustards and wild oats germinate best in cool conditions and are therefore more of a problem in early sown crops. Redroot pigweed and green foxtail prefer warmer soils and therefore germinate later. Late seeding allows for tillage or pre-seeding herbicide control of early germinating weeds. Early seeding results in crop competition with later germinating weed species. By varying crop seeding dates weeds have difficulty adapting. Crop Variety: It is important to choose a variety of crop plant that is well adapted to local conditions of soil, water, climate and disease resistance.
92
Fertilization: The fertility of the soil affects both the vigour of crop plants and the vigour of weeds. Many weeds can utilize fertilizers as well as or better than crop plants. Nevertheless, if most of the weeds are suppressed or killed by tillage or herbicides, the extra vigour given to the crop by fertilizers will make them better competitors. Placement of the fertilizer in the crop rows has an advantage over broadcast fertilization because most of the fertilizer is directly available to the crop. Smother Crops: A smother crop is defined as a thick stand of rapidly growing crop that competes with weeds to such an extent that their top growth is drastically suppressed and their roots are severely weakened. Alfalfa, when it becomes well established, is an excellent smother crop. Its extensive root system enables it to compete with most weeds for water, and its dense top growth smothers new weed growth. The principle value of smother crops in weed control is that they severely weaken the underground parts so that weeds are readily killed by the cultivation that follows. Soil - Water Relationships: Water relations, particularly the quantity of rainfall and its distribution, are critical to growth. Soil type, texture and the height of the water table are also important. Most land cropped with cereals and vegetables is sufficiently drained that any improvement of the overall drainage would have little effect on weeds. Soil Reaction: Certain weeds tend to be associated with alkaline and acid soils. For example, wild barley and arrowgrass are more prevalent on alkaline soils. Wild oats do better on acid soils than most cereals. Amending soil reaction is suggested where indicator weed species prevail.
93
Limitations of Competition The most that should be expected is suppression of weed growth and a measure of practical control. Competition is a good secondary tool and is most effective when used in combination with other control strategies. BIOLOGICAL STRATEGIES Biological control refers to the use of natural agents such as insects, nematodes, fungi, viruses or fish for the control of weeds. In some instances, grazing animals can be used to harvest and stress noxious weeds. Sheep have been used to successfully to control tansy ragwort and goats and sheep can be used to control leafy spurge. There have been a number of successes using biocontrol and this method is receiving increased attention in British Columbia. The objective in biocontrol is never eradication; it is reduction of a weed's density to non-economic levels. Biocontrol begins by first looking at the natural enemies of a particular weed in its native country. Most of our weeds are native to Europe and Asia. When a suitable control agent has been found, it is screened by the International Institute For Biocontrol in Switzerland in conjunction with Agriculture and Agri-food Canada, Biocontrol Section, Lethbridge, Alberta. Screening can take more than five years to complete as feeding trials must be performed to ensure the agent is specific only to the target weed and not to crops and other desirable plants as well. The usual procedure, where insects are being considered, is to starve the bug, then offer them a variety of host plants as potential food. This is done to ensure that the insects would rather die than eat a non-target plant. When screening is complete, the insects are increased and permission to release is received from North American Federal Governments. As a further precaution, new agents are not released to 94
B.C. until a review and approval is obtained from the British Columbia Plant Protection Advisory Council. Most biocontrol work to date has involved the use of insects. These act in many ways, including defoliation of the plant, boring into roots and eating seed, or forming galls in the seed head to prevent seed formation. Biocontrol is a self-regulating type of weed control. That is, as the weed host increases so does the insect population. As the weed population decreases due to the insect, the insect population also decreases. A balance is hopefully attained where the weed and insect populations are held at a low level. Biocontrol is designed for the most part for noncultivated lands where biennial or perennial weeds are troublesome. Cultivated lands are not usually suitable as the weed food source for the biotic agent is removed periodically. An exception is the recent discovery of a specific fungus disease which controls round-leaved mallow in wheat fields. Biocontrol Status In B.C. - 1998 To date 57 bioagents have been released on 20 weed species on over 4000 sites in British Columbia. Once approved for field release in B.C. the following procedure ensures provincial distribution: 1. first field release under controlled conditions. The majority of new agents are propagated at facilities maintained by the Ministry of Forests at Kamloops. Purpose - propagate agents.
95
2. caged release of offspring from propagated agents to protected areas. Purpose: to increase agents under diverse ecological conditions. 3. provincial distribution over the weeds range. Weed Species Targeted For Biocontrol Research In B.C. Sow Thistle Tansy ragwort Canada Thistle Sulphur cinquefoil St. Johnswort Puncturevine Hound's-tongue Plumeless Thistle
Scentless Chamomile Knapweed complex Nodding Thistle Bull Thistle Leafy Spurge Dalmation Toadflax Yellow Toadflax Purple Loosestrife Rush Skeletonweed
Biological weed control is the ultimate in controlling undesirable vegetation as it uses natural forces in a way which will least upset the environment. Much experimentation and screening has yet to be done, however, before this method can be used to the exclusion of alternate control measures for many of our noxious weedy plants. CHEMICAL STRATEGIES Man began to experiment with chemicals to control weeds in the 19th Century but it was the phenomenal success of 2,4-D, introduced commercially in 1946, that launched the present era of herbicides. It is important to understand a few basics of herbicides and their use so that they might be used effectively as a component of an integrated weed management program.
96
cockle_cow
cockle_corn_plant
cockle.white.flowe
clover_yellow_flowerplant
97
clover_white
clover_red
clover_prairie_bush
clover.rabbit-foot.plant
98
clover.large-hop.plant.
cinquefoil.three-toothed.plant
cinquefoil
chicory_plant
99
chickweed_mouseear_plant
chickweed_common_plant
chickweed_mouseear_flower
chickweed_common_flower
100
chickweed.mouse-eared.flowers
cherry.flower
cheatgrass
cheatgrass
101
cattail
catnip_young
catnip_plant
catnip_flower
102
catchweed_bedstraw
castorbean_plant
carpetweed
carpetweed
103
cardinal_flower_flowerWop
canker-root.plant
canker-root.flower.
canarygrass_reed
104
CHAPTER 4
CERTAIN EXPERIMENTS TO STUDY HERBICIDES CHARACTERS 1. PHOTO DECOMPOSITION OF HERBICIDES Background Photo decomposition usually happens in the field under moisture deficit conditions. This decomposition by light begins when the herbicide molecule absorbs light energy resulting in the excitation of the electrons and consequently breakage or formation of chemical bonds. Materials and Methods a) Prepare herbicide solutions in volumetric flasks. Stopper tightly (or seal with paraffin). b) Expose flasks to sunlight for different number of days: 0, 10, 20 and 40 days. Place flasks in refrigerator (5O c or below) after period of exposure. Test the phytotoxicity by bioassay technique after 40 days exposure is completed. c) Prepare petri dishes lined with filter paper. Put seeds of susceptible crop: rice, wheat or oats (100 seeds/ Petri dish). d) Prepare the following herbicide dilutions: 0, 50, 100, 250 and 500 ppm. Apply 10 or 20 ml to Petri dishes. Two or three replicates per treatment.
105
e) Observe growth of seedlings. Make evaluations in 7 or 10 days. Measure growth of shoots and roots. Compare growth of test plants and note the relationship of this with the length of herbicide exposure to daylight. Note:
Chemistry work. Another way to determine if the sunlight
exposure had caused decomposition is to run the samples through T L C or spectrophotometric analysis. A change in peak of wavelength or presence of peaks (metabolites) other than that of the parent molecule will confirm that decomposition had occurred. f) Layout: Treatments and number of Petri dishes needed for each herbicide . ------------------------------------------------------------------------------------------- Herbicide
No. of Petri dishes per exposure ( day )
conc.ppm ______________________________________________________ 0 Water (0)
10
1
2
3
4
9
10
11
17
18
50
20 5
6 12
40
7
8
13
14
15
16 100
19
20
21
22
23
24 250 500
25 33
26
27 34
28 35
40
106
29 36
30 37
31 38
32 39
g) Data: Length (cm) of roots and shoots -------------------------------------------------------------------------------------------Time
Shoot
Root
exposed Conc. ----------------------------------------
-------------------
-----(day)
ppm
I
Mean
II
10
20
I
II
-----------------------------------------------------------------
--------------------------0
Mean
50
:
100
:
250
:
500
:
50
:
100
:
250
:
500
:
50
:
100
:
250
:
500
:
107
40
50
:
100
:
250
:
500
:
Water(0)
:
h) Conclusion : Analyse data and make your conclusions.
2.
VOLATISATION OF HERBICIDES DETERMINED BY LEAF ABSORPTION
Background Vapour
pressure
determines
the
rate
of
volatilization
(vapourisation ) as the temperature rises. When herbicides are sprayed on leaves or on soil surface, part of the chemical may be lost through volatilization. Most of the dinitroanilines (trifluralin, fluchloralin) carbamates (CIPC, EPTC), and phenoxy herbicides (2,4-D esters ) are volatile. For this reason the soil applied compounds (such as the dinitroanilines and carbamates) are incorporated into the soil soon after application to minimize volatilization and hence, the increase in activity. The short chained esters (1to3 of 2,4-D ) are volatile, and the vapours can cause injury to susceptible crops such as cotton, papaya, tomatoes, beans and bananas.
108
Material and Methods a) Prepare herbicide solutions: Herbicides :
2,4-D ( different formulations—Na salt, dimethyl-
amine (DMA ),
isoproylester ( IPE ), and isooctylester ( IOE ).
Concentration: 1000 ppm (this is equal to the concentration of 1 kg a.i./ha in 100 liters of solution). b) Test plants: tomatoes or cowpea grown in small pots, at least 3 plants/pot. Select uniform plants (4-5 leaf stage). Note: Plants should be seeded long in advance before demonstration is conducted. c) Place 100ml of the solution in Petri dishes. Place Petri dish containing herbicide solution besides each potted plants. d) Place test materials under sunlight but not in windy area. Pots should be 2 meters or more from each other. e) Allow 2-5 days and then observe the effect on the plants. Note degree of symptoms caused by each of the herbicides for mutations. Measure growth (weight) after 10 days. f) Data : Number of leaves showing 2,4-D symptoms, degree of injury and weight of shoots.
109
2,4-D
No. of
Degree of Weight
Other
formulat leaves
injury
of
obser-
ion
(%)
shoots
vations and
(g)
remarks
showing symptoms
Na salt
DMA
IPE
IOE
Control
110
3. TO STUDY THE EFFECT OF INCORPORATION OF HERBICIDES IN THE SOIL
Material and Methods a) Herbicide treatments: Trifluralin or EPTC Fluchloralin 1.0 kg/ha. b) Plant groudnut 3 cm deep in pots or seed-boxes.
c) Treatments. Set 1. Apply herbicides, incorporate 3 cm deep and leave under sunlight Set 2. Apply herbicide but do not incorporate; leave under sunlight. Set 3. Apply herbicide, do not incorporate; apply simulation rains 5 cm Set 4. No herbicides (control). d) Observe and record growth of plants (and weeds). e) Data : Germination, height of plant and weight of shoot.
111
Treatment Rep.
4.
Set 1
1 2 3 Total Mean
Set 2
1 2 3 Total Mean
Set 3
1 2 3 Total Mean
Set 4 Control
1 2 3 Total Mean
SIMULATED
Germination Height (%) (cm)
RAINFALL
ON
Weight Others (g)
FOILAR
APPLIED
HERBICIDES
Background Rainfall has two main effects on herbicides: Wash off foliar-applied herbicides and leach down those applied on soils. If rain occurs soon after post emergence application, herbicide activity (retention and absorption) may be reduced. On the other hand, rain soon after application of volatile compounds may reduce volatilization and enhances activity.
112
If rain is too heavy, however, leaching can be very deep that the herbicide will be below the root zone of weeds and will not give the desired control. Alternatively, if the herbicide is brought down to the root zone of the crop, then the crop may be affected severely. In any case, it is important to know to what extent rainfall may influence the activity of a foliar or soil applied herbicide so that necessary precautions could be made to ensure full herbicide activity in field applications.
Material and Methods a) Plant cowpea and barnyard grass in pots b) Herbicides: 2,4-D 1kg/ha; propanil 3kg/ha (one or both) c) When test plants are 14 days old, spray herbicides d) Apply with a sprayer simulated rainfall (1 litre of water/sq m area) as follows: in 10 min. 1, 2, 4, 6 hours after herbicide application. Leave one set without simulated rainfall. e) Replicate 2 or 3. f) Observe and record phytotoxicity of herbicide and measure weight of shoot after 5 days. g) Data : Phyotoxicity rating and weight of shoot
113
Herbicide fb
I
II III
Mean I
II III Mean
simulated rainfall at : 10 min 30 min 1 hour 2 hour 4 hour No rains Control—no Herbicide
5. INFLUENCE OF SOIL TYPES ON HERBICIDE ACTIVITY
Background The factor in the soil that affects herbicide bio-activity are: microorganism, organic matter content, texture and clay contents, pH, exchangeable actions and moisture. Each of these factors affect one way or the other, the biological and chemical degradations, adsorption and leaching, resulting in reduced bioactivity of the herbicide. In most instances, the amount of organic matter is the one single most important factor in reducing bioactivity of soil applied herbicides, due to its ability to adsorb tightly herbicide molecules, depriving their uptake by plants.
114
Material and Methods---A a) Collect 3 or 4 soil types with different contents of organic matter. ( Alternatively, get one soil types and add different proportions of F.Y.M. to achieve different amounts of organic matter in the mixture.) Place them in seed boxes or pots. b) Plant rice/cowpea/wheat, whichever is available. c) Spray atrazine 2kg/ha or 2,4-D 1kg/ha. d) Observe herbicide effects. Is there any difference in plant growth under different soil types? Make your conclusions. e) Data : Phytotoxicity rating and weight of shoots. Herbicide Soiltype
Atrazine
A
2kg/ha
B
Phytoxi
Weight of shoot
city
I
II
III
Mean
C 2,4-D
A
1kg/ha
B C
Control
A B C
Material and Methods----B a) Use of the same soil types as in (A) above. Weight 10 g sample (oven dry basis) and place in test tubes or flasks.
115
b) Add 10ml of 10 ppm herbicide solution: atrazine, 2,4-D, paraquat. c) Shake for 2 hours; filter solution. d) Use filtrate (solution) to germinate susceptible seeds in Petri dish . use rice as test plant. e) Alternatively: Use 1 kg of soil and 1 litre of 10 ppm herbicide solution. Put in buckets and stir for 4 hours. Allow to settle and/or filter. Use 500 ml to spray on field crops. f) Observe the differential effects of herbicides which had undergone adsorption by the soil types. g) Data : Phytotoxicity rating and weight of shoots Herbicide
Atrazine
Soil
Phytoto-
Weight of shoot
Type
Xicity
I
A B C
2,4-D
A B C
Paraquat
A B C
Control
A B C
116
II
III Total
Mean
6
INFLUENCE
OF
FORMULATION
ON
HERBICIDE
ACTIVITY
Background Herbicide are formulated for three main reasons: 1) Make their application easier, 2) Improve their effectiveness under field conditions, and 3) Improve their storage and keeping (safe life) quality. When a herbicide is formulated, the following properties are affected: solubility, volatility, specific gravity, toxicity to plants (due to differential retention and absorption), and many other characteristics. Formulation may involve the following: a) Add other substances, such as surfactants, which can considerably alter the effectiveness of a herbicide. b) Dissolve the active ingredient in a suitable solvent for a liquid formulation. c) Mix active ingredient with inert material such as clay for a wettable powder formulation. d) Add it to a coarse particle such as vermiculite for a granular formulation. e) Combine the ingredients, make a slurry and with pressure produce pellets. Herbicides are formulated to be applied as : a) Solutions of water or oil. b) Emulsions.
