TDOC Z TA245.7 B873 NO.1540 lg 2Q E TEXAS AGRICULTURAL EXPERIMENT STATION / Neville P. Clarke, Director The Texas A&M University System / College Station, Texas 1986 EFFECT OF PICLORAM AND TEBUTHIURON ON BROADLEAF WEEDS AND BERMUDAGRASS IN EAST—CENTRAL TEXAS PASTURES' $5 ,,,n»- AUTHORS R. W. Bovey, research agronomist, Agricultural Research Service, U.S. Department of Agriculture and The Texas Agricultural Experiment Station (Department of Range Science), College Station, Texas; Headquartered at the Grassland, Soil and water Research Laboratory, USDA-ARS, Temple, Texas R. E. Meyer, plant physiologist, Agricultural Research Service, U.S. Department of Agriculture and The Texas Agricultural Experiment Station (Department of Range Science), College Station, Texas; Headquartered at the Grassland, Soil and water Research Laboratory, USDA-ARS, Temple, Texas J. R. Baur, plant physiologist (deceased), Agricultural Research Service, U.S. Deparment of Agriculture and The Texas Agricultural Experiment Station (Department of Range Science), College Station, Texas" b5. V. Schulte, formerly biological technician, Agricultural Research Service, U.S. Department of Agriculture and The Texas Agricultural Experiment Station (Department of Range Science), College Station, Texas 2 CONTENTS SUMMARYQ00000000000000000000000000000000ooooooooooooooooooocooooooooooooooooo INTRODUCTIGNIOOOOOOQOOOOOOQCOCOOOCOCOCOOIOOOOOOIIOOOOOOOOOOOOOOOOOIOOOOOOOOOO MATERIALS AND METHODSQQQQQ000000coooaoooooooooooooooooooo00000000000000000000 Experimental Sites......................................................... Experimental Design........................................................ Evaluation and Statistical Analysis........................................ RESULTS AND DISCUSSION...........................................,........... Effect of Single Application on weed and Grass Cover....................... Effect of Double Application on weed and Grass Cover....................... Results of All Treatments on weed Population............................... kO@UlO\U1U‘l-l>-Pbdl\) SUMMARY Pellet and spray formulations of picloram and tebuthiuron were applied side-by-side at rates of 0.37, 1.12, and 2.24 kg/ha to common bermudagrass (Cynodon dactylon (L.) Pers.) growing on a heavy clay site and a sandy site. Six replicate plots were treated at 6-week intervals between October 1974 and September 1975. Six months after the original treatment, half of the replicate plots were retreated with the same herbicides. A single application of most herbicides reduced weed cover on the sandy site for 1 year, but weed control was less than 1 year on the clay site. Results for double herbicide application were similar to single application, except that little residual herbicide activity was apparent on either the sandy or clay site 1 year after retreatment. On the clay site, a single application of tebuthiuron spray in October 1974 at 2.24 kg/ha was the only treatment that resulted in significant increases in bermudagrass cover after 1 year. After 1 year on the sandy site, significant increases in bermudagrass cover occurred following single sprays of picloram at 2.24 kg/ha in November 1974 and March 1975 and tebuthiuron sprays of 1.12 kg/ha in March and May 1975. Picloram and tebuthiuron sprays at 2.24 kg/ha doubled bermudagrass cover when treated in January 1975 and retreated in July 1975 or treated in March 1975 and retreated in September 1976. Picloram pellets or sprays at 1.12 and 2.24 kg/ha applied in November 1974 and retreated in May 1975 also increased bermudagrass cover. Herbicide injury to bermudagrass on either the clay or sandy site was infrequent and temporary. Herbicide effectiveness on the clay site apparently was less than on the sandy site due to shorter term weed control and less response to increase in bermudagrass cover; - 3 Effect of Picloram and Tebuthiuron on Broadleaf weeds and Bermudagrass in East-Central Texas Pastures R. W. Bovey, R. E. Meyer, J. R. Baur, and S. V. Schulte INTRODUCTION Control of annual and perennial broadleaf weeds is a prerequisite for maxium grass production in established pastures. Use of herbicides is one of the most efficient ways to control weeds. In the past, the herbicide most frequently chosen for broadleaf weed control was 2,4,-D([2,4-dichlorophenoxy]acetic acid) (11). This herbicide is widely recommended for use in pasture and forage crops in Texas (20). Unfortunately 2,4-D lacks persistence (16), and its success depends on application at a time when the weeds are young and actively growing (20). Consequently, several applications may be required for effective weed control. As application and chemical costs increase, a more persistent herbicide may become economically feasible. In three of five experiments in central Texas, Mayeux (17) found that picloram was more effective as a spray than as pellets for control of pasture weeds. Tebuthiuron was more effective as a spray in one of two experiments, but none of the herbicides suppressed weeds during the second year after application. Kleingrass yields were increased by effective herbicide treatments during the growing season of application. In South Texas, Scifres and Mutz (21) found that forb production and diversity were decreased where 1 kg/ha or more tebuthiuron was applied but recovery of forbs was evident 3 years after treatment regardless