The Effect of Grazing and Clipping on the Control of ...

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carrot (Daucus carota L.) was redtuced, but on pastutres tinder heavy grazing, cattle prevented regrowth and seed production of flowering plants. To simulate theĀ ...

Weed Science Society of America

The Effect of Grazing and Clipping on the Control of Wild Carrot Author(s): P. J. Harrison and H. M. Dale Source: Weeds, Vol. 14, No. 4 (Oct., 1966), pp. 285-288 Published by: Weed Science Society of America and Allen Press Stable URL: . Accessed: 25/06/2014 16:26 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .

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G. C., R. C. SCHRAMMt,JR., ani(1H. CARDENNAS. 1961. Applying EPTC with emphasis on method of soil incorporationI. Proc. SWC 14:63-68. 17. LINDER, P. F., W. C. SHAW, and P. C. MARTH. 1955. A com-

(linitro-ortho-secon(lary Iult)yl phenol. Proc. NEWCC 8:21-22. 19. MEGGITT, W. F., R. J. ALDRICH, and J. C. CAMPBELL. 1958. An evaluLation of spray and granular applications of herbicides for weed control in potatoes after the final cultivation. Proc. NEWCC 12:66-70. 20. WIESE,A. F. and R. S. DUNHANM. 1954. The period of toxicity of IPC andl CIPC when applied to the soil at variotis times of the year. Res. Rept. NCWVCC11:46.


parison of the relative vapor activity and the relative rates of evaporation of several carbamates. Proc. SWC 8:306-308. 18. M[EG(GITT, W. F., H. A. BORTHWICK,R. J. ALDRICH, and W. C. SIIAW. 1954. Factors affecting the herbicidal action of

The Effect of Grazing and Clipping on the Control of Wild Carrot' P. 1. HARRISON and H. M. DALE2 plants in a stand are heterogeneous in age, as in wild carrot, then control by herbicides is inefficient. Wild carrot propagates solely by seed which may lie dormant but viable for at least seven years in the soil (16), thus acting as a reserve for the population of this plant. Dale et al. (4) have shown it to be a plant that occurs at an early successional stage in abandoned fields and pastures. It is an abundant species in infrequently mown hay fields but also occurs in under-utilized pastures in much of the rough land of Ontario and Quebec. In these rough areas, mowing or grazing of the plants at a time when seed production will be curtailed should reduce the wild carrot population in favor of plants which are more beneficial as fodder. The purpose of this study was to determine the effect of clipping and grazing patterns on the ultimate seed production on three different soils, and to determine the most nutritive stage at which wild carrot might be cut or grazed. These studies will have direct bearing on the control of this weed by cutting and grazing, and may indirectly suggest the age at which a damaging herbicide should be most effective in reducing seed production.

Abstract. Under light grazing, the reproductive capacity of wil(d carrot (Daucus carota L.) was redtuced, but on pastutres tinder heavy grazing, cattle prevented regrowth and seed production of flowering plants. To simulate the effects of cattle grazing, seedlings and flowering plants were clipped at different times during the summer on natural and experimental plots on different soil textures. Plants on fine texttured soils were larger in size, regenerated more rapidly, and had a higher survival rate after clipping. The most efficient time for control by a clipping treatment, determined on the basis of prevention of seed production and mortality of plants, was in the latter part of AuLgLust. INTRODUCTION

ATILD carrot (Daucus carota L.) plants of the same age

IV and morphology are not equally susceptible to control with 2,4-dichlorophenoxyacetic acid (2,4-D). Switzer (17) reported the existence of a strain of wild carrot resistant to 2,4-D. Whitehead and Switzer (18) studied the differential response of resistant and non-resistant strains to 2,4-D and related herbicides, and found that the resistance developed between germination and the cotyledon stage. Switzer3 suggested that plants grown from seed collected from plants at the edge of the road are less responsive to 2,4-D treatment than those grown from seed collected in pastures where the wild carrot population is not subject to periodic spraying with a herbicide. Dale and Harrison (3) studied the germination pattern in wild carrot and found several flushes of germination throughout the growing season (related to the occurrence of a soil-soaking rain following the removal of a mechanical dormancy). Hoffman et al.4 have demonstrated that the age of the plant is critical in the control of wild oat (Avena fatntaL.) by 4-chloro-2-butynyl N-(3-chlorophenyl) carbonate. In stands of weeds of uniform age, the most efficient use of a herbicide can be made by application when the plants are at the most susceptible age. But when