117
c) Wettable powder suspensions. d) Granules. Material and Methods a) Test plant : Cowpea planted in seed boxes or pots. b) Spray pre- and post- different formulations of 2,4-D (0.5kg/ha) : Na salt, dimethylamine, IPE, IOE. c) Note germination and phytotoxicity symptoms: measure weight of shoots. Do you see any difference in the plant response to 2,4-D due to the type of formulations? d) Data : Germination, phytotoxicity, and weight of shoots. 2,4-D Formu-
Germi- Phytot-
Weight of shoots
lation
nation
I II III Mean
Na
oxicity
Pre Post
DMA
Pre Post
IPE
Pre Post
IOE
Pre Post
Control
118
7. HERBICIDES IN MULTYCROP SCREENING TEST: DIFFERENTIAL SELECTIVITY Objectives To study herbicide selectivity on several crops as influenced by various factors such as : a) Herbicide formulation (i.e. 2,4-D salt and esters). b) Herbicide types (phenoxy, triazine, ureas, etc). c) Time of application (pre plant, pre emergence, post emergence). d) Method of application (soil incorporation and surface application of volatile compounds). e) Soil interaction (i.e. paraquat applied pre and post).
Methods 1) Plant several selected crops and weeds thickly in rows ( at least 2 rows per crop). Suggested crops are: rice, wheat, oats, maize, sorghum, pearlmillet, fingermillet (ragi), cotton, safflower, sunflower, groundnut, chickpea, pigeonpea, mung, cowpea, okra (bhindi), eggplant (brinzal), tomato, cluster beans, raddish, cabbage, spinach, onion, pepper, gourd, cucumber, melon. Weeds : Echinochloa, Digitaria, Amaranthus, Portulaca, Celosia etc. 2) Spray herbicides across the rows (at least 1.5 m wide). CAUTION : Calibrate sprayer before applying any herbicide solution. 3) Evaluation. Measure herbicide effects in terms of:
119
a) Number of plants in row-plot and weeds per sq m and b) Subjective visual rating where 0= no control and 100= complete control. Also, take not of: b- 1) Distinctive phytoxicity symptoms of different herbicides, and the b-2) Crops/weeds that are tolerant (safe, resistant) and susceptible. 4) Write and submit observations and data. Give conclusions. HERBICIDES IN MULTICROP SCREENING TEST Pre- and Post-treatments Plot size: -----------------------
Treatments applied: -----------
Planted: -------------------------
Pre emergence: ----------------
Post emergence: ---------------------No. Herbicide
Rate
Formulat Amount Plot
Kg/ha*
ion (EC, WP, WS. %)
1
2,4-D Na
1.0 Pre
80WS
2
2,4-D Na
1.0 Post
80WS
3
2,4-D amine 1.0 Pre
720EC
4
2,4-D amine 1.0 Post
720EC
5
2,4-D EE
1.0 Pre
360EC
6
2,4-D EE
1.0 Post
360EC
7
Diuron
1.0 Pre
80WP
8
Atrazine
1.5 Pre
50WP
120
per plot
number
9
Simazine
1.5 Pre
50WP
10
Terbutryn
1.0 Pre
80WP
11
Nitrofen
2.0 Pre
250EC
12
Alachlor
2.0 Pre
500EC
13
Butachlor
2.0 Pre
500EC
14
Fluchloralin 2.0 Pre
480EC
Inc 15
Fluchloralin 2.0 Pre
480EC
16
Dichloramat 2.0 Pre
450EC
e 17
Paraquat
0.5 Pre
18
Paraquat
1.5 Post
19
Control
------
200EC 200EC --------
Based on acid equivalent (a.e.) for 2,4-D and active ingredient (a.i.) for other compounds. Calculate the amount of chemical per plot before going to the field. Weight the amount of WP chemicals in the laboratory. Wash (clean) sprayer before putting the next chemical during herbicide application. Irrigate the plots with sprinkle system to minimize movement of herbicides from one plot to another. Form A: List the crops and weeds with regard to their tolerance and susceptibility to the treatments.
121
Treatment
Crop /weed response
Number Tolerant
Slightly
Susceptible
Tolerant
Very Susceptible
Date of data taken: ---------------------------Form B: Evaluation—visual rating of crop-weed response to herbicide treatments. Plot
Crop /weed species
No.
------------------------SR GR SR GR SR GR SR GR SR
122
GR SR GR SR GR SR GR SR SR GR SR GR SR---% stand reduction or control; GR---%growth reduction of plants surviving Date evaluated: --------------------- Evaluated by: ------------------Remarks :
123
Form C : Herbicide symptoms on crops Herbicide
Description of symptoms / effects on crops
Date observed: ------------------------------ Taken by -----------------------------
8. EQUIPMENT AND APPLICATION TECHNIQUES FOR CHEMICAL WEED CONTROL A. EQUIPMENT
C. PRECAUTIONS
a) Types of sprayers
a) Steps
b) Important accessories
b) Precautions
B. CALCULATION
D. PREPER APPLICATION
Objectives 1) Know the various types of equipment that can be used for herbicide application :
124
a) equipment for ground, tractor and aerial applications( advantages and disadvantages), b) assembly and modification of spray booms and other spray equipment, c)
characteristics of nozzles for broadcast, band, directed, spot and other application methods, and
d) learn various precautions in the use of herbicide sprayers and equipments. 2) Understand the calculation of herbicide applications, volume of solution per area covered by spray boom with different nozzle distances, etc. 3) Learn how to calibrate sprayers. 4) Beable to apply herbicides (sprayable and granules) accurately and uniformely in the field. 5) Understand the importance of accurate herbicide application. 6) Learn the proper maintenance procedures of herbicide sprayers and equipment. THINGS TO KNOW AND DO BEFORE GOING OUT TO SPRAY IN THE FIELD Materials 1) Sprayers and equipments: a) Sprayers with 1, 2or more nozzles, b) Knapsack sprayers of different capacities, c) Other types of sprayers and d) Granular applicators (manually operated).
125
2) Spray boom with different nozzle capacities (25 and 50 cm spacing’s) 3) Assortment of nozzle types: flat fan, even flat, flood fan, full cone, hallow cone, etc. 4) Flat fan nozzles 650 and 800 angle spray. 5) Assortment of damaged and worn out flat fan nozzles. 6) Pressure gauge and pressure gauge regulators. 7) Several nozzle blanks to shutoff nozzle tips on booms. 8) Measuring cups, graduated cylinders, test tubes, bucket or pail, metre tap, metre stick. 9) Water, red food colouring. 10) Several different spray equipment company catalogues.
Procedure, Demonstration and Discussion 1) Examine the different types of sprayers. Try to operate some of them and note
which type would be easiest and most
suitable to use for herbicide application a) Manually operated -------------------------------------------b) Power-driven--------------------------------------------------2) From the above sprayers, select one for the following demonstration work. Select one also for the application of granular herbicides. 3) Gather data for the following situations. Record your observations on the space provided.
126
a) Nozzle types: Fill spray tank with water and add a drop of food colouring. Set pressure at 30 psi. Gather data on the items below. Nozzle types Flat –fan :
Even –flat:
Flood –fan : Full cone : Hallow cone
A. Draw the spray pattern 1) Side view
2)
Top view
B. Volume of water delivered (collected), ml/10 sec.
-------------------------------------------------------------------------------------------
(
)
(
)
(
)
(
)
c) Nozzle flow rate : Compare the amount of water collected for 15 seconds from an 8002 and 8004 flat fan nozzle at 40 psi.
127
Nozzles size
Company reading
Amount collected
Remarks 8002
---------
8004
a)
--------------
---------------
------------------
Nozzle angle : Compare the spray pattern (point overlap and
volume collected at given heights) of 8002 and 6502 nozzles. Places two nozzles (spaced 50 cm) in a boom. Set psi at 40 pounds. Observe spray pattern and spray overlap at heights of 20, 30 and 40 cm.
Nozzle
8002
Height
Overlap
(cm)
(yes, no)
Volume collected (ml)
20 30 40
6502
20 30 40
b)
Height of boom : This item has been demonstrated above. Let us
have more data. Nozzles 8002, spaced 25 cm, 3 in a boom. Set pressure at 40 psi, height of spray boom at 10, 20, 30 and 40 cm. record pattern of spray, pattern of water level collected and indicate the point where single covereage and double overlape occurred.
128
Pattern of spray and point Pattern of water level where single coverage and collected ( ml ) for 15 double overlap occurred
c)
seconds
10 cm
10 cm
20 cm
20 cm
30 cm
30 cm
40 cm
40 cm
Nozzle spacing on boom : Use 3 flat fan 8002 nozzles at 40 psi
with about 30 cm height of boom. Compare 25 and 50 cm nozzle spacings. Draw the spray pattern, observe overlap: and the level of water collected for each spacing. What effect dose nozzle spacing have on amount of discharge and spray pattern at a given height? Height of spray pattern and point of overlap boom (cm) 20
50
Remarks :
129
Level of water collected (ml)
d)
Spray pressure: Set nozzle (8002) at 50 cm apart and boom at
20 cm height. Operate at 10, 20 and 40 psi. Observe spray overlape, size of spray droplets at each pressure setting and collect the volume of water delivered in 15 seconds at each pressure setting. How dose the pressure setting affect the amount of discharge and droplet size ? How do your readings for water data collected and compare with the company catalogue information ? Psi
Vol. water
Spray
Spray
collected
droplets pattern
Overlap
10
20
40
Remarks :
g) Damaged and worn out nozzles : Use 25 cm spacing, 3 nozzles, 30 psi and adjust height for single coverage. Place one worn out 8002, one 8002 cleaned with a piece of wire (damaged) and one new 8002 nozzle on boom outlets. Place new nozzle on centre outlet of boom. Compare
130
the spray pattern of these nozzles and indicate by drawing each. How dose this affect spray pattern uniformity? Collect discharge from each nozzle for 15 seconds. What effect dose worn out, damaged or new nozzles have on the amount of herbicide applied? Nozzle
Vol. of water
Company
Spray pattern
in 15 sec
catalogue data (draw) and degree uniformity
Damaged
Worn out
New
Remarks:
131
of
Evaluation of spraying patterns of different types of spray pumps and spray lances. Type of sprayer/spray lance
Width of Time
Volume of
boom (cm required water or m)
for
required
spraying for one acre acre (hours) A Knap-sack sprayer fitted with flat fan nozzle B
Knap-sack sprayer fitted with flood zet nozzle
132
(litres)
one
C Knap-sack sprayer fitted with cone type nozzle D Knap-sack sprayer fitted with double nozzle spray lance E Knap-sack sprayer fitted with multi nozzle spray lance F Back pack power sprayer G Tractor operated sprayer H Anyother
available
equipment
133
canarygrass_reed
campion_white
campion.bladder.plant
campion.bladder.flower
134
cactus
buttercup_smallflower
buttercup_matureb
buttercup_mature
135
buttercup_common
buttercup.spp.plants.
buttercup.spp.plant.
burdock_plant
136
burdock.woolly.plant
burdock.woolly.bur.j
burdock
bunchberry.plants.
137
bunchberry.plant
bulrush.black.plant
buckwheat_wild_seedling
buckwheat_wild_plant
138
buckwheat_common
buckwheat.wild.plant
buckwheat.wild.flowe
bryony_white
139
browneyed_susan_flower
broomrape_crenate_flowerplant
broomrape.singleflower.plant
broomrape.singleflower.flowers
140
bromegrass_smooth_seedhead
bromegrass_smooth
brome_rattlesnake
brome_downy_seedhead
141
brome_downy_mature
brackenfern
bouncingbet_plants
bouncingbet_plant
142
boneset.plant
boneset.flower
bluets.plant.
bluets.flower.
143
CHAPTER 5
CLASSIFICATION OF HERBICIDES SELECTIVITY A non-selective herbicide kills or damages all plant life in a treated area (e.g., Roundup). A selective herbicide will kill weeds in a germinating or growing crop without harming the crop beyond the point of recovery (e.g., 2,4-D used to control broadleaved weeds in a grass pasture; Avadex to control wild oats in cereals.) Factors Which Influence Selective Action of Herbicides
Table 5. Weed Susceptibility to 2,4-D Susceptible Plant form
Tolerant or Resistant
erect
spreading, prostrate
Leaf shape
broad, large
narrow, short or linear, eg., grasses
Leaf position
horizontal, rosettes formed
upright or pendulous, rosettes lacking
Leaf surface
rough, hairy
waxy, very hairy, corrugated
Growing point terminal, axillary
protected (sheath, crown)
Root depth
shallow
deep
Condition
growing actively
dormant
Age
young
mature
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Nature of the Weed Perhaps the most important consideration in selectivity is the nature of the weed itself. A listing of characteristics associated with 2,4-D susceptibility and resistance will serve as an example: The first five characteristics in the previous list are associated with the amount of spray which will make initial contact with the plant and the plant's subsequent ability to retain toxic materials on leaf and stem surfaces. Studies with a large number of plant species have indicated that, in general, those having the characteristics on the left are injured more by a herbicidal application than are those having the characteristics listed on the right. Biochemical Selectivity Some plants can tolerate a given amount of herbicide within their tissues, whereas others will succumb due to the differing chemical makeup of the plants concerned. It is thought that the resistant plant is able to break down the herbicide to nontoxic components, whereas the susceptible plant cannot. Comparing corn, which is resistant to atrazine, with oats, which is susceptible, the greater amounts of atrazine which accumulate in the oat leaves and eventually kills the plant are due to three factors: oats absorb more atrazine, translocate it more effectively, and cannot break it down as readily. It is important to note that biochemical selectivity can be lost if excessive herbicide rates are applied. Depth of Rooting: Most germinating weeds arise from seeds in the top one-quarter to one-half inch of soil. A soil applied herbicide
145
will be taken up by weed roots in this zone, whereas crop seeds planted deeper than this will germinate in a herbicide free zone. Influence of Herbicide on Selectivity: The herbicide itself can influence selective action due to: a. Nature of the chemical molecule; b. the concentration applied; c. the formulation used; d. surface tension and spreading qualities. Selective action is observed for example where MCPB (a 4 carbon chemical) is used for weed control in clover or peas. The weeds are able to change the MCPB to MCPA (a 2 carbon chemical) which is much more toxic than the original herbicide. The crop cannot do this, so in essence the weeds commit suicide. Exceeding recommended use rates can kill or injure normally tolerant non-target plants. Use of oil soluble ester formulations of 2,4-D are often more effective on many weeds than water soluble amine formulations as they can more easily penetrate the waxy coating on plant leaves. MODE OF ACTION(or how the herbicide works to kill a weed) Contact herbicides - kills plant parts covered by the herbicide and are directly toxic to living cells. There is little or no translocation or movement of the material through the plant. Contact herbicides are effective against annual weeds but they only "burn off" the tops of perennial weeds - chemically mowing them. Contact herbicides may be selective, such as Torch (bromoxynil) which kills broadleaved weeds in cereals without damaging the crop, or nonselective, such as Gramoxone (paraquat) which kills any green plant material.
146
Systemic herbicides - absorbed by either the roots or above ground parts of plants, these herbicides move or are translocated in the plant. They exhibit a chronic effect; that is, the full effects may not show for a week or more after treatment. An overdose on the leaves may kill the leaf cells more quickly, thus preventing translocation to the site of action in a plant. The old axiom "If a little is good, more will be better" does not apply to herbicide use rates. Systemic herbicides can be selective, as in the case of 2,4-D, MCPA, Banvel and Tordon or non-selective, as with Roundup. Soil Sterilants - chemicals which prevent growth of plant life when present in the soil. These products will prevent plant growth for periods of a few months to a number of years. Examples include bromacil, tebuthiuron and atrazine at high rates. TIMING OF APPLICATION Pre-Plant Soil Incorporated - these herbicides are applied to the soil before the crop is sown. They are incorporated in the soil to prevent loss due to vapourization and breakdown by sunlight. Trifluralin and EPTC are examples. Pre-Emergence - applied to soil prior to seeding or after the crop is sown but before crop and weeds emerge. In most cases, the weeds germinate in treated soil while the crop germinates below the herbicide zone. Post-Emergence - sprayed directly on the weeds after they are up and growing.