of rate of application. The standing grass crops were significantly increased 1, 2, and 3 years after treatment. when applied during dry periods, picloram reduced density and yield of Coastal bermudagrass on a Lufkin sandy loam soil (5). Baur et al. (2) found that picloram at 2.2 kg/ha reduced common bermudagrass production when applied in March but not when applied in April or June on a Lufkin fine sandy loam. In the same study, common bermudagrass tolerated applications of tebuthiuron at 2.2 kg/ha in March and April but not in June. Picloram applied at 1.12 kg/ha to bare soil disappeared after 3 months but persisted for 6 months at 3.36 kg/ha in a lakeland sand (4). In a clay loam soil, picloram persisted at 0.03 ppm or less for 6 and 18 months from application of 1.12 and 3.36 kg/ha, respectively. Picloram was detected in the top 15 cm of the clay soil. Both experimental sites were near College Station, Texas. Merkle et al. (18) reported that picloram was more persistent in clay than in sandy soil because more picloram was removed by leaching from the sandy _ sites. Herr et al. (15) concluded that high organic content is essential to ‘ maintain phytotoxic levels of picloram in soils and that heavy and medium textured soils retained picloram near the soil surface, whereas the light- , 4 textured soils were easily penetrated to a depth of more than 61 cm. Grover (14) also correlated the soil activity of picloram with pH and organic matter but not with cation exchange capacity or percentage of clay. Bovey et al. (7) found that significant levels of tebuthiuron persisted in soil for 6 months after application of sprays or pellets at 2.2 kg/ha on a Bleiblerville clay (a member of the fine, montmorillonitic, thermic Udic Pellusterts) in a Coastal bermudagrass pasture. More tebuthiuron was present in the soil profile when the herbicide was applied as pellets than as sprays; however, the upper soil profile had the highest concentrations of tebuthiuron regardless of herbicide formulation. »Bovey et al. (8) also found that tebuthiuron persisted even for 2 years after treatment of pellets at 2.2 kg/ha on an Axtell fine sandy loam (a member of the fine, montmorillonitic, thermic family of Udertic Paleustalfs). Garcia and Gontarek (13) indicated that tebuthiuron was readily adsorbed and/or absorbed by organic matter in the upper‘ soil layer, retarding leaching to lower depths. Baur (1), however, showed that rate and extent of tebuthiuron leaching was inversely related to clay content of the soil. Chang and Stritzke (9) proposed that both organic matter and clay content were important because soil mobility of tebuthiuron was greatest in soil with low organic matter and low clay content. The importance of clay content in restricting tebuthiuron availability was shown by Fischer and Stritzke (12) in that the percentage of blackjack oak (Quercus marilandica Muench.) and post oak (Quereus stellata wangenh.) killed decreased asiElay content in the soil increased. This study examines the effectiveness of the herbicides picloram (4-amino-3, 5,6,-trichloro-2-pyridinecarboxylic acid) and tebuthiuron (N-[5-(1,1-dimethyl- ethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) on broadleaf weeds in bermudagrass pastures. These herbicides have persistence characteristics that have made them especially effective in controlling perennial woody vegetation (3,6,19). Primary objectives of this research were to evaluate the date of application of picloram and tebuthiuron with regard to changes in weed and bermudagrass cover. Other objectives were to examine the above parameters as influenced by type of formulation (aqueous spray versus pelleted herbicide), soil type, and effects of retreatment 6 months after the initial treatment. MATERIALS AND METHODS Experimental Sites Two sites for this study were chosen on the basis of soil type. A 0.8-ha bermudagrass pasture located in the woody Plant Nursery maintained by the USDA-ARS, Grassland Protection Research Unit at the Texas A&M University Research and Extension Center, Bryan, Texas, was selected for the heavy clay site (hereafter referred to as the clay site). The soil was a Wilson clay loam (a member of the fine, montmorillonitic, thermic Vertic Albaqualfs). At the onset of the study, the major grass species at this site was common 5 5 bermudagrass, with minor concentrations of brownseed paspalum (Paspalum licatulum Michx.), dallisgrass (Paspalum dilalatum Poir.), and johnsongrass (Sorghum halepense (L.) Pers.) plants. The second study site was in a 2.0-ha common bermudagrass pasture near Nellborn, Texas. The soil at this site (hereafter referred to as the sandy site) is classified as Lufkin fine sandy loam (a member of the fine, montmorillonitic, thermic Udertic Paleustalfs). The major grass species at the onset of the study was common bermudagrass, with scattered plants of brownseed paspalum and dallisgrass. ' The common and scientific names of the weeds generally distributed throughout the plots at both study sites are given in Table 1 (10). Experimental Design In September 1974, 294 plots (4.6 by 4.6 m each) were established at each site. Side-by-side comparisions of picloram and tebuthiuron were made by applying the same rate of each chemical in 1.5-m swaths to each plot. The sprays were applied with a tractor-mounted split-boom sprayer at 187 L/ha delivered at 210 