All studies were conducted in Wellington County in Ontario. Six discrete areas, 4 miles northeast of the town of Arthur, gave two replicates each on Toledo clay loam and muck, and one each on Donnybrook sandy loam and Granby sandy loam. These were ungrazed pastures, abandoned for over 10 years, and recently planted in widlelyspaced conifers. Monthly averages for temperature and precipitation were recorded. Soil samples were analyzed for inorganic nutrients, field capacity, permanent wilting point, percentage organic matter, texture, and percentage water available to plants. Soil temperatures and drainage were recorded. Seed plots. Within each of the above six areas, a 50 sq m (10 m by 5 m) tract was selected, dug to a depth of 15 cm, and then enclosed with barbed wire to prevent disturbance. Sixty plots, 60 by 45 cm, were subjected to 15 treatments randomly arranged and replicated four times in each 50 sq m tract. Seed was sown May 8, 11, and 18 on muck, sandy, and clay loam, respectively, at densities of 50, 150, and 300 mg of seed per plot, and covered with

1Received for publication September 30, 1965. Contribuition (incorporating part of a Master of Science thesis) from the Department of Botany, Ontario Agriculttural College, University of Gutelph, Guelph, Ontario, Canada. 2Gradtiate student and Associate Professor. Student's present address: Mfantsiman School, Box 14, Saltpond, Ghana, West Africa. 3Personal Communication. 4Hoffman, 0. L., J. W Pullen, J. R. Epperly and T. R. Hopkins. 1959. Factors affecting the activity of 4-chloro-2-buttynyl N-(3chorophenyl) carbonate as a selective herbicide. Spencer Chemical Co. Mimeo.


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soil. Plots in which no seed was planted were used to measure the number of volunteers from seed previously in the soil Five clipping treatments included clipped twice (July 23 and August 25), clipped once July 23, August 27, September 15, and an unclipped control. The time of seedling emergence and the number of wild carrot plants present at the time of each clipping treatment were recordle(l.Plants were clipped 3 cm above the crown of the root. Seedling leaves lying flat on the ground were gathered up an(dcut. Clippings were oven-dried and weighed. In October, only plants within the center 40 cm sq of each plot were harvested an(danalyzed. Transplant plots. Within each of the six 50 sq m barbed wire enclosures, 45 plots each 45 sq cm in size were transplanted to wild carrot rosettes of uniform size at (lensities of 2, 6, and 12 plants per plot. Mluck,sandy, and clay loam plots were planted May 12, 15, and 19, respectively. Plants that died within the first week were replaced and one week later the number of plants in each plot was recorle(l. The plants were subjected to one of five clipping treatments: clipped twice June 23 and August 27, or once June 23, July 25, or August 27, or the unclipped control. The plants were clipped just above the first green leaf to ensure that similar amounts of photosynthetic material remaine(1 after cutting. Clippings were oven-dried and weighedl. In October, flowering plants were harvested and each plant was analyzed for height, number of mature compoun(I umbels, number of immature compound umbels, (lried root weight, dried shoot weight, length of root, number of root branches and survival. Seed collected from these plants was stored at room temperature in paper bags and germinated the following spring in petri dishes. Greenhouse experiments using samples of the same three soils, similar densities, and clipping treatments were used to confirm some of the data. Natural plots. No wild carrot plants were found in the muck areas, but five permanent quadrats, each 1 m sq in size, were set up on each of four undisturbed pasture sites of sandy and clay loam. Plots were treated in one of four ways: clipped once June 23 or July 28, three times June 23, July 28, and August 29, or unclipped controls. All plants including seedlings were clipped 3 cm above the crown of the root. Clippings of wild carrot plants were collected, oven-dried, and weighed. Flowering plants that survived the treatments were collected October 10 and analyzed for growth (dried weight of root and shoot, height, number of compound umbels immature or with seed, and survival) and reproductive capacity. The percent germination of seed produced by plants surviving the clippings was tested as described previously (3) Pastuzre plots. Six pastures in the Guelph area were classified into zero, light, and heavy grazing intensities depending on the density of cattle. All the pastures were of similar vegetational composition andl soil characteristics. On August 12, 100 flowering plants of wild carrot were collected from each pasture and the plants sorted arbitrarily into four categories on the basis of the amount of plant consumed. In each pasture, the number of seedlings and flowering plants was counted in 40 cm squares at 1 m intervals


along a transect. Five hundred seeds from plants under each grazing intensity were stored in paper bags at roomn temperature and germinated the following spring. Germination tests were made as described (3). Flowering plants were analyzed for amount consumed, height, shoot weight, root weight, root length, root diameter, number of compound umbels, stage of flowering, distance between plants, and reproductive capacity. NTttritive tests. Digestibility and nutritional tests were carried out on the fall foliage of seedlings and on flowering plants grown in the greenhouse. An artificial rumen was used in the former case. RESULTS