147
Table 6. Comparison of Soil-Applied and FoliarApplied Herbicides Source: Weeds '81 Alberta Agriculture HERBICIDE TYPE: PRE-PLANT INCORPORATED ( Soil Applied) Advantages: 1. Early control of weeds, minimizing competition. 2. Weeds are controlled where wet or windy weather after emergence can delay spraying. 3. Work load is distributed. Disadvantages: 1. Perennial weeds are generally not controlled. 2. Less effective under dry or cold soil conditions. 3. Residue may restrict crop rotation the following year. 4. Soil erosion may be a problem, as additional tillage for incorporation is required. HERBICIDE TYPE: PRE-EMERGENCE INCORPORATED (Soil Applied) Advantages: 1. Early control of weeds, minimizing competition. 2. Weeds are controlled where wet or windy weather after emergence can delay spraying. 3. Planting and herbicide application may be done in
148
one operation. Disadvantages: 1. Less effective under dry or cold soil conditions. 2. Perennial weeds are generally not controlled. 3. 0n sandy soils, heavy rains may leach the herbicide down to the germinating crop and cause injury. 4. Wet or windy conditions after seeding can delay application until crop emergence and prevent herbicide application. 5. Planting may be slowed down by combining planting and herbicide application. 6. Residue may restrict crop competition the following year. 7. Soil erosion may be a problem, as additional tillage for incorporation is required. HERBICIDE TYPE: POST-EMERGENCE (Foliar applied) Advantages: 1. Type and density of weed can be seen before herbicide application. 2. Oil texture does not directly affect herbicide choice or performance. 3. Oil moisture has little influence on level of control. 4. Few post emergent herbicides leave a soil residue which will restrict subsequent cropping rotation. 5. Incorporation tillage is not required. 6. Top growth control of several perennial weeds is possible.
149
Disadvantages: 1. Specific stage of application required on both crop and weed variable emergence may be a problem. 2. Flush of weeds after spraying generally not controlled. 3. Wet or windy weather can delay application.
PERSISTENCE OF HERBICIDES IN THE SOIL The length of time that a herbicide remains active or persists in the soil is extremely important as it relates to the length of time that weed control can be expected. Also, residual activity is important as it relates to phytotoxic after-effects that may prove injurious to succeeding crops or plantings.
Seven factors affect the persistence of a herbicide in the soil; 1. 2. 3. 4. 5. 6. 7.
micro-organism decomposition, chemical decomposition, adsorption on the soil colloids, leaching, volatility, photodecomposition, and plant uptake.
Micro-Organism Decomposition
150
The principal micro-organisms in the soil are algae, fungi, actinomyces, and bacteria. They must have food for energy and growth. Organic compounds of the soil provide this food supply, except for a very small group of organisms that feed on inorganic sources. Microorganisms use all types of organic matter, including organic herbicides. Some chemicals are easily decomposed (easily utilized by the microorganisms), whereas others resist decomposition. Chemical Decomposition Chemical decomposition destroys herbicides through interaction with the soil constituents of oxygen, hydrogen or water. Hydrolysis (interaction with water), for example, is responsible for inactivating atrazine in the soil. Adsorption of Herbicide by the Soil Herbicides tend to leave the soil solution and are adsorbed by clay and organic matter particles making the herbicide unavailable for uptake by the weed.
Research has shown that: • Soils
high in organic matter require relatively large amounts of pre-emergence and soil sterilant herbicides for weed control. • Soils high in clay content require more herbicide than sandy soils for pre-emergence or soil sterilant weed control. • Soils high in organic matter and clay content tend to hold the herbicides for a longer time than sands. The adsorbed herbicide may be released so slowly that the chemical is not effective as a herbicide.
151
Leaching Leaching is the movement of a herbicide in solution through the soil. Leaching occurs in any direction (downward, upward, sideways). The extent to which a herbicide is leached is determined principally by: • Solubility
of the herbicide in water. of water passing through the soil. • Adsorptive relationships between the herbicide and the soil. • Amount
In general, those herbicides which are completely water-soluble are most easily leached. Salts of 2,4D are water-soluble and leach readily through porous, sandy soils whereas esters of 2,4-D are low in solubility and do not leach easily. Herbicides have been known to move upward in the soil. If water evaporates from the soil surface, water may move slowly upward. The water may carry with it soluble herbicides. As the water evaporates, the herbicide is deposited on the soil surface. Volatility Herbicides may evaporate and be lost to the atmosphere as volatile gases. The volatile gases may or may not be toxic to plants. The volatile gases may drift to susceptible plants such as those from the ester forms of 2,4-D causing injury to susceptible crops such as tomatoes or grapes. Eptam, Eradicane and Treflan are examples of volatile herbicides which must be incorporated into the soil immediately following application to prevent loss of herbicide to the atmosphere.
152
Rain or irrigation water applied to a dry soil will usually leach the herbicide into the soil, or aid in its adsorption by the soil particles. Once adsorbed by the soil, the loss by volatility is usually reduced. Photodecomposition Ultraviolet light from the sun decomposes many herbicides applied to the soil surface. Some herbicides such as Treflan are recommended for soil incorporation as they break down readily when exposed to sunlight. Plant Uptake The uptake of herbicides by plant roots results in their removal from the environment; hence, reduced concentrations in the soil. 1) Based on Chemical Nature. Compounds having chemical affinities are grouped together. This si useful in listing and characterizing herbicides but tells little or nothing concerning the methods by which they are employed. 1) Inorganic herbicides:
Contain no carbon atoms in their
molecules. They were the first chemicals used for weed control before the introduction of the organic compounds, examples are: Acids:
Arsenic acid, arsenious acid, arsenic trioxide, sulphuric
acid. Salts:
Borax, copper sulphate, ammonium sulphamate, Na
chlorate, Na arsenite 2) Organic herbicides: Oils and non oils- containing carbon and hydrogen in their molecules.
153
--- Oils: Diesel oil, Stoddard solvent, xylene- type aromatic oils, polycylic aromatic oils etc. --- Aliphatics: Dalapon, TCA, Acrolein, Glyphosate, Methyl bromide ---Amides ( and acetanilides) : Propanil, Butachlor, Alachlor, CDAA, Daphenamid Niptalam, Propachlor -- Benzoics: 2,3,6-TBA, Dicamba, Tricamba, Chloramben, fenae -- Bipyridyliums : Paraquat, Diquat -- Carbamates : Propham, Chlorpham, Barban, Dichlormate, Swep, Terbatol -- Thiocarbamates: Butylate, Dillate, Trialate EPTC, Molinate, Pebulate, Vernolate, Benthicarb, Aslum, Cycolate -- Dithiocabamates: CDEC,Methan -- Nitriles (benzonitriles): Dichlobenil, Bromoxynil, Ioxynil --Dinitroanalines(to luidines) : Benefin, Nitralin, Trifluralin, Butralin, Dinitramine, Fluchloralin, Oryzalin, Penoxalin --Phenols: Dinoseb(DNBP), DNOC (sinox), PCP --Phenoxy: 2,4-D, 2,4,5-T, MCPA, MCPB, 2,4-DB, 2,4-DP, 2,4,5-TP (sivex). --Triazines:
Atrazine,
Simazine,
Ametryne,Terbutryne,
Cyanazine, Cyprazine, Metribuzin, Prometryn, Propazine --Ureas:
Monuron, Diuron, Fenuron, Neburon, Fluometuron,
Methabenzathiazuron,
Buturon,
Siduron, Metoxuron -- Uracils: Bromacil, Terbacil, Lenacil
154
Chloroxuron,
Norea,
-- Diphenyl ethers: Nitrofen, Fluorodifen --Organic arsenicals: Cacodylic acid, MSMA, DSMA --Others: Bentazon, Picloram, Pyrazon, Pyrichlor, Endothall, Bensulphide, MH, DCPA 2) Based on Mode of Action (Physiological) or According to Use 1) Selective—contact and translocated—more toxic to some kinds of plants than to others. 2) Non-selective- contact and translocated-toxic to most plants. 3) Foliage- active- contact and translocated- effective when applied through the leaves (post emergence) 4) Soil-active-contact-fumigant and translocated-effective against germinating seeds or absorbed by roots to be effective(pre-emergence) Contact herbicide kills only the plant parts to which the chemical is applied. It is most effective against annual weeds. Translocated (systematic) herbicide is absorbed either by roots or aerial parts of the plant and is then translocated within the plant system to tissues that may be at a distance from the point of application where it exerts its phytotoxic action. It is effective against established perennial weeds, since uniform coverage is not as critical as with contact herbicides. Contact herbicides kill most plants immediately, but systematic herbicides often have a chronic effect, sometimes achieving results in a week or a month after treatment. Selective and nonselective chemicals exist for both the systemic and contact types of herbicides.
155
DETAIL CLASSIFICATION WITH EXAMPLES A. Selective Herbicides. 1) Foliage applied herbicides a) Contact type bromoxynil dinoseb
KOCN
propanil
nitrofen
selective
paraquat
sulphuric
weed oil diquat acid endothall
phenmedipham
b) Translocated type barban
MCPA
2,4-D
dalapon
mecoprop
2,4-DB
dicamba
MSMA
2,4,5-T
dichlorprop
picloram
2,4-DP
DSMA
2) Soil—applied herbicides alachlor
dinoseb
propachlor
atrazine
diphenamid
propham
benefin
diuron
pyrazon
bensulide
endothall
seson
bromacil
fluometuron
siduron
CDAA
linuron
simazine
CDEC
molinate
TCA
chloramben
monuron
terbacil
156
chloroxuron
naptalam
terbutryn
cyanazine
nitralin
triallate
cycloate
nitrofen
trifluralin
cyprazine
norea
vernolate
DCPA
pebulate
dichlobenil
prometryne
B. Non-selective Herbicides 1) Foliage applied a) Contact herbicides ASM
dinoseb
cacodylic acid
paraquat
diquat
PCP weed
oil b) Translocated herbicides amitrole
DSMA
silvex
dalapon
erbon
2,4-D
dicamba
MSMA
2,4,5-T
picloram 2)
Soil applied herbicides
a) Soil fumigants carbon bisulfied
methyl bromide
methan
methyl bromide chloropicrin
b) Residual soil herbicides atrazine
erbon
borates
fenac
157
picloram prometon
bromicil
karbutilate
simazine
chlorates
linuron
2,3,6-TBA
dicamba
monuron
TCA
diuron C. Aquatic applications acrolein
endothall
copper sulphate
fenac
dichlobenil
2,4-D
diquat
grade(b) xylene
3) Based on Time of Application in relation to Crop and Weed Growth 1) Pre –plant (pre-sowing) herbicide-applied before a crop is planted to control existing weeds as in minimum tillage situation or to kill germinating weeds if the field has been prepared and ready to be planted. The herbicide is usually incorporated into the soil to reduce volatility and photo decomposition. Paraquat, Basalin. 2) Pre-emergence herbicides—is one which is most effective when applied before the emergence of crop and weeds or this term may also refer to herbicide use after crop has emerged but before weeds emerge. 3) Post-emergence herbicide—is one which is mosteffective when applied after the emergence of crop and weeds or this term may also refer to herbicide use after crophas emerged but before weeds emerge. The choice of the time of application will depend on the selective action of the herbicides, tolerance of crop to herbicides and type of
158
weeds to be controlled. Herbicides that inhibit germination or are absorbed through the roots are applied pre-emergence whereas those which are absorbed and translocated through the leaves are applied post-emergence. In general, however, the stage of the crops and weeds are
the same under pre-emergence situation or post-emergence
situation, that is, both weeds and crops have not emerged when preemergence herbicide is applied and both weeds and crop have emerged when post-emergence herbicide applied. Thus application of herbicides when either crop or weeds have emerged (modified situation) requires a specific statement to describe the growth stages of bith weeds and crops. HERBICIDES AND THEIR METHODS OF APPLICATION a) Broadcast (blanket-overall)—uniform application to an entire, specific area, including over crop plants. b) Band—application to a strip over or along crop row. (This method reduces costs since treatment is confined to a portion of the total area). c) Directed—herbicide is applied to particular weeds or to soil in such a manner as to insure minimal contact with desirable plants (thus, it is possible to use non-selective herbicides in a selective manner). d)
Spot—application to a limited area such as small patches or
clumps of a serious perennial weed or weeds which were not controlled by previous cultivation or herbicide applications. e) Basal application —application to stem or trunks at or just above the ground line by sprayer or paint brush.
159
f)
Soil application—application to the soil rather than to
vegetation. g)
Soil incorporation—use of tillage implements to mix the
herbicides with the soil. h)
Soil injection (sub- surface)—application beneath the soil
surface, of soil active herbicide, by means of special equipment to provide a layer of herbicide—treated soil at a specified depth. i)
Foliar application—application on the foliage of plants.
FORMULATIONS Pesticides in general and herbicides in particular, in their natural state, may be solid, liquid, volatile, non-volatile, soluble or insoluble. Ingenuity is required to prepare suitable mixtures of these materials for use on the farm, in the forest, in the home, or in the industrial and public health pest control programme. a) Why formulated ? To have a product with physical properties suitable for use in different types of application equipments and under a variety of conditions. To prepare a product which is biologically effective and economically feasible to use. To prepare a product which is suitable for storage purposes under local conditions. Farmers should, therefore, be as familiar to formulations as with the toxicant. Undiluted herbicide is seldom used and the formulated chemical may behave differently in mixtures than in the pure state.
160
Classification of herbicides according to type of formulations 1) Emulsifiable concentrates ( EC) 2) Wettable powders
(WP)
3) Granules
(G)
4) Water soluble concentrates (WSC) OR aqueous (WSA) 5) flowable concentrates
(FC) etc.
Detailed classification according to type of formulation A. LIQUIDS 1. Water soluble chemicals—solution concentrate
2. Non-water soluble chemicals-emulsifiable formulations
161
B. Dry solids 1.
Water-soluble
chemicals—soluble
powder
or
granular
formulations
2.
Non-water soluble chemicals—wettable powder, granular or
liquid suspension formulations Wettable powder
162
Granular
Liquid Suspension
163
FACTORS AFFECTING HERBICIDE EFFECTIVENESS The Weed Leaf For foliar active herbicides, the chemical must be retained on and penetrate through the leaf surface. Wax cuticle, hairs on the leaf and the angle of the leaf all determine retention and adsorption. Surfactants or surface active ingredients can be added to herbicide formulations to increase their wetting ability and penetration into the leaf. Climate Under dry or cool conditions, plants grow slowly and translocation of systemic herbicides is slow. Cloudy conditions interfere with food production in the plant thereby slowing translocation and reducing effect of systemic herbicides. High temperatures and low humidity increase evaporation of the herbicide from the weed leaf. The weed leaf surface is also difficult to penetrate under these conditions as the plants tend to develop a heavy wax cuticle. High humidity often damages the leaf cuticle allowing for a high absorption of herbicide into the weed. Warm temperatures and high humidity are generally favoured for best control with systemic herbicides. Avoid spraying in wind as herbicide will be lost to drift. Rainfall during or after application can wash the herbicide off the leaf, hence, reducing effectiveness; but rain or irrigation is required for many soil applied herbicides such as Dual and Primextra. Always read the herbicide label to determine under which environmental conditions the product will work best. Time of Day This factor relates both to temperature and light. Generally carbohydrate levels in the leaves are lowest in the morning and highest in the late afternoon. Spraying early in the morning is more effective.
164
Age of Weed As a rule, weeds in the seedling stage are usually most susceptible to herbicides. Young weeds are growing actively and there is a great deal of movement of food and water throughout the plant. Systemic herbicides, once inside the plant, will be moving with this material to the growing points. With established perennial weeds, such as Canada thistle, treatment at the bud or early flower stage is usually more effective. This is because the root food reserves are expended and newly produced food along with herbicide is being moved back down to the root system to again build up reserves. With Canada thistle and other perennials, it is the root we must attack for control. It is critical to follow herbicide label directions regarding stage of weed growth to obtain optimal control. Nutrition Herbicide injury to weeds is greatest when nutrient levels are high and the weeds are growing vigourously. Adequate fertility also improves weed control by increasing competition by the crop. Cultivation Chemical weed control is more effective in fields that are cultivated because more weed seeds are brought to the surface to germinate. With perennial weeds, cultivation lowers the root reserves making them more susceptible to herbicides.