kPa. Pellet formulations of both herbicides were broadcast by hand. The formulations examined were the potassium salt of picloram (240 g/L), 80% (ai) wettable powder of tebuthiuron, and 10% (ae or ai) pellet formulations of both herbicides. Extruded picloram and tebuthiuron pellets were 0.97 and 0.81 mm diameter, respectively. Beginning in October 1974 (Table 2), six replicate plots at each site were treated with 0.37, 1.12, and 2.24 kg/ha of both herbicides. The herbicides were applied every 6 weeks through September 1975. Approximately 6 months after the first treatments were made, three of the original six replicate plots were retreated with the same herbicide and rate as used for the first treatment. Dates of treatment, retreatment, and treatment evaluation, are given in Table 2. Six plots were maintained as untreated controls. Evaluation and Statistical Analysis Immediately preceding each application date and 60, 180, and 365 days after treatment, the entire treated areas (plots) were visually evaluated for percentages of weed cover and bermudagrass cover and the presence of specific weed species. The weed species evaluation, strictly a present or not present rating, was made for the purpose of assessing population shifts that occurred either as a result of seasonal changes or herbicide treatment. (or ange ). The individual cover ratings (weed and bermudagrass) for each treatment retreatment) were subjected to analysis of variance and Duncan's multiple-r test to determine the existence of differences resulting from treatment (22 6 RESULTS AND DISCUSSION Effect of Single Applications on weed and Grass Cover Clay Site Weed cover: Percentages of weed cover on the clay site 60, 180, and 365 days after treatment are presented in Tables 3, 5, and 6. Sixty days after treatment, most herbicides, except for the low rates (0.37 kg/ha) of pelleted picloram and tebuthiuron, effectively reduced the weed cover on the clay site (Table 3). Sprays of picloram and tebuthiuron applied in October, November, and January were generally more effective than pellets of the same herbicides. Sufficient rainfall was received from October 1974 through January 1975 to activate the pelleted herbicides (Table 4). Treatments applied in May, July, August, and September showed few differences between herbicide sprays and pellets, possibly because weed cover was greatly reduced in summer. Picloram and tebuthiuron sprays at 1.12 and 2.24 kg/ha were highly effective in reducing weed cover regardless of date of application (Table 3). After 180 days, picloram and tebuthiuron sprays of 1.12 and 2.24 kg/ha applied in January, May, July, and September 1975 significantly reduced weed cover (Table 5). Pelleted herbicides were effective in reducing weed cover at most rates of application in May, July, and September 1975 (months of highest rainfall) but were ineffective at other dates (below normal rainfall) of application (Table 4). The weed cover increased dramatically, compared with the untreated areas, at some dates of application by 180 days after treatment. Treatments showing the greatest weed recovery were tebuthiuron and picloram sprays and pellets applied at 0.37 kg/ha in October and November 1974 and picloram pellets applied at 1.12 kg/ha in October and November 1974 (Table 5). After 1 year, with some exceptions, the residual activity of most herbicides was not apparent in reducing weed cover (data not shown). Some significant reductions in weed cover occurred in November 1974 and January and March 1975. In the November 1974 and January 1975 treatments, however, differences between the untreated and treated plots, although sometimes significant, were small. In the March 1975 treatment, reductions in weed cover occurred with tebuthiuron spray at 1.12 kg/ha and picloram pellets at 1.12 and 2.24 kg/ha. Bermudagrass cover: None of the herbicides resulted in an increase in bermudagrass cover when evaluated 6O or 180 days after treatment.(data not shown). Reductions in bermudagrass cover occurred from sprays of picloram at 1.12 kg/ha applied in October 1974 and March 1975 and picloram pellets applied at 2.24 kg/ha in March 1975, 6O days after treatment (data not shown). After 180 days, sprays of tebuthiuron at 1.12 kg/ha applied in October and November 1974 and picloram at 1.12 kg/ha applied in October reduced bermudagrass cover. Reduction of grass cover occurred only from the May 1975 application after 1 year (Table 6). Picloram sprays applied at 1.12 kg/ha and all rates of picloram pellets reduced bermudagrass cover. Also tebuthiuron pellets at 0.37 7 and 2.24 kg/ha reduced bermudagrass cover when applied in May 1975. Thus, reduction of bermudagrass cover by herbicides regardless of time after application was infrequent. Bermudagrass cover increased after 1 year following spray of tebuthiuron at 2.24 kg/ha applied in October 1974. No other treatments produced significant increases in bermudagrass cover (Table 6). Sandy Site Need cover: On the sandy site, most herbicide treatments were effective in reducing weed cover 60 days after treatment (Table 7). The most effective herbicides applied in October and November were sprays of picloram and tebuthiuron at 1.12 and 2.24 kg/ha. Pelleted picloram or tebuthiuron applied in October at 0.37 and 1.12 kg/ha were ineffective. Most treatments applied in January, March, May, July, August, and