In the analysis of the sites, there were no marked differences in nutrients, pH, amount of water available to plants, and soil temperature. However, the percent organic matter, drainage, and texture varied among the plots. Organic matter increased from sandy loam to muck. Drainage increased from clay loam to sandy loam to muck. Seed plots. The first seedlings appeared 20, 23, and 27 days after planting on the muck, sandy, and clay loam soils, respectively. Only one or two volunteer seedlings emerged from seed previously in the soil on the clay and sandy loam control plots; no volunteer seedlings were present on the muck control plots. A large population of seedlings on the muck became established quickly and the number remained constant over the summer. In contrast, the populations on sandy and clay loam soils were small in June but increased 50 to 100%oas a result of summer germination following heavy rains. On clay loam, seedlings were still emerging in October. At harvest time, the size of the populations increased progressively from sandy loam to clay loam to muck. Approximately 5%Oof all plants on muck, clay, and sandy loam plots had initiated flower buds by July 23, 25, and August 6, respectively. The percentage of these annuals was constant regardless of clipping treatment or soil type. Seed did not mature from these flowers. Plants regenerated very little after clipping and died after flowering. A comparison was made of the length, diameter, and weight of roots, the number of branch roots, and the average weight of clippings for seedlings from the different soils. Seedlings from clay loam were significantly larger, followed by seedlings from muck and sandy loam in that order. Mean values throughout the study were tested using Duncan's Multiple Range test. Plants clipped twice during the summer were the smallest. Plants clipped once in September, August, or July were smaller than control plants but not significantly (lifferent from each other nor was the weight of clippe(d herbage. Transplant plots. Flowering plants from muck and sandy loam plots were of similar size and seed-producing ability, while on clay loam they were taller, with larger roots an(d shoots, and produced more umbels. On clay loam, more flowers, regrowth, and a higher survival rate occurred than on the other soils or the controls. Density of planting had no apparent effect on the size of plants. Plants subjected to the double clippings were in bud


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in June and early bloom in August. They showed little recovery, produced no viable seed, and had the highest mortality rate. When plots were clipped once in june when the plants were in bud, some plants recovered and grew to three-quarters of the control height, floweredl again, and produced almost as many seed umbels as the control plants. Root and shoot weights were only slightly less, but the survival rate was significantly less than the control. Plants clipped once in July when in full bloom, flowered again but produced no viable seed. Clipping once in August in the green fruit stage resulted in only slight regrowth and the production of few flowers and no viable seed. The single clipping in June was the only treatment which allowed subsequent seed production. These plants produced immature seed on all three soils. Using seed production and survival rate as criteria to measure the effectiveness of the different clipping treatments, clipping once in July or August, or twice in the summer, were of value; clipping once in June was less effective as a control measure than the other treatments. Clipped natural plots. Plants clipped three times when in bud, full bloom, an(d bud, respectively, produced little leaf growth an(d no mature seed, and had the lowest survival rate of any treatment. WAlhenplots were clipped once in June when the rosettes were in the bud stage, the plants regrew to one-half the height of control plants, flowered again, produced fewer viable seeds, and showed a significantly higher mortality. Clipping once in july in the green seed stage resulted in plants regenerating to one-quarter the control height. Flowering plants produced no mature seed. The population of all wild carrot plants clipped in July had a lower survival rate than those clipped once in June. The production of foliage was not stimulate(d by any of the clipping treatments. Using the criteria of high mortality and low reproductive capacity, clipping three times, and clipping once in July, were the most effective. Clipping once in June was not significantly effective on any plot. After cutting, generally, plants on clay loam recovered more quickly, regenerated to a greater height, and had a higher survival rate than those plants on sandy loam. Pasture plots. Flowering plants in early bud to full bloom were grazed with other pasture plants by cattle, but plants in late flowering stages were avoided. As grazing intensity increased, the number of plants and amount of each plant grazed increased. Pastures under light grazing contained plants primarily ungrazed or with only the terminal flower stalk grazed. In the latter case, this resulted in a larger number of flowers, a less advanced stage of flowering, and lower shoot height; root development was normal. All the plants on heavily grazed pastures had several or all flower stalks grazed. These plants were severely retarded in flowering and reduced in shoot height, but similar to those under light grazing in the number of flowers per plant and in the size of the root. The dlensity of seedlings and flowering plants and the percent germination of see(ds decreasedl as the grazing intenisity increase(l The average niumber of seed-producing compound umbels per plant was 4.0, 3.0, an(d 0.1 for zero, light, and heavy grazing, respectively. The prostrate form of see(dlings and rosettes makes