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Soil Organic Matter Soils with high O.M. such as peats or mucks require higher rates of chemical than do sandy soils. This is because more of the chemical is bound to the soil colloids in high O.M. soils. Soil Texture Higher herbicide rates are needed on silts and clays because they provide more surface area for chemical binding. Sandy soils require the lowest rates. Soil Moisture For soil applied herbicides, even mechanically incorporated products, some moisture is required to place them in the soil solution for weed uptake. Soil herbicides generally work best in a warm, moist soil. Chemical Compatibility Some chemicals, when present in combination with other chemicals, are more toxic to plants and animals than when present alone. If the field has been sprayed with a herbicide previously, spraying with another chemical may cause great crop damage. Read the label to determine compatibility with other pesticide products. SOME PROBLEMS ASSOCIATED WITH HERBICIDE USE Injury to the crop. Faulty applications and environmental factors can lead to crop damage from herbicides.
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Residues in the crop. Herbicide residues in crops cannot exceed the safe and acceptable levels set by the Federal government. In many cases you will see recommendations telling you not to apply chemicals within a certain number of days of harvest or excessive chemical levels in the food will result. Residues in soil. Some chemicals persist in the soil in phytotoxic concentrations. The land manager must be aware of this if susceptible crops are to be planted subsequently. Compatibility with other pesticides. Two chemicals mixed together might cause crop injury where either one would not when applied separately. Occupational hazard. Herbicides as a rule are quite safe to use, having a low toxicity to man and animals. All precautions must be taken, however, to protect the applicator and persons who may come in contact with the chemical. Air pollution. a) Spray droplet drift. b) Vapour drift (volatile gases)
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Water Pollution. Herbicides may enter water courses and groundwater either by direct application through accident or indirectly via leaching and runoff from sprayed areas. Disposal of used containers. Irresponsibility in disposal of used pesticide containers sometimes leads to poisonings of animals and man. Resistant weeds Weed populations contain a very small number of individual plants that are naturally able to withstand a particular herbicide (or herbicide group) which is registered to control the weed. This naturally occurring resistance is not due to weather conditions or application technique but is an inherent characteristic of the genetic makeup of the resistant plants. Because of their low frequency of occurrence, these resistant plants go undetected. The continual use of the same herbicide (or herbicide group) year after year allows them to set seed and multiply. Futhermore, by removing the susceptible weeds, there is more opportunity for the resistant strain to flourish. It is important therefore to know the herbicide groups so herbicides with different mechanisms of action can be selected as of the strategy in preventing a build up of resistant weeds. information on herbicide groups refer to the Field Crop Guide Commercial Growers.
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that part For For
Managing Resistance • rotate
crops. This usually results in using a diversity of herbicides. • rotate herbicides with different modes of action. • use tank mixes that control the target weeds by different modes of action. • use short residual herbicides whenever possible. Use long term residual herbicides wisely and not continuously on the same field. • integrate herbicide use with other weed control strategies. • Practice good sanitation practices to prevent movement of weed seed with soil, machinery, crop residue, etc. Effects on wildlife Some animals depend on weeds as a food source. Altering the botanical flora could have detrimental effects on some animals but in turn could lead to a better environment for others. Great care must be exercised when using herbicides in or adjacent to riparian areas. Read labels or contact habitat management personnel for information on setbacks from watercourses and riparian zones. WEED MANAGEMENT PLANNING In any weed management program it is often the little things that can spell success or failure and it is often these same items that effect the cost of weed control. As with other aspects of successful farm management, weed control requires an equally high level of management to obtain optimum control while minimizing costs.
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A successful weed management program requires the producer to undertake three basic steps: Step 1. Diagnosis of the problem Identify the weed Know your enemy! Just as a doctor cannot prescribe a cure for disease until he has identified the causative agent, so can you not choose a cure for your weed problem without first knowing the plant you are dealing with. Failure to properly identify the problem leads to dollars unwisely spent on control options. For example, Basagran is registered on peas and beans for control of hairy nightshade. It will not, however, control its relative, black nightshade. As another example, Treflan provides generally good control of many annual broad-leaved and grassy weeds in peas. It does not however, control any mustard family weeds. If you fail to identify shepherd's purse (a mustard) you won't get control. It is also important to know something about the biology of the weed. Is it a perennial or an annual? If perennial, is it taprooted or creeping-rooted? If annual, is it a winter annual or a summer annual? This knowledge is critical to choosing control strategies and timing. Identify the problem Listen to your weeds. Weeds in crops are more often the result of a problem and not the cause. They often simply fill in environmental voids caused by such factors as: • •
poor seedbed preparation results in uneven crop germination and therefore less competition for weeds. poor land preparation. Don't seed into a weed problem. If land to be used for crop production is infested with tough perennials like quack grass, failure to control prior to seeding invites disaster. You must control it (chemically or mechanically) prior
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• • •
•
•
•
to seeding or rotate to a crop where selective control is available. Black nightshade for example is not easily controlled in peas and beans but is effectively controlled by registered herbicide options in corn. Use of perennial forages for a number of years will also reduce a black nightshade problem. poor drainage. Buttercups and bog rush (slough grass) have a preference for wet soils so are indicative of poor drainage. poor fertility. soil pH. Weeds such as bracken fern grow best in acid conditions while others such as foxtail barley show a preference for higher pH soils. Amending the soil reaction can reduce the competitive advantage enjoyed by such indicators. diseases/insects. Pest organisms attacking beneficial plants weaken their competitive ability and predispose an area to weed invasion. In past years dandelions were thought to be the cause of failure of new seedings of alfalfa. Investigation showed that the disease organism, Verticillium wilt, was attacking the crop and dandelions were just filling in the environmental void left by a non-competitive crop. resistant weeds. Routine cultural practices and repeated use of the same herbicide hastens build-up of weeds resistant to those practices. Over reliance on atrazine for weed control in corn has resulted in a build-up of resistant weed populations (particularly groundsel, redroot pigweed and lamb's-quarters). Some of these weeds are now resistant to 20 times the rates that once controlled them. This creates another problem in that these resistant weeds can limit control options in rotational crops. Metribuzin, used in processing pea production, is in the same chemical family as atrazine. It could not be considered as an effective option when rotating from corn to peas if resistant weeds were present. (See section on Managing Herbicide Resistance, page 28). weed population shifts. Continued use of one management strategy can result in changes in the weed population. Atrazine herbicide, for example, has controlled most broadleaved weeds in corn but by so doing has created more space for grasses such as green foxtail and barnyardgrass which are only partially controlled.
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•
•
•
microbial degradation. Annual use of the same herbicide can result in huge increases of soil microorganisms that use the product as an energy source. Eradicane, continually used in corn production, has in some areas been quickly decomposed by soil microorganisms, resulting in poor weed control. weather effects. Failure to be aware of weather effects on herbicide activity often results in poor weed control and crop damage. Herbicides are less effective in cool, wet conditions. Heavy rains soon after a foliar application wash the herbicide from the leaf before they can enter the plant. Excessive rains can also leach the herbicide into the soil and result in crop damage and poor weed control. Wet conditions make soil preparation difficult and result in poor herbicide distribution over the soil and again poor weed control. lack of Total Farm Weed Control. Weeds growing on fence lines, farm roads, irrigation ditches, manure piles, in your stock yards and around farm buildings provide an annual nursery of weed populations. (See Table 2) Carried by wind, water, vehicular traffic and livestock, they travel with ease to infest "clean" land.
These "non-crop" weeds are also important habitat for insects and diseases which attack your adjacent crop. As an example, huge populations of the green peach aphid build up on common broad-leaved weeds such as lambsquarters, pigweed and mallow. This aphid can transmit over 100 plant viruses including potato leaf roll virus. Tomato Spotted Wilt Virus, a new and serious disease of greenhouse crops in south coastal B.C., can be spread to field grown vegetables by thrips. Creeping yellow-cress, an increasing weed problem in the Fraser Valley, is an important source of disease carrying thrips. Remember 1. Learn your weeds to properly select the right control strategies. Your local Ministry of Agriculture and Food office can assist you in identifying weeds.
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2. Rotate herbicides and cropping practices to break resistance cycles and shifts in weed types, to prevent soil microorganism decomposition of herbicides and to prevent soil residue buildups. 3. Don't use herbicides until weather and soil conditions are suitable as indicated on the label. 4. Solve your tough weed problems before seeding. 5. Be aware of and control weeds in areas adjacent to your cropland. Step 2. Planning the program Once you have properly identified the weed and determined the problem, the next step is planning. Draw a map of your operation, including non-cropped areas. Mark on the map crops that you are growing, cropping sequence and weed that are present. Determine if the weeds are caused by underlying factors such as poor drainage, poor fertility, pH, etc., and plan to correct these first. Obtain information on weed control strategies and write them on the map along with notes on timing of control operations. If chemical control is chosen you must ensure that the herbicide is registered for use on your crop and that the weeds you have identified are listed as controlled on the label. List all registered herbicides on your map, along with their cost per hectare (acre). Obtain information on potential environmental impacts. Information on chemical toxicity to fish and wildlife, herbicide use in or near riparian areas and recropping restrictions that might impact rotational crops are critical to deciding management options. Choose an appropriate management strategy based on effectiveness, cost and environmental considerations.
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Step 3. Implementing the program Once you have diagnosed the problem and planned your attack, you must now put the plan into operation. This is where the majority of mistakes are made! Accurate herbicide application saves money. Recent surveys in the U.S. have shown that 63 percent of growers had a 10 percent or greater application error when applying herbicides. Overapplying results in crop damage and a waste of money. Under-applying results in lower crop yields caused by poor weed control, and again therefore, a waste of money. Sprayer maintenance, particularly of the delivery systems, is crucial for accurate application as is sprayer calibration. If you don't know the exact output of your sprayer, you're only guessing at how much chemical to put in it. Soil preparation is also very important for effective weed control. Pre-plant incorporated and pre-emergence herbicides must be applied to a well worked, moist and smooth, but fairly firm seedbed, free of clods and trash to obtain uniform chemical distribution and to encourage good seedling establishment. If incorporating volatile products such as Eptam, Treflan and Eradicane, the soil should be warm and moist, but dry enough on the surface to obtain good mixing. Speed of incorporation is also critical and this will depend on the herbicide and incorporation machinery used. Generally, disc implement should be run at 7 to 10 km per hour; field cultivators at 10 to 13 km per hour. Lastly, timing as determined in your plan must be strictly adhered to. All too often, producers delay attempts at control until weeds are tall and smothering the crop. By this stage, the competitive damage to the crop is done and the weeds are too far advanced for effective chemical weed control. EARLY diagnosis and EARLY treatment are the keys to success.
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Step 4. Monitoring Success/Failure It is essential to review records to determine what worked and what didn't so that improvements can be made in subsequent programs. Monitoring should point to changes that may be necessary in crop or habitat management to prevent weeds from invading. Steps to Reduce Herbicide Use • • • • • • • • • • •
use herbicides only when weeds are in the susceptible stage use herbicides only when weather and soil conditions are appropriate for effective control use Wipe-on technology where appropriate for weeds growing above the crop use band treatments over the row and cultivation between rows selective flaming or steam treatment may be appropriate in some situations (more research needed) use winter cover crops to reduce winter annual weed seed production use rotary hoe and precision cultivators when possible properly maintain application equipment and accurately calibrate maximize competition from beneficial plants think weed PREVENTION! READ THE HERBICIDE LABEL BEFORE USE
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bluestem_big_flower
blue-eyed-grass.little.plant
blue-eyed-grass.little.flower
blue_vervain_plant
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blackgrassVop
blackgrass_flowerVop
black-eyed-susan.smallplant
black-eyed-susan.flowers.
177
black-eyed-susan.flower
blackberry.trailing.plant
blackberry.trailing.leaves
blackberry.trailing.berries
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blackberry.spp.berry
blackberry.canada.plant.
blackberry.canada.flower
birdsfoot.trefoil.plant
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Birdsfoot trefoil flower
Birch
Bindweed hedge youngplant
Bindweed hedge plant
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Bindweed young plant
Bindweed leaves
Bindweed leaf-flower
Bergamot plant
181
Beggarstick flower
Beggarstick
Bedstraw plant
Bedstaw flower
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CHAPTER 6
METHODS OF HERBICIDAL APPLICATION Practical study of various methods of herbicidal application and necessary precautions. Introduction : Use of chemicals for weed control offers great potential in crop production. It has been largely a post world war-II development. Apart from introduction of Dinoseb (1933), 2,4-D and MCPA(1945) it is now around 60 years since the first effective arsenic was marketed. In India, Sodium arsenate was used for the first time in Punjab to control Carthamus oxicantha while 2,4-D was first tested in 1947. but the chemical weed control struck deeper roots on a commercial scale in late 70’s. In India consumption of insecticides is more(75%) as compared to herbicide(13%),
fungicide(8%)
and
other
agro-chemicals(4%).
Herbicides market in India has grown about eight folds during last 15 years. For effective and efficient weed control, selection of proper method of application is more important. Herbicides are applied to the soil (Soil application) or to the foliage (foliar application) depending on the properties of herbicide, mode of action and selectivity, different
183
methods are adopted. Environmental factors, convenience and cost are the other factors that influence the choice of a correct method of application. An improper method of application can result in poor weed control and / or severe crop injury.
Objective: i)
To ensure the effective use of herbicide.
ii)
To save the non-target vegetation from herbicide.
iii)
To provide early season or zero day weed control.
iv)
To reduce the need for repeated intercultural operations during crop season.
v)
To control problematic weeds which can not be controlled effectively by other methods.
vi)
To control the weeds during adverse soil and climatic conditions.
vii)
To control the weeds of closely spaced crops without trampling.
viii) To control the weeds without any mechanical injury to the standing crop. ix)
To minimize the weeding cost, time and labour use.
Methods of herbicidal application: The herbicidal application can be grouped in the following waysOn the basis of time of applicationi)
Pre-planting application,
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ii)
Pre-emergence application,
iii)
Post- emergence application, and
iv)
Lay-By application.
On the basis of method of applicationA) Foliage applicationi)
Blanket spraying method,
ii)
Direct spraying,
iii)
Protected spraying, and
iv)
Spot treatment.
B) Soil Applicationi)
Surface application,
ii)
Sub surface application,
iii)
Band application, and
iv)
Soil fumigation.
The choice of a method to be effective for weed control depends upon the nature and properties of herbicide and the characteristics of target plants. Herbicides, in natural state, may be solid or liquid, volatile or non-volatile, soluble or no soluble. Herbicides are formulated in soluble powders, Wettable powders or in emulsifiable forms. To increase the biological effectiveness of herbicide adjuvants are added. These adjuvant modify the physical properties of herbicide and make it fit for easy application, long storage and biologically effective. Precautions to be taken while handling herbicides:
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Nearly all the herbicides are potentially dangerous, if they are used properly and recommended precautions are not observed. i)
Read the label on each container before using the contents and strictly follow the instructions there in.
ii)
Destroy the empty containers by burying them at least 18 inches deep in an isolated area away from water resources.
iii)
Apply the herbicides only at the time specified on the label. It is very necessary to observe the recommended intervals between treatment and pasturing/ harvesting of the crop.
iv)
Always consult the product label or technical bulletin before applying the chemical.
v)
Wear goggles, rubber gloves and other clothing as recommended on the label.
vi)
Guard against possible injury to near by susceptible plants.
vii)
The herbicide should be kept in a safe place (away from seeds, fertilizers, edible grains, cattle feed etc.) where children and other unauthorized person do not have access.
viii) The herbicides should never be stored on the farm and should be used just after purchase. ix)
Never use the herbicide from unlabeled containers or kept in such a container whose instructions have been mutilated.
Precautions to be taken during preparing solution: (i)
Read the available literature on or with the container and act accordingly
(ii)
Always make the solutions in glass or plastics containers.
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(iii)
The quantity of solution should be fixed according to the efficiency of sprayer used for the purpose.
(iv)
Add soap emulsion, or other adhesive substances to increase the viscosity of the spray material.
(v)
Care should be taken that during preparing the solution no part of the body may have direct contact with the herbicide. During this period the person using herbicide should wear goggles, rubber gloves and mask and adopt other protective measures.
(vi)
Always have soap and fresh water in the place of preparing solution.
Necessary precautions during use: (i)
Act as per instructions on the label
(ii)
Never try to identify the herbicides by feel or smell.
(iii)
Stop spraying operations at high wind speed, intense heat or when rain is just expected.
(iv)
Never try to blow clogged nozzle by mouth pressure.
(v)
Clean and wash sprayers carefully before and after use.
(vi)
Never work alone while handling the herbicides as well as their application.
(vii) Do not eat, drink, smoke or rub your eyes with hands during spray. (viii) Avoid sprays reaching the nearby water bodies. Reasons for toxicity symptoms of herbicides on crops.
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All the recommended herbicides are very safe for respective crops in which they are recommended provided they are used according to the recommended technology. Even recommended herbicides may show toxicity symptoms under certain situation such as 1. Wrong time of application: Application of herbicides too early then its recommended time may cause yellowing and necrosis of crop. Over dose of 2,4-D/ its application on very young crop may cause tubular leaves and deformed wheat ears. 2. Use
of
over
dose:
Application
of
higher
then
recommended dose is also responsible for stunting, yellowing and necrotic growth of crop plants. 3. Adoption of wrong application technology: Un- uniform application of herbicides not only harm the present crop but may also prove harmful for the succeeding crops due to residual toxicity. 4. Spray drift: Due to speedy winds on the day of spray, adjoining crops may be demaged. 5. Adverse climatic conditions: Due to heavy rains immediately after the application of herbicides, few root uptake herbicides may even demage the tolerant crops. 6. Due to non-adoption of recommended technology: With the use of un-approved herbicides, crop is damaged. For instance, wheat crop may be damaged with the use of
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metribuzin. Germination of wheat crop is adversely affected when seeds come in contact with triallate treated soil zone.
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Beautyberry
Bearberry plant
Bearberry flower
Bearberry berry
190
Bayberry plant
Bayberry berry
Barnyardgrass ligule
Barnyardgrass seedling
191
Barnyard grass seed head
Barley fox tail
Barley fox tailed
Avocado
192
Aster Spp.
Aster flat topped white
Aster flat topped white
Aster
193
Aspen
Angelica
Amaranth spiny
194
Amaranth grain
Alder seed head
195
CHAPTER 7
CALCULATIONS ACID EQUIVALENT (a.e.)—the theoretical yield of parent acid from an active ingredient. ACTIVE INGREDIENT (a.i.)—the chemical in a product that is responsible for the effects. Acid equivalent technically refers to that portion of a compound (herbicide) derived from an acid that can theoretically be converted back to the acid form. Since this theoretically convertible portion also carries the herbicidal activity, acid equivalent then becomes synonymous with a.i. If a compound is not derived from an acid then the portion with herbicidal activity is simply active ingredient, not a.e. Both a.e. and a.i. are generally expressed in kilogram (1000 g) per hectare (10,000 sq m) for either dry or liquid formulations. Rates of application are generally expressed in a.e. or a.i. in most publications and in weight of commercial product by chemical manufactures. Volume Rate --- amount of liquid (water) applied per unit area. The following refers to herbicide use: litres/ha High volume
675-1125
Medium volume
225-675
Low volume
56-225
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Very low volume
11-56
Ultra low volume
1-11 (use of concentrated,
undiluted,
oil-based formulation)
CALCULATION OF GR50 VALUES FOR WEEDS AND CROPS.
The concentration of herbicide required to inhibit plant growth by 50 per cent as compared to untreated plants (cf LD50). GR50 can be worked out on dry matter basis or on mortality basis. An ideal herbicide has very low GR50 values for weeds and very very high for crop .e.g. clodinafop has very low GR50 values for P. minor and very very high for wheat. With the help of these studies, the probable period during which resistance may develop in weeds can be estimated. These studies are conducted in plots or even in small plots. The herbicides for which GR50 values for are to be calculated, is applied at variable levels i.e. double than recommended (2R), R, ½ R, ¼ R, 1/8 R. a untreated treatment is also kept. For studying GR50 values of crops, more higher levels than recommended are kept. GR50 value can be calculated by using Probit analysis provided in software programme M-STAT by using either data on mortality or on dry matter. Basic GR50 value can also be calculated by using log-logistic analysis in which values of dry matter accumulation by weeds are assigned to Y-axis and log of doses are assigned toX-axis on graph to obtain a dose response curve. The mathematical equation used relating to response Y to dose X is given below. Y = f(x) = C + (D-C)/1 + exp [ b(log x)- log (GR50)] Where
197
C= Lower limit in the mean response (dry matter) at very high dose. D= Upper limit corresponding to the mean response of the control GR50 = Dose giving 50% response B= the slope of curve aroung GR50 value. Herbicide Application Techniques Herbicides are chemicals used to kill weeds. Unlike others pesticides, herbicides demand more skill in application. Proper application is very important aspect in herbicidal use. Due to improper application, herbicide treatment may be ineffective or it can cause serious damage to crop in which it was applied or to the neighbouring crops. For the safe and effective use of herbicide selection of proper equipment, technique, method are very important. While applying herbicides the following points should be considered. 1)
Equipment:
Knap sack sprayers are quite suitable for our
condition which can be carried on the operators back. Flatfan, flood jet nozzles are most suitable for herbicide application. 2)
Spraying pressure: Optimum pressure in case of Knap sack
sprayer to be maintained is 0.7 kg/cm2 to 3kg/cm2 . The output through the nozzle depends on the spraying pressure. 3) Agitation: It is important to prevent settling specially where suspensions of wettable powder are used. Due to settling there may be variation in concentration during spraying. Deflocculents for this purpose can be used. 4) Avoidance of drift: To avoid drift it is recommended to stop spraying when the wind is too strong (more than 10 km/hr). For wind
198
of 5-10 km/hr the height of the nozzles should be maintained as constant throughout spraying. The hormone type herbicides like 2,4-D are very toxic to some crops such as cotton, beans, tomatoes and cucurbits. The flatfan nozzle can be used at a pressure of 1 to 2 kg/cm2 . A non selective herbicide (contact) may be applied as directed spray by using hoods. 5) Calibration: Herbicides are selective to crops when they are applied at recommended dosages, they will be either harmful or of no use when applied at higher or lower rates than the recommended respectively. For this, calibration of the amount of herbicide and water to be applied and the speed of walking, pressure to be maintained, etc., are of very important. The calibration can be done by using the following calculation. Total distance traveled---d metres (say), time taken for traveling the distance d metres—t min., walking speed---- d/t, swath—X metre. Area covered in time t –( d X x) metre
Amount of solution discharged at the given pressure : L lit. Rate of discharge
: L/ ( d X x) sq m
Amount of solution required/ha at the given pressure
:
L____ X
10,000 dX x
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The readymade table of rate of discharge at a given pressure of 3 kg/ cm2 Walking
Swath width (m)
speed m/ sec
0.5
0.6
0.7
0.8
0.9
1.0
1.0
83.34 100.00 114.67 133.34 156.00 166.67
1.5
55.56 66.67
76.45
88.89
104.00 111.11
2.0
41.67 50.00
57.34
66.67
78.00
83.44
2.5
33.34 40.00
45.87
53.34
62.40
66.67
3.0
27.75 33.33
38.22
44.45
72.00
55.60
Calculation of actual amount of final product (formulation) based on recommendation in active ingredient/ha. Formula for the calculation of commercial product: Weight of chemical to be applied
X 100
Percentage of active ingredient present e.g. Fluchloralin (basalin 48 EC) is to be applied at the rate of 1.0 kg a.i./ha in groundnut as pre-plant incorporation. If the amount of water to be mixed is 600 lit/ha, calculate the actual amount of Basalin(48 EC) to be added to the water/ha. The active ingredient present in 1 litre of basalin: 480 gm So the amount of commercial product required is 2.08 lit. of formulation. So we have to mix 2.08 lit. of formulation (or) commercial herbicide (Basalin) with 600 lit. of water to spray per one hectare.
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In Acid Group Herbicides since it is the acid form that is responsible for killing the weeds, so here the a.i. will be in the form of acid, which is called acid equivalent. In case of phenoxy group the total a.i. includes amine part, sodium part or ester part of the 2,4-Dichloro phenoxy acetic acid where as acid equivalent means the 2,4-D acetic acid part. e.g. A 2,4-D herbicide on which it is written 40 % acid equivalent, 45% a.i. and 55% inert material. The recommended dose is 2kg/ha. How much herbicide is needed for 500 sqm as well as quantity of water required at the rate of 500 lit/ha. Amount of commercial herbicide required/ha
For 500 sq m
a.i. recommended X 100 acid equivalent present 2 X 100 = 5 lit. 40 5 X 500 = 0.25 lit 10,000
Water required for one ha----- 500 lit. For 500 sq m =
500 X 500 / 10,000 = 25 lit.
In the above example while calculating the commercial product acid equivalent is taken into consideration.
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How to find out acid equivalent? e.g. Find out acid equivalent of 2,4-D diethanol amine salt with 70% a.i.
a.i. X molecular wt. of 2,4-D acid Acid equivalent =------------------------------------------------------Molecular wt. of 2,4-D amine salt 70 X 221 = ----------------- = 47% 326 Calculation of commercial product required for band application e.g. Diuron with (80%) is recommended at the rate of 2 kg a.i./ha as pre-emergence spray, as band application. The distance between 2 rows is oe meter and a 20 cm band is required to be sprayed. How much is the quantity of Diuron required for band application as well as for usual overall soil application in 1000 sq m area (rectangular shape 1 mX 1000 m)
Quantity of commercial product required for overall soil
a.i. recommended =
application
--------------------------- X 100 a.i. present in the product
= 2/80 X 100 = 2.5 kg commercial product
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Quantity of commercial product required for band application
= Area X product required/ ha
width of band length of area in m X in m = ---------------------------------------------------- X 2.5 10,000
area in m X 2.5 = --------------------------10,000
0.2 X 1000 = ------------------------ X 2.5 = 0.05 kg 10,000
B Calibration of the pump Select any spraying equipment by keeping in view size of the farm, time of application of herbicide, facilities available, type of the soil, moisture holding capacity of soil etc. let us assume Knap-sack spray pump has been selected foe applying herbicide fitted either with flat fan or flood zet nozzle. Measure a small area and pour measured quantity of water into the container of the pump. Spray the plot with water and measure the left out water and work out the amount of water used for spraying a unit area. Then calculate the amount of water
203
required for spraying one acre. Do not change pump operator or nozzle while applying herbicide in the field. For uniform distribution of the chemical (a) the nozzles should be oriented in such a way so that the spray from each nozzle should not hit each other. Angle of 5 degrees of the spray jet diversion on the boom is recommended, (b) the height of the boom must be adjusted and maintained constant throughout the operation. Cleanliness The sprayer should be cleaned before and after use always. .The complex for of spray operations may be written as follow 1) Type of treatment (a) pre-plant incorporation (b) pre-emergence to weeds (or) crop (c) post-emergence to weeds alone (d) post-emergence to weeds and crop (e) directed 2) Chemical to be used 3) Concentration a.i./a.e. in the formulation 4) Quantity recommended in a.i./a.e./ha 5) Quantity of formulated chemical per ha and to given area 6) Name of the equipments 7) Nozzle number, size and type 8) Pressure at the time of operation 9) Quantity of water required for the given area 10) Special precautions to be observed if any General precautions to be observed in spray application
204
1) Avoid drift
2) Avoid hot Sun
3) Minimum of 24 hours rainfree period 4) Observe cleanliness 5) Use recommended protective clothing 6) Pour the balance of unused liquid in trench provided.
205
CHAPTER 8
EVALUATION OF HERBICIDE EFFECTS Before evaluation is undertaken, the following steps should be done: 1) Walk over the entire test area to get an idea of the over all results, including any change in crop growth or weed population in different parts of the trial ( Is the absence of weeds or crop due to herbicide treatment or to poor viability of crop-seed, damage by insects/diseases ? ). 2) Observe the control plots closely. Note crop and weed population density, to serve as basis for evaluating population reduction in treated plots. 3) Perform evaluation without knowledge of the treatments in each plot, except the control plot, to do this evaluate the trial moving from back to front, so that plot markers cannot be read. 4) Compare results in each replication and double check to make sure that any case of wide variation between replication is due to treatment and no other cause. Do this before leaving the field. If the results of two replications differ significantly, re-check their evaluation.
206
Evaluation Methods 1) Quantitative method: Count the number of weeds per unit area (species-wise), measure height, weight of samples and yield. Yield is taken of crop grain and straw. This method is quite accurate but is time consuming. 2) Qualitative method: This method follows arbitrary scale to measure per cent control (stand reduction) and growth reduction of surviving plants. Crops and individual weed species may be rated separately. Per cent cover by weeds is often taken also, particularly those species which produce rhizomes. The European weed research council rating system FORM---A Weed response Rating
% weed control
Verbal description
------------------------------------------------------------------------------1
100
Completely destroyed
2
99.0 --- 96.5
Very good control
3
96.5 --- 93.0
Good control
4
93.0 --- 87.5
Satisfactory
5
87.5 --- 80.0
Just satisfactory
6
80.0 ---
70.0
Unsatisfactory
7
70.0 ---
50.0
Poor
8
50.0 ---
01.0
Very poor
9
0
As untreated
-------------------------------------------------------------------------------
207
FORM --- B Rating
Crop
response Verbal description
% crop injury 1
0
No reduction or injury
2
1.0
----- 3.5
Very slight discoloration, ect.
3
3.5
------ 7.0
More severe, but not lasting
4
7.0
------ 12.5
Moderate and more lasting
5
12.5 ------- 20.0
Medium and lasting
6
20.0 ------- 30.0
Heavy
7
30.0 ------- 50.0
Very heavy
8
50.0 -------- 90.0
Nearly destroyed
9
100
Completely destroyed
Regarding toxicity to crop usually the toxicity is reflected in the grain yields or if the toxicity is apparent, counts of crop plants at different stages of crop growth will give clear picture of the toxicity to the crop. 3) Listing relative tolerance and susceptibility. Another simple method is to simply list the species that, in the opinion of the evaluation, is tolerant, slightly tolerant suscepticle, or very susceptible to each of the herbicide treatments.
Evaluation of herbicide effects The efficacy of an herbicide can be assessed by the following methods ( based on weed index):
208
X -- Y Weed index = ------------ X 100 X Where X—yield from wed free plots Y—yield from treatment plots
Lesser the weed index better is the efficiency of that herbicide, we can also compare the efficacy of two herbicides with the help of weed index. Ex. A weed free plot of maize has given yields of 1500 kg/ha, where as atrazine and simazine treated plots have given yields of 1400 kg and 1450 kg/ha respectively, calculate weed index and give which herbicide is better in the two ? 1500-- 1400 1) Weed index for atrazine = -------------------------- X 100 = 6.66 1500
1500-- 1450 2) Weed index for simazine = ----------------------- X 100 = 3.33 1500
Since the weed index is less for simazine, simazine is better than atrazine.
209
Based on weed control efficiency X–Y Weed control efficiency = --------------- X 100 X Where X – Dry matter production of weeds in unweeded plot Y—Dry matter production of weeds in treatment plot Higher the weed control efficiency better is the herbicide. e.g. In a weed experiment in peas, dry weight of weeds in control plot was 620 kg/ha whereas for x and y herbicides, it was 230 and 360 kg/ha respectively. Find out which herbicide is better amongst two ?
620--230 1) Weed control efficiency for x = -------------- X 100 = 62.9 620
620--360 2) Weed control efficiency for x = -------------- X 100 = 41.9 620
Since the weed control efficiency is higher with x, hence it is better than y.