their grazing difficult for cattle, but the subsequent development of an upright flower shoot allows large amounts of herbage to be removed easily. Presumably, root development is almost complete at this time as differences in root weight, length, and diameter were insignificant between clipped flowering plants and seedlings. Under light grazing, the removal of the first or second order umbels did not retard flowering enough to stop seed production from higher order umbels, but seed viability was reduced. Any seeds produced under heavy grazing remained green and unripe since the regrowth was kept grazed. On heavily grazed pastures, the plant population could only be maintained by seed previously in the soil or by seed from a surrounding area. Nutritive tests. The seedling foliage had a digestibility of 72%; it contained 14% protein, 1.8%ocalcium, 0.24C/c phosphorus, 16%ofiber, and 13.6% total ash. Analysis of the flowering plant foliage gave similar results. The digestibility and nutritive values of wild carrot are high, similar to legumes, but much higher than the values for grasses. However, it has been suggested (10, 14) that the cattle may avoid the plant due to its low palatability. DISCUSSION

Severe frost heaving occurred in muck and wet clay areas during the early spring, limiting natural populations by disturbing the top layer of soil. This may account for the absence of wild carrot in the natural vegetation on muck soils. However, the largest population of wild carrot seedlings became establishecd on muck in experimental plots. Fine textured soils provide the most suitable conditions for flowering plants of wild carrot during periods of stress such as partial defoliation. Control treatments should be more successful in reducing populations on coarse soils, where wild carrot has difficulty surviving under stress. The high nutritive and digestibility ratings found for wild carrot agree with the estimates of Ellenberg (7) and Klapp (12). The latter has stated that such weeds of high food value should be regarded with greater tolerance when they are found among plants of low value. Fairbairn and Thomas (8) have discussed the potential nutritive value of 20 common weed species. Several, including ribgrass (Plantago lanceolata L.), bulbous buttercup (Ranunculus bulbosus L.), and dandelion (Taraxacum officina'le Weber), have high nutritive value which would make their herbage of value under some circumstances. However, Georgia (10) and Spencer (15) have claimed that cattle tend to avoid wild carrot because of the acrid juices in its leaves, and Mluenscher (14) demonstrated that milk of dairy cattle may be tainted by grazing large amounts of this weed. Clark and Fletcher (2) reported that sheep will suppress it in pastures. In Europe, wild carrot occurs more frequently in meadows than in pastures (6, 12). The conclusion is that low infestations of wild carrot can be suppressed by grazing pressure before the flowering stalks become unpalatable. Studies on alfalfa by Grand(lfiel(d( 11) suggeste(l that relating the time of cutting to the time of minimum food reserve may aid in solving the problem of controlling weeds in native pastures. When wild carrot seedlings were


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clipped, foliar regrowth occurred, presumably at the expense of the root reserves as indicated by a smaller root size. A single clipping at different times produced no effect on the root size at the end of the first growing season. Only when the plants are clipped more than once is the root affected. Neither time nor frequency of clipping, per se, affects the mortality of first-yearplants. Muenscher (13) observed that after hay was cut, the second growth contained more wild carrot plants than grass or clover. As a means of control, he has suggested mowing a second time when flowers are immature prior to seed set. However, the control by cutting flowering plants of wild carrot in bud to full bloom (the suggested times of minimum root reserves in other plants and the efficient time for control purposes (1, 5, 11)) resulted in the revival of axillary buds giving rise to more flowers and production of some viable seed. Dale and Harrison (3) have shown that seeds germinate in several flushes during the growing season so that volunteer stands are nonuniform in age. Control should be aimed at the prevention of seed production in this noxious weed which reproduces solely by this method (9). Cutting in August (in the latitude where these experiments were carried out) when the seeds are immature is the most efficient. The shortened growing season remaining prevents the proluction of viable seed even though root reserves might be adequate. No flowering plants have been found to overwinter. ACKNOWLEDGEMENT

The authors wish to express their gratitude to Dr. D. N. Mowat, Department of Crop Science, University of Guelph, for his assistance in the determination of digestibility using an artificial rumen. The analyses at the Nutrition Department, University of Guelph, under the direction of Professor D. Arthur, are gratefully acknowledged.


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