210
Based on herbicide efficiency index (HEI) (YT-YC) x 100 YC HEI DMT x100 DMC YT – Yield from treatment YC – Yield from control DMT – Dry matter of weeds in a treatment DMC – Dry matter of weeds in control
211
CHAPTER 9
SOME USEFUL INFORMATION WEED- SEEDS: 1 IDENTIFICATION CHARACTER S.No. Common name Botanical name Family
I. Fruit:
Shape
Colour
Size
II Seed: 1. External morphology: Shape--Colour--Size---2. Surfaces: Smooth
Glossy
Dull
Pittings
Grooves Sculpturing
3. Attachment scar (Hilum) Shape--Size---Position---4. Additional features: 212
Rough
Surface
Wings
Pappus
Spines
5. Internal morphology: Size of embryo--Shape of embryo--Position of embryo---Endoserpm-----Cotyledon-----Seed Coat------6. Germination behaviour: 1. Temperature---2. Substrata----3. Duration-----4. Special requirement: III. Seedling Morphology: Cotyledon shape etc. First leaf----Second leaf---Hypocotyl----Roots----Coleoptile---
213
Awans
Hairs
2.
METHODS
AND
PROCEDURES
ADOPTED
IN
COLLECTING DATA IN WEED CONTROL TRIALS Minimal Sample Area It is a common practice to determine the ‘minimal area’ of the community, which is defined as smallest area on which the species composition of the community in question is adequately represented. This smallest area gives an indication of the quadrat size that should be used. In contrast, where the emphasis is on sampling the quantitative variation of species within large communities defined only by dominant species, the idea of representative species composition is commonly reduced to certain quantitative measures of the more abundant species only. Instead of using a few large; minimal area’ quadrats or plots, the sampling is spread over each vegetation segment as much as possible in the form of small quadrats or point samples. The minimal area depends on the kind of community and varies within wide limits. The structure of a community can be studied under two heads, viz: (1) Analytic, and (2) Synthetic. The analytic characters are again of two types, viz. (a) Quantitative, which includes density, abundance, frequency and dominance, while other (b) Qualitative, which includes sociability, vitality, periodicity and stratification. On other hand synthetic characters include presence, constance and fidelity of components which may be computed from analytical characters of several stands of a community.
214
The analytical characters are determined by means of a three main sampling units—area, line and point, as employed in quadrat transect and point methods, respectively. Quadrat Method Quadrat method is actually the sample-plot method. In fact quadrat is a sampling unit which has an area of definite size, which may be circular, rectangular or square in shape. The kind of quadrat depends upon the objective and accordingly it may be list, count, chart, clip, permanent and denuded. The list quadrat gives merely a list of species present in the quadrat. In count quadrat, in addition to listing, number of individual plant of each species is also counted. Chart quadrat is used for details and scale recording of growth and distribution of species. With the help of ‘Pantograph’ and ‘Planimeter’ the accurate measurement is done. The chart quadrat may be made a permanent quadrat, where periodic readings are taken. In clip quadrat the vegetation is clipped from a quadrat. This is done at ground level or at various heights. The clipped matter is then determined in terms of fresh weight or dry weight. For studying seasonal variations in field, periodic clipping is done. In the denuded quadrat the vegetation is first removed by burning, flooding, salting, covering, scraping or by excavating the top of the ground and then studying the details when the vegetation in quadrat gets regenerated. Since the assemblage of plants in a community is largely heterogeneous, the determination of size and number of quadrats is necessary for adequate sampling.
215
Size of Quadrat With a piece of string and three nails ‘L’ shape structure in the fields is formed. Thereafter using another piece of string and a nail, an area of 10 X 10 cm is differentiated. All the plant species present in the area are recorded. Then the sample area is enlarged to 20 X 20 cm, 30 X 30 cm and so on, in each enlargement the additionally occurring species are listed separately. The sample area is increased until the species added to the list become very few. A graph is then plotted with sizes of quadrat on X-axis, and corresponding number of species on the Y-axis. This results in a species-area-curve. The minimum size of quadrat is the sample area at which the initially steeply increasing curve becomes almost horizontal. Vegetation Sampling It was suggested that a rectangular quadrat measuring 1X1 m is sufficient to represent the composition of an agricultural field. Quantitative Vegetation Analysis The first step in quantitative vegetation analysis is to determine the importance value ( I.V.) of species from each quadrat. This suggests the dominance of that species over others in its community. The importance value is based on fresh weight of the standing biomass of each species.
Wa I.V. ( % ) =--------- X 100 Wt
216
Where Wa is the fresh weight of a species and Wt is the total fresh weight of all species in a given sample plot. Florisitic Composition The dominant weed in a particular area can be expressed based on its importance values in relation to other weed species importance value existing in that area. Importance Value Index (IVI) In order to express the dominance and ecological success of any species with a single value only the concept of importance value index(IVI) has been developed. The IVI is defined as the sum of relative density, relative frequency and relative dominance. The relative density, relative frequency and relative dominance are calculated by the following formulae.
Number of individual of a species 1. Relative density ( RDe)= ---------------------------------------- X 100 Total number of individuals
Frequency of a species 2. Relative frequency (RF) = --------------------------------------- X 100 Sum frequency of all species Number of quadrats of occurrence of a species Where frequency of a species =-------------------------------------------Total number of quadrats
217
Dominance of a species 3. Relative dominance (RDo) = --------------------------------- X 100 Dominance of all species
Canopy cover of all species Where dominance of a species = ---------------------------------------Total sample area
Canopy cover denotes the area covered by each species when it is viewed from above.
RDe + RF + RDo IVI = ----------------------3 3.
Study of herbicide-label information
Significance of symbols on the label Several signal words or symbols based on the toxicity of the product are required by law to group them into respective categories of toxicity. There are 4 categories of toxicity and each of which is indicated by an appropriate symbol and signal as follows:
218
Toxicity
Acute
Category
oral toxicity
Colour
Signal word
Warning
of
required on
symbols on
triangle
label
the label
LD 50 mg/kg 1.Extremely
0-50
Toxic
Bright
Word
Skull and
red
‘POISON’
cross bones
printed
in
red 2. Highly
51-500
Toxic
Bright
Word
yellow
‘POISON’
___
printed in red 3.
501-
Bright
Word
Moderately
5000
blue
‘Danger’
___
Toxic 4. Slightly Toxic
5000 Bright green
Word
‘
____
Caution’
Precautions 1) Read all the information given on the labels of the containers. 2) Note the symbols written on the labels very carefully.
219
Materials Required i) Empty herbicide containers bearing labels. ii) Sample labels of various types of commercial herbicides. Procedure Examine a few commercial herbicide containers and make a list of all types of information given on the labels. Observations The student should note down the information available on the labels against each item in the following table. ITEM HERBICIDE 1 I Chemical name II Common name III Trade name IV Manufacturer’s address V Percentage of active ingredient VI Percentage of carrier, filler and
220
2
3
4
adjuvant VII Difference between different products containing the same active subgradient VIII Net content, if given IX.Treatment
for
accidental
exposure or poisoning X Date of manufacture XI. Date of expiry XII. Misuse statement, if any XIII. Direction for use, if any XIV. Storage and disposal of
the
product, if any XV. Warranty statement, if any XVI. Precautionary statements,if any
221
XVII Name of the crops for which the herbicide s recommended XVIII. Any other information 4.
PRACTAL APPLICATION OF HERBICIDES
Modern chemical methods of weed control with herbicides offer the most pratical, effective and economical means of reducing weed competition, crop losses and production costs. In the past, herbicides other than 2,4-D and MCPA have been regarded as too costly in many countries. This situation has been changed due to the introduction of new formulation of herbicides. Herbicides are presently available as granular materials ready for direct use, or as emulsifiable concentrates (EC), wettable powder (WP) and water soluble powder(WSP). However, to use these inexpensive chemicals to eliminate weeds in rice or any crop effectively, we must understand the following three general precautions. 1) Apply herbicides at right time. 2) Apply herbicides accurately because inadequate amounts give unsatisfactory weed control and excessive rates may injure the crop.
222
Observation to be recoded before spraying of herbicide Field history Crop grown earlier
:
Irrigated or rainfed
:
Cultural practices for current year
:
Fertiliser rates and schedules
:
Details of insect and disease control measures chemicals used with schedules
:
Crop
Spacing
Name and variety
:
Rows :
Seed rate
:
Plant to plant in row :
Weather at application Air temperature
:
Soil temperature:
Wind speed
:
Wind direction :
Relative humidity
:
Sunshine rating
: ( (
) very bright
(
) partial cloudy (
223
) bright ) cloudy.
Rainfall : Daily for 1 week after application : Weekly for 8 week after application : Monthly till completion of experiment : Weeds :
Name and stage of growth of weeds present at the time of
treatment in the order of dominance. 1. 2. 3. 4. 5. 6. Remarks : Note the method of planting of crop, uniformity of weed growth, methods of evalution etc. 5.
DIFFERENT TYPES OF SURFACTANTS
The primary classes of surfactants are anionic, cationic, nonionic and amphoteric. Anionic and cationic surfactants ionize in water and owe their surface active properties to their anion and cations respectively. Nonionic surfactants do not ionize in acqueous solutions. Amphoteric surfactants acts as either anionic or cationic surfactants
224
depending on the acidity of the solution. Most commonly used agricultural surfactants are nonionic. They are easy to use, non-toxic and are not affected by hard water. Wetting agent A wetting agent is added to a herbicide formulation to spread the spray droplets over the surface of the leaves. It increases the moistening ability of the spray. The examples are Chikawet, syd-50 etc. Emulsifiers The oil is mixed with water to form emulsion. If this mixture is allowed to stand the oil and water will separate. To decrease the tendency to separate a third material is added. This is called the “emulsifying agent or emulsifier”. The examples are NOIGEN, Emulsol-KP 66, Emulsifier-UD etc. Dispering agents These substances reduce the cohesion between the like particles. Some dispersing agents are good wetting agents and suspending agents. The examples are Tamol-DN, NNO Glutex of Unisperse etc. Spreaders Wetting agents and spreaders are closely related. The tendency of wetting agents to reduce surface tention also increase the spreating. The examples are Chikawet, syd-40, Dedenol etc.
225
Sticking Agents Sticking agents cause the herbicide spray to adhere to the sprayed surface. Teopol, Triton-AE, Sandovit etc. Surfactants probably have four important effects on the plants. 1) They favour uniform spreading of the spray, or uniform wetting of the plant. 2) Spray droplets usually stick to the plant and there is less bounce off. 3) The chemical spray is brought into inmate contact with the plant surface. Droplets do not remain suspended on hairs, scales or other projections. 4) The surface active agents may alter non-plor plant substances to polar substances so that the plant readily absorbs the chemical.
226
Table : Analysis of quantitative characteristics in a form of model Plant
No. of individual
Total
No. of
No. species
Total
Quadrat
Quadrat number of indiv-
Abun-
Density
No. dance of Of
quadrat
occurence iduals
Amaranthus
studied
1
2
3
4
5
6
7
8
9
10
10
-
15
-
10
5
8
10
10
9
77
8
10
9
8
5
9
8
7
10
4
-
9
5
12
69
9
10
7
7
-
6
6
-
5
-
8
-
4
5
34
6
10
6
3
33
-
-
4
-
8
-
3
-
25
46
5
10
9
5
Virdis Boveria diffusa Celosia argentea Cyperus sp. and so on
227
CHAPTER 10
WEED SEED BANK Soil is a rich reservoir of seeds. Seed bank in the soil is the primary source of new infestations of weeds each year. The species composition and density of weeds in soil vary greatly and are closely linked to the cropping history of the land. The size of seed bank in agricultural land ranges from near zero to as much as 1 million seed m2
. Seed bank are generally composed of numerous species belonging to
three groups. The first includes a few dominant species accounting for 70 to 90 % of the total seed bank. These species represent most of the weed problems in a cropping system. A second group of species, comprising 10 to 20 % of the seed bank, generally includes those adapted to the geographic area but not to current production practices. The final group accounts for a small percentage of the total seed and includes recalcitrant seeds from previous seed bank of the previous crop. This group undergoes constant change due to seed dispersal by humans, other animals, wind and water. Quantifying weed seeds in the soil seed bank is of particular intrest to ecologists and weed scientists, as it enables them to determine
228
the potential density, intensity and diversity of weed infestation in a particular crop or non-cropped area. This information is useful in understanding and predicting the fate of weed seeds in the soil and designing
effective,
viable
and
economic
weed
management
programmes. A number of methods have been described in the past for collecting soil samples and then extracting weed seeds, these include using augers, metal tubes, plastic liners and a vacuum system for collecting soil samples and adopting the technique of seving, flotation in high-density solutions and centrifugation for extracting and separating the weed seeds. Generally weed seeds restrict to the plough layer of the field and sometimes these may penetrate deep through the cracks which may develop in some soils. For these studies vertical soil samples are taken with suitable implements before sowing the crop or after its harvest. These soil samples are taken from different soil zones to find out their pattern of distribution. Then the samples on weight or volume basis are placed in the germinator at an ideal temperature favouring the germination of the target weed (S). these soil samples can also be placed at room temperature (suitable for germination of target weeds) in a shallow (1 to 2 cm depth) in pots or pettry dishes or plastic plates. The samples are kept moist and germination of weed seeds are recorded.
229
Samples from crop
Soil depth (cm)
Rice
0 – 7.5
No. of seedlings of
7.5 – 15.0 Maize
0 – 7.5 7.5 – 15.0
Brown
0 – 7.5
sarson 7.5 – 15.0
Table : Prolific seed production by weeds Type of weeds
Seeds/plant
Perennials
16,629
Biennials
26,600
annuals
20,832
Table: Seed production capacity of individual weeds and wheat S.No. Name
Seeds /plant
1
42,758
Echinochloa colonum
2
Trianthema
10,000
portulacastrum 3
Amaranthus
20,000
spinosus 4
Digera muricata
230
25,000
5
Euphorbia hirta
4,000
6
Acalypa indica
10,000
7
Amaranthus
10,000
viridis 8
Tridax
500-1500
procumbens 9
Celosia argentea
11,812
10
Phyllanthus
1,000
maderaspatensis 11
Leucas aspera
5,000
12
Argemone
20,000-30,000
mexicana 13
Parthenium
10,000
hysterophorus 14
Striga lutea
30,000-75,000
15
Orabanche
1 Lakh
cernua
231
5(&200(1'$7,216 $11(;85( $11(;85(, Sl. No.
1.
2.
Crops
Maize
Soybean
Herbicide
Dose kg (ha-
Stages of
1
application
)
Atrazine
1.0
Pre-emergence
Alachlor
2.5
Pre-emergence
Alachlor
2.5
Pre-emergence
Pendimethalin
1.0
Pre-emergence
Fluchloralin
1.0
Pre-plant
Trifluralin
1.0
incorporation
Metribuzin
0.35
Pre-plant incorporation Pre-emergence
3.
Urd, moong,
Alachlor
2.5
Pre-emergence
cowpea, arhar
Pendimethalin
1.0
Pre-emergence
Fluchloralin
1.0
Pre-plant
Trifluralin
1.0
incorporation
Metribuzin
0.35
Pre-plant incorporation Pre-emergence
4.
Rice nursery
Thiobencarb
1.0
Pre -emergence
5.
Transplanted
Butachlor
1.5
Pre-emergence
rice
Anilofos
2.4
Pre-emergence
Pretilachlor
1.0
Pre-emergence
Thiobencarb
1.0
Pre-emergence
0.004
Post-emergence
Almix
232
6.
Wheat
Oxadiargyl
0.1
Pre-emergence
2,4-D
0.5
Post-emergence
Isoproturon
1.0
30 days stage
Clodinafop-
0.06
30 days stage
propargyl
0.025
Sulfosulfuron
0.09
30 days stage
Fenoxaprop-p-ethyl
1.0
30 days stage
Pendimathalin
0.5
Pre –emergence
0.004
35-40 days stage
2,4-D Metsulfuronmethyl 7.
30-35 days stage
Gram, pea,
Pendimethalin
1.0
Pre –emergence
lentil
Fluchloralin
1.0
Pre-plant
Trifluralin
1.0
incorporation Pre-plant incorporation
8.
Potato
0.5
Paraquat
Post to weeds before emergence of potato
9.
Sugarcane
Pendimethalin
1.05
Pre –emergence
Metribuzin
0.35
Pre –emergence
Atrazine
2.0
Pre –emergence
Metribuzin
1.0
Pre –emergence
2,4-D
0.5
Post-emergence
233
$QQH[XUH,, ,QWHJUDWHG:HHG0DQDJHPHQW5HFRPPHQGDWLRQV 7UDQVSODQWHGULFH
Use rice seeds free from weed seeds for raising nursery Use wet bed method for raising rice nursery Irrigate rice nursery field 8-10 days before seeding to stimulate weed seed germination, which may be destroyed during puddling
Spray anilofos at 0.4 kg ha-l or thiobencarb at 1.0 kg ha-l when first leaf of rice has turned green
Up root manually the weeds escaping after herbicide spraying to check their transfer to main field during transplanting
Summer ploughing of main field to destroy weeds and expose soil Properly level and bund to facilitate proper puddling and retention of water in the transplanted field. This will help in reducing weed emergence
Transplant healthy seedlings free from weed seedlings, at least two seedlings per hill at proper spacing early in the season to optimize plant
Population which would provide competitive advantage to the crop against weeds
Apply butachlor at 1.5 kg ha-l or anilofos at 400 g ha-l or pretilachlor at 1.0 kg ha-l or oxadiargyl at 100 g ha-l as pre emergence to weeds after transplanting. If required depending upon weed infestation and species apply 2,4-D at 500 g ha-l or aImix at 4 g ha-l as post emergence to control sedges and broad leaf weeds or do one manual weeding
234
Try to maintain standing water 3-4 cm in transplanted field at least during early stages to check weed emergence 6XJDUFDQH
After emergence of sugarcane irrigate at 40-45 days stage and do hoeing to destroy emerged weeds at this stage followed by spray of atrazine at 2.0 kg ha-l or metribuzin at 1.0 kg ha-l before emergence of weeds
Irrigate field as and when required to maintain proper soil moisture 2,4-D at 500 g ha-l may be sprayed to control Ipomoea spp In ratoon crop do mulching with the available trash in field after harvest of main crop 6R\EHDQ
Spray alachlor at 2.5 kg ha-l or pendimethalin at 1.0 kg ha-l as pre emergence or fluchloralin at 1.0 kg ha-l or trifluralin at 1.0 kg ha-l as PPI or metribuzin at 350 g ha-l as pre-emergence. This will provide effective control of annual grassy weeds.
Do manual uprooting of left over weeds and broad leaf weeds not controlled by these herbicides. 3RWDWR
Do mulching with available materials immediately after potato planting In case of non-availability of mulching material, spray paraquat at 500 g ha-l when weeds have emerged but potato emergence is not more than 5 %. It should be followed by earthingup at appropriate stage
Pendimethalin at 1.0 kg ha-l or metribuzin at 350 g ha-l may be applied as pre-emergence followed by manual weeding and earthingup at appropriate stage.
235
APPENDIX-I Conversion Table To convert Acres (ac)
To
Multiply by
Square
meters
4,048.5
2
(=sq.m or m ) Hectare (ha) Acre feet (Ac Cubic
0.405 meter
1,219.85
3
ft)
(=cu. m or m ) Hectare meter =
0.122
(ha.m) Litres of water Cubic feet
3
Cu. m (=m
Litres of water Qusec
Qumec
(Cubic
1.23 million 0.028 28.4 0.028
meter per sec) Cubic
meters Weight of water
(cu.m)
(kg)
1,010.7 0.0001
ha.m Feet (ft)
Centimeter (cm)
30.48
Meter (m)
0.305
Gallons (gall)
Litres of water
4.546
Gal./Qusec
Litres/cumec
162.3
236
Litres/ha (1 ha-1)
Gal./ac
Gram per litre Ppm
9.35 1,000
(gm/lt.) Grams (g)
Kg
0.001
ha.
Square
rods
400
Weigh of water
10.11
2
(=Rd ) ha.m
in kg
million
Inches (in)
Cm
2.54
Litres
Kg of water
1.011
Miles
Km.
1.609
Ounces (oz)
Gm.
28.35
Pounds
Gm.
453.6
Kg.
0.454
Ponds/ cu sec
Kg/cumec
16.21
Ponds/ac
Kg/ha (=kg ha-1)
1.12
Ponds/ac ft
Kg/ha m of water
3.721
-1
Kg/L (=kg L )
Pounds/gal
Per cent solution
0.12 1.0
g/sq. cm (=g cm2)
70.31
per g/cu m (=g m3) of
1.011
Pounds/sq.in (psi)) Parts
237
million (ppm)
water Kg/ha m of water
10.11
Per cent solution
0.0001
Parts pr billion ppm
0.000001
(pp) Per cent
Ppm
10.000.0
Pints
Litres of water Cups
0.44 2
Tea spoon full
32
Quarts
Lires of water
1.136
Rods
Meters
Sq.in
5.03 2
sq.cm (=cm ) 2
Sq. ft
sq.m (=m )
Sq. mile
sq.km (=km2)
6.45 0.093 2.6
ha.
260.0
Sq. km
ha.
100.0
Sq. rods
ha.
0.00253
sq.m (=m2) -1
Tones per acre t/ha (t ha ) (T/A)
238
25.29 2.47
APPENDIX-II Significance of symbols on the herbicides label Toxicity
Acute
Colour
Signal
Warning
category
oral
of
word
symbol
toxicity
triangle
required
on
LD50
(bright)
on label
label
Red
Poison
Skull and
the
(mg/kg) Extremely
0-50
toxic
cross bones
Highly
51-500
Yellow
Poison
Bones
Blue
Danger
-
Green
Caution
-
toxic Moderately 501toxic
5000
Slightly
5000
toxic
239
APPENDIX-III Some firms dealing with herbicides and their application equipment in India 1.
Agromore Ltd., Mysore Road, Bangalore -560026
2.
Alkali and Chemical Corporation of India Ltd., Post Box No. 107, New Delhi, or 34 Chaurangi Road, Calcutta 700016
3.
American Spring and Pressing Works Pvt. Ltd., P.O. Box 7602, Malad West, Bombay - 400 064
4.
BASF India Ltd, May and Baker House, Sudan kalu Ahire Marg, P.O. Box 19108, Bombay- 25
5.
Bayer (India) Ltd., Alps Building, 56Jan Path, New Delhi- 110 001
6.
Bharat Pulverising MilIs Pvt. Ltd., Hexamer House, Sanjay Road, Bombay- 400 025
7.
Burmah ShelI, P.O. Box 688, BalIard Estate, Bombay- 400 010
8.
CIBA-Giegy ofIndia Ltd, Khetan Bhawan, 14 Jamesh Talu Road, P.O. Box- I 10I4,Bombay-20
9.
Crop-Aid (India) Pvt. Ltd., 118 Netaji Subhash Road, Calcutta700001
10.
Cyanamid India Ltd., 254-0-2, Dr. Annie Besant Road, P.O. Box99,Bombay-400 025
11.
Escorts Ltd, 19/6 Mathura Road, Faridabad (Harayana)
240
12.
ESPI Agricultural Machinery Pvt. Ltd., Plot No.270, Sector 24, Faridabad (Haryana)
13.
Essco Standard India Pvt. Ltd., 17 Jamdeshji Tata Road, Po. Box355, Bombay-400 001.
14.
Excel Industries Ltd., 184 - I87, Swami Vivekanand Road, Jageshwari, Bombay-400102.
15.
Gharda Chemicals Ltd.,48 HilI Road, Bandra (W), Bombay-400 050
16.
Gujarat Agri. And Chemical Syndicate, Ahmedabad.
17.
Hico Prbdu~ts Pvt. Ltd., Mugal Lane, Mahim,Bombay-400 016
18.
Hoechst India Ltd, 3/1, Ashaf Ali Road, P.O. Box-7065, New Delhi-I 10 002
19.
ICI India Ltd., Agrochemical and Pharmaceuticals Division, Khaleeti Centre, Madras-500 008
20.
Imeckmex India Ltd., Grescent House, Walchand Hira Chand Marg, Bombay - 400025
21.
Indofil chemical Ltd., Nirlon House, Dr. Anne Besant road, Bombay-400 025
22.
Moscot Agro-chemicals Pvt. Ltd., Banglore-560 058.
23.
May and Baker (India) Ltd., P.O. Box-9150, Bombay-400 025
24.
Monsanto Chemicals of India Ltd., Wakefield House, I I-Sprott Road, P.O. Box-584, Bombay-18
241
25.
National Organic Chemical Industries Ltd.,(NOCIL), Mafat Lal Centre, Nirman Point, Bombay- 18
26.
Pesticides (India) Ltd., P.O.Box-20, Udaipur
27.
Rallies India Ltd., Rallies House, 21 OS Marg, Fort, Bombay400001
28.
Sandoz (India) Ltd., Agrochemical Division, Dr. Annie Besant Road, P.O. Box-6596, Wadi, Bombav.400018
29.
Tata Chemical Ltd., Bombay House, 24 Bruce Street, Bombay
30.
Velsuol Crop oflndia,J.30, South Extension, New Delhi-I10049
31.
Voltas Ltd., AIPD, 19, J N Heredia Marg, Ballard Estate, P.O.Box-900, Bombay-400038
242
APPENDIX-IV Herbicide formulations available in India Herbicides
Trade name (Formulation)
Alachlor
Lasso 50 EC Alachloro 48 EC
Atrazine
Atrataf 50 WP
Anilfos
Taguard 30 EC
or
Arozin 30 EC
Anilophos
Aniloguard 30 EC Rice 30 EC
Butachlor
Arochlor Machete 50 EC Machete 5G Butanex Rasayanchlor Lambaste Pillarset Delchlor 50 EC Delchlor 5G
Benthiocarb or
Saturn 50 EC
Thiobencarb
Saturn 10 G
Gyanazine
Bladex
243
Chloramben
Amiben
Cyclocydim
Sethoxydim
Dichlofop methyl
Illoxan Heolom
Difenzoquat
Avenge
Diuron
Hexuron 80 WP Agromex Diuron 50 WP
Dalapan
Vegfru dalapan Tafapon Dalapon Hexapon 80 WP
Fluchloralin
Basalin 45 EC Basalin 48 EC
Fluazifop-p
Fusillade 12.5 EC
Flamprop
Mataven Suffix plus
Glyphosate
Glycel 41% SL
(Isopropylamine) salt
Round-up
Isoproturon
Arelon 50 WP Arelon 75 WP Vegfru Taurus 50 WP Nocilon 50 WP
244
Graminon 50 WP Belgran Tolkan Hytane Ronak 50 WP Delron 75 WP Linuron
Linuron
Metribuzin
Sencor
Metolachlor
Dual 500 EC Dual 720 EC
Metoxuron
Dosanex 80 WP
Methabenzithiazuron
Tribunil 70 WP Ambinil 70 WP
Nitrofen
Tok E-25
Oxyfluorfen
Goal 23.5 EC Goal 0.35 G
Propanil
Stam F-34
Pendimethalin
Stomp 30 EC
Paraquat (dichloride)
Gramoxone 20 EC Gramuron Weedol Sweep
245
Simazne
Tafazine 50 WP
2, 4-D Ethylester
Agrodone concentrate 48 Agrodone 18 WP Agrodex G Knockweed 18 EC Knockweed 36 EC Knockweed 4G
Dimethylaine
Agrodar 32 Agrodar 96 Knockweed 72
Sodium salt
Agrosodium salt Knockweek 2, 4-D Fernoxone WP
246
APPENDIX-V Reference Books on Weed Science. Crafts, AS., 1975, Modem Weed Control. University California Press, California. Gupta, O.P. 1984, Scientific Weed Management- Today and Tomorrow, Publishers and Printers, New Delhi, India, Joshi, N.C. 1984. Manual of Weed Control (revised and enlarged edition) Research Publication, Delhi, India. Khuspe, V. S. et al.1982. A compendium of Indian Weed Science Research (Vol. I & II), Metropolitan Book Co., New Delhi. Klingman, G.c.1981,Weed Science: Principles and Practices, John Wiley and Sons, Inc. N. York. Kondap, S. and Upadhyay,UCI985, A practical Manual of Weed control Oxford & IBH Publishing Co., India. MandaI, R.C, 1990, Weeds, Weedicides, and Weed Control: Principles and Practices, Agrobios India, behind Nasrani cinema, Chopsani road, Jodhpur- 342 002. Gupta, O.P.1999,Weed Management: Principle and Practices, ibid. Rao, v.S. 1983, Principles of Weed Science. Oxford and IBH Pub. Co., New Delhi. Subrahmanian, S. et at. 1991. All about Weed Control. Kalyani Publishers Ludhiana, India.
247
Somani, LL1992. Dictionary of Weed Science. Agro-tech Publishing Academy, Udaipur. Common journals of weed Science1.
Indian journal of Weed science-Indian society of weed science Department of Agronomy, Himachal Pradesh Agricultural University Palampur, RP, India.
2.
PANS-
Tropical
pesticides
research
head-
guaners
and
information unit London, U.K. 3.
Tropical pest management - Central for oversees pest research, college House, wreghts lane, London, W8, 5~.U.K
4.
Weed abstract- common wealth Agricultural aureux, fasnham royal, UK.
5.
Weed Research- European weed science society, Blockwell scientific. Publication, oxford, UK
6.
Weed Science - Weed science society of America 113, North Neil street, champaign, Illinois, USA
7.
Weed Technology- Weed science society of America 113, North Neil street, champaign, lllinois, USA
8.
Weed Today- Weed science society of America 113, North Neil street, champaign, Illinois, USA
248
APPENDIX-VI Residual limit of herbicides on different crops Herbicide
Crop
Maximum residue limit (PPM)
Alachlor
Atrazine
Butachlor
Dicamba
Groundnut
0.05
Sorghum grain
0.10
Sorghum fodder
1.00
Cotton seed
0.06
Cotton forage
8.00
Sorghum and cotton grain
0.25
Sorghum and corn forage
15.0
Sugarcane
0.25
Wheat grain and straw
0.25
Rice bran
0.50
Rice hull
1.00
Rice rough
0.50
Rice straw
3.00
Corn
0.50
Sorghum
3.00
Wheat
0.50
Sugarcane
0.10
249
Diurn
Cotton seed
1.00
Sugarcane
1.00
Banana
5.00
Cotton seed
35.0
Sugarcane
0.10
Soybean
1.00
Maize
10.0
fop Cotton seed
0.10
Dalapan
Fuazi butyl
Soybean
Fluchloralin
Cotton
1.00 seed,
pod
0.05
vegetable, groundnut, soybean
and
sunflower Glyphosate
Linuron
Metalochlor
Groundnut
0.10
Banana
0.20
Tea dried
0.10
Carrot
1.00
Cotton seed
0.25
Sorghum grain
0.25
Sorghum fodder
1.00
Soybean
1.00
Groundnut
0.10
Sorghum grain
0.30
250
Sorghum fodder
2.00
Soybean and cotton
0.10
seed Metribuzin
Corn
0.25
Potato
0.60
Soybean,
sugarcane
0.10
and tomato
0.75
Wheat grain
1.00
Wheat straw Molinate
Rice grain and straw
0.10
Oxidiazon
Groundnut
0.50
Rice grain
0.05
Rice straw
0.20
Banana, cotton seed,
0.05
Oxyfluorfen
soybean,
vegetables
and fruit crops Paraquat
Sugarcane and cotton
0.50
seed
0.05
Banana,
vegetables
and sorghum Pendimethalin
Sorghum, groundnut, cotton seeds, corn, beans an onion
0.10
Rice grain
0.05
251
Simazine
Thiobencarb
What grain and straw
0.10
Banana
0.20
Corn and sugarcane
0.25
Rice grain
0.25
Rice straw
1.00
Trifluralin 2, 4- Barley, corn, cotton seed, D
groundnut and wheat
0.05
Barley grain
0.50
Barley forage
20.0
Corn grain
0.50
Corn, fodder and forage
20.0
Corn
seed,
fruit
and
0.10
vegetables
0.10
Rice
20.0
Rice straw
0.50
Sorghum
20.0
Sorghum fodder
2.00
Sugarcane
2.00
Wheat grain
20.0
Wheat straw Source: The Pesticide Chemical News guides 1985 by Food Chemical News.
252
APPENDIX-VII List of Herbicides by common name, trade name, manufacturer, time of application and rate of application Commo Trade n name
Alachlor
Amitrle
name
Lasso
Weedaz
Molec Manuf Time of ular
acture
applicati
(kg
wt.
r
on
ha-1)
Monsan
Pre, ppi,
to
early post
Amche
Pot
2-8
Ciba-
Pre, ppi,
1-3
Geigy
early post
Kumiai
Pre, early
chem.
pot
269.8
84.1
l Atrazine
Aatrex,
Rate
1-3
m 215.7
Gesapri m Benthioca
Bolero,
rb
Saturn
257.8
253
2-4
Bromacl
Hyvar-
261.1
Du Pont
Pre
1-5
311.9
Monsan
Pre, post
1-3
Pre
2-4
X, KrovarL Butachlor
Machet e;Delchl
to;
or
Coroma ndel Indag
Chloramb
Amibe,
en
Vegibe
206.0
Amche
Cycloate
Ro-Neet
215.4
Stauffer
Ppi
2-5
Cyprazine Outfox,
227.7
Gulf
Post, pre
0.5-
m
Prefox
2.0
254
Dalapon
Dowpo
114.3
Dow
Post
2-5
221.0
Velsicl
Post pre
0.5-
n Dicamba
Banvel
2.0 Diquat
Reglone
184.0
ICI
Post
1-4
Diuron
Karmex
233.1
Du Pont
Pre, early
0.5-
post
3.0
Du Pont
Pre
2-6
Ciba-
Pre, post
0.5-
Fenuron
Dybar
164.2
Fluoment
Cotoran
232.2
uron
; Lanex
Geigy;
2.0
Amche m Fluorodif
Prefora
Ciba-
Pre, early
en
n;
328.2
Geigy;
pot
Soyex
Nor-Am
255
2-4
Glyphosat Roundu e
p
Hexaflura
Nopalm
te
ate
Isoproturo Arelon; n
Linuron
169.1
228.0
Monsan
0.5-
to
2.0
Pennwal Post
2-4
t Dow -
Hoechst
Tolkan;
; May
Gramiro
and
n
Baker
Afalon,
Post
249.1
Post
0.51.5
Du Pont
Pre, post
2-4
Chipma
Post
0.25
Post
0.5
Lorox MCPA
Ca-
2.0
Trol;
200.6
n; Dow
Thistrol MCPB
Ca-
288.5
Chipma
1.5
Trol;
n;Amch
Thistrol
em
256
Methaben
Tribunil
221.3
Bayer
Pre, post
1-3
1-2
zthiazuro n Metolachl
-
-
Monsan
Pre, early
to
pot
-
Sandoz
Post, pre
1
214.3
Boyer
Pre, early
0.5-
post
2.0
Post
2.5-
or Metoxuro
Dosane
n
x
Metribuzi
Sencor
n MH
MH-30;
112.1
Retard
Uniroya l; Ansul
5.0
Monurn
Telvar
198.6
Du Pont
Pre
2-4
MSMA
Ansar-
162.0
Ansul
Post
0.25-
529
2.0
257
Neptalam
Niralin
Alanap,
291.3
Uniroya
Peach
l,
Thin-
Amche
322
m
Planevi
345.1
Shell
Pre
4.0
Ppi, pre
n Nitrofen
TOK
2.0-
0.51.5
284.1
Rohm
Pre, early
2.0-
& Hass
post
4.0
Pre, post
0.2-
(Indofil) Oxyfluorf
Goal
-
en
Rohm & Hass
1.0
(Indofil) Paraquat
Gramox
186.2
ICI,
one,
ACCI,
Ortho
Chevron
258
Post
0.20.5
Pendimet
Prowl,
halin
Herbad
-
Cynami
Pre, ppi
de
1.02.0
ox, Stomp Picloram
Tordon
241.5
Dow
Post
1.02.0
Propanil
Stam F-
218.0
Indofil
Post
34 Propazine
Milogar
2.05.0
229.7
d,
Ciba-
Ppi, pre,
Geigy
post
Ciba-
Pre
Gesamil Semazine
Princep, Gesatop
201.7
Geigy
, Printop
259
1.03.0
Triallate
Avadex
304.7
BW,
Monsan
Pre, ppi
to
Far-Go Trifluralin Traflan
335.3
Stauffer
Pre, ppi
0.51.5
2,4-D
2,4-D
221.0
Many
Pot
compani
0.51.5
es 2,4-DEP
Falone,
649.1
Falodin Vernolate
Vernam
Uniroya
Pre
l 203.4
Stauffer
1.04.0
Ppi, pre
2.04.0
Ppi = Pre-plan incorporation; Pre = pre-emergence; Post = post-emergence (Note: Rate of application depends on the crop grown, weed species present and soil type)
260
APPENDIX-VIII Abbreviations used in weed management Abbreviation
Full name
A
Annual
a.e.
Acid equivalent
a.i
Active ingredient
BLW
Broad leaf weed
CDA
Controlled droplet application
CFS
Cubic foot per second
Cm
Centimeter
Cu
Cubic
DCA
Direct contact application
Ec
Emulsifiable concentrates
GR
Granules
GPM
Gallon per minute
ha
Hectare
P
Perennial
PPM
Parts per million
PPMV
Parts per million by volume
PPMW
Parts per million b weight
Post Em.
Post-emergence
261
PSI
Pound per square inch
Pre.Em
Pre-emergence
Ppi
Pre plant incorporation
Pp
Pre planting
Sc.
Solution concentrate
SP
Soluble powder
Sp. Gr.
Specific gravity
Sq.
Square
V/v
Portion by volume
WP
Wettable powder
WSC
Water Soluble concentrate
W/V
Portion by Wright per unit volume
W/W
Portion by wright
262
GLOSSARY OF WEED CONTROL TERMINOLOGY Arboricide:
A chemical used to killing tress or woody shrubs.
Absorption:
The process by which herbicides are taken into plants by roots or foliage (stomata, cuticle etc.)
Active
The active toxic materials present in a
ingredient:
formulation.
Adjuvant:
A substance added to prescription to aid in the operation of the main ingredient. Purpose of adding adjutants to pesticides: improve wetting,
reduce
evaporation,
improve
deposition, increase penetration, improve translocation, extend weather ability, slow release,
pH
adjustment,
increase
compatibility, reduce drift, and minimize or inhibit odour. Amine:
A liquid concentrate form of 2, 4-0 or MCPA When mixed in water amine formulation forms a uniform solution. They are never
263
mixed in oil. They have practically no volatility and therefore are considered safer to use near susceptible plants. Analog:
A compound that is very similar in both structure and formula to another one.
Alien weed:
Weed not native of a country. Associated weed: Non-parasite weed association with a specific crop.
Allelopathy:
Any direct or in direct harmful effect by one plant on another through production of chemical
compound
on
antagonistic
interaction of phyto chemicals on the growth another plants. Activeingredi Is the part of formulated product mainly ent(ai):
responsible for herbicidal effects.
Band or row Treating the narrow strip in, on or along the application:
crop rows. The space between rows is not chemically treated. This method reduces chemical cost. The treated band is often onethird of the total area with comparable saving of chemical cost. In addition, where chemical. has a long period of residual soil toxicity, the
264
smaller total quantity of the chemical reduces residual danger to the succeeding crop. Basal
Herbicidal treatment applied to the stem of
treatment:
woody plants just above the ground line.
Blanket broadcast:
or An application over an entire area or field rather
than
only
on
rows, beds, and
application middles or individual plants. Broad leave In general, opposed to grass-lid plants. plants: Bio-
Pathogens such as bacteria, fungi and virus
herbicides:
when weed as bio-control agents.
Basophilic:
Weeds that can grow will in alkali soils.
Carrier:
The liquid or solid material added to a chemical or formulation to facilitate its preparation, storage, shipment, or use in the field.
Contact
A herbicide that kills primarily by contact
herbicide:
with plant rather than as a result of translocation.
Control:
The process of limiting or reducing pest population below an economic level by any
265
control measure: Calibration:
The process of finding out the exact quantity of carrier (water) required for spraying unit area:
Compatible
are used to intimately mix :fertilizer and
agent:
pesticide in spray liquids.
Chemical
is the effectiveness of active ingredient in the
stability:
formulated product.
Concentrated are prepared by dispersing an aqueous :
solution of herbicide in a water miscible
Emulsion
solvent by means of a colloidal mill.
Defoliant:
A chemical, which causes the leaf, or foliage, to drop from the plant.
Desiccant:
A chemical, which promotes the dehydration of plant tissues.
Detergent:
A chemical having the ability to remove oil. These may be used as surfactants in herbicidal sprays, which remove waxy substance, found on many of the weed leaves.
Direct
An application to a restricted area, such as
266
application:
row or bed at the base of the plants.
Dispersants:
Chemical that keeps the fine particles of Wettable powder in suspension.
Deposit
are chemicals added to herbicide concentrates
builders:
to keep the toxicant in intimate contact with plant surface.
Ecology:
Is the stud; of the reciprocal relations between organisms and their environment.
Emergence:
The time when the first leaves of the crop plant come through the ground.
Emulsion
The suspension of one liquid as minute globules in another liquid for example, oil dispersed in water.
Emulsion
A liquid formulation of a concentrated
concentrate
pesticide, which is diluted with water or oil to form an emulsion.
Epinasty:
Increase concentrate or granular form of 2, 4-D or 2, 4-T acid. The liquid forms are miscible in oil and form emulsions when diluted with water. They may be either regular or of low volatility and
267
usually give faster kills to susceptible plants. Emulsifiers:
Are the substances cause an emulsion concentrate to disperse spontaneously in to small stable droplets when added to water.
Emulsifiable
Emulsifiable concentrates upon dilution
concentrates
with water give stable emulsion suitable
(EC)
for spraying plant surface, emulsion at equal concentration of active ingredient are
usually
more
effective
than
corresponding suspension. Formulation:
The way in which basic pesticide chemicals are prepared for practical use. Includes
preparation
powders,
granules,
as
Wettable emulsifiable
concentrates etc. Flame
When annual broad leave seeds and
cultivation:
grasses in widely spaced crop rows are burnt the process is called flame cultivation.
Fumigants:
Are volatile chemicals applied in to
268
confined space on in to soil to produce gas that will destroy weed seed and act as soil sterilant Facultative
Weed
of
wild
community
origin,
seed:
escaping sometimes to cropland.
Granules (G):
pesticide formulation in which the active. ingredient is impregnated on small particles of clay, sand etc.
Growth
An organic substance effective in minute
regulator:
amounts for controlling or modifying plants processes.
Granules (GR): Granule
contains
1-20
percent
concentration of herbicide in a particular solid carrier suitable for direct field application. Herbicide:
A Chemical used for killing or inhibiting the growth of plants.
High volume:
Spray application of more than 750 litres per hectare.
Humicants:
Are chemicals that prevent rapid drying
269
of herbicide sprays on foliage. Herbigation:
The application of herbicide with irrigation water.
Herbicide
Use of two or more selected herbicide
rotation:
for crop situation and these are used in alternate years in sequence.
Herbicide
Use of more than on herbicide in a crop
combination
situation in a particular season or time Herbicide:
Integrated
is the weed population management
weed:
system that uses all suitable techniques
Management
in a compatible manner to reduce weed population and maintain them at level bellow those causing economic injury.
Low volume:
Spray application of 60-250 litres per hectare.
Miscible
Two or more liquids which when
liquids:
combined together, form a uniform a uniform stable mixture under normal conditions.
Miscible oil:
It consists of herbicide, solvent and
270
emulsifier. Noxious weed:
An
undesirable
troublesome
seed
difficult to control. Neutrophiles:
Weed growing well in neutral soils.
Non-selective
Refers
herbicide:
vegetation.
Noxious weed:
to
herbicide
used
to
kill
all
A plant arbitrarily defined by law as being specially
undesirable,
troublesome
and
difficult to control. Oil solution:
Chemicals in oil solution, which are, ready to use or need to be diluted further in oil.
Parts per million:
The number of parts by weigh or volume of a given compound in one million parts of final mixture
Pest:
A collective forms for organisms such as insects, disease pathogens, nematodes, weeds, rodents, bird etc. that are detrimental or annoying to man at a given time and place
Pesticide:
Any substance or mixture of substances intended for controlling insects, rodents,
271
fungi, weeds and other forms or animal life considered to be pests. Post-emergence
Treatment made after crop or weed plants
Treatment:
have emerged above the soil surface.
Pre-emergence:
Treatment made after crop is planted but
Treatment:
before it immerges. The pre emergence treatment may be contact or residual in action
Protected spray:
When application of nonselective herbicide is done to obtain the selective weed control in distantly planted crops by covering non target plants, if the soil conditions do not permit manual or mechanical weeding.
Selective
Refers to a herbicide that is more toxic to one
herbicide:
plant than to another. When such a herbicide is applied to mixture or plants some may be killed and others may be affected only slightly or not at all.
Smothering
Are those, which through their chick canopy
crops:
exclude, light and prevent all top growth of weeds.
Soil application:
Application of chemical made primarily to
272
the soil surface rather than to vegetation Spray drift:
The movement of airborne sprays particles. The amount of spray drift depends upon the size of the droplets, amount of wind and the height above the ground that the spray is released.
Suspension:
A system consisting of finely divided solid particles dispersed in a solid, liquid or gas.
Soil injection:
Mechanical placement of the herbicide beneath the soil surface with a minimum of mixing or stirring.
Spreading agent:
A substance used to improve the wetting, spreading or possibly the adhesive properties of a herbicide spray solution.
Soluble
power SP is similar to Wettable powder except that
(SP):
the technical gradients as well as dilutes. The formulating adjuvant used is completely dissolved in water or another liquid.
Satellite seed:
A weed that has become an integral part of ecosystem.
Safener:
Are substances used along with herbicides to
273
product crop. Selectivity:
Is the phenomenon where in a chemical kills the target plant species in a mixed plant population without harming the other plants.
Spot treatment:
When the herbicide is applied to small patches of weeds leaving the relatively weed free patches untreated.
Surfactants:
Are the material which favour or improves the
emulsifying,
wetting
or
dispersing,
spreading,
surface
modifying
other
properties of herbicide formulation. Stabilizers:
Are the chemicals used for obtaining stable emulsion and suspension in the spray tank individually.
Systemic
A herbicide that is translocated within the
herbicide:
plants.
Translocated
A herbicide, which is moved within the
herbicide:
plant from the point of entry.
Total weed
That form of weed controls which involves
control:
killing all plant cover. Also known as Nonselective weed control.
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Toxic:
Is another name for "poisoning power" Some chemicals has a high toxicity and some have a low toxicity.
Tolerance
Tolerance-pesticide:
The
amount
of
pesticide:
pesticide chemical allowed by law to be in or on the plant or animal product sold for human consumption.
Weed:
A plant that grows where it is not wanted.
Weed control:
The process of limiting weed infestations so that crops can be grown profitably or other operation can be conducted efficiently.
Weed ecology:
Concerns with growth characteristics and adaptations or survival mechanisms that enable
weeds
to
persist
in
those
environments altered by man for his use. Weed competition May be defined as the reduction in crop index:
yield due to presence of weeds in comparison to weed-free plot.
Weed prevention:
Process of stopping weeds species from entering,
spreading,
or
increasing
population in an area or field.
275
in
Wetting agent:
A compound which when added to spray solution causes it to spread over and wet plant surfaces more thoroughly.
Weed eradication:
Infers that a given weed species its seed and vegetative parts has been killed on completely removed from a given area and that the weed will not reappear unless reintroduction to the area.
Weed control
Can be worked out from reduction in the
efficiency
weed population due to weed control method over un-weeded check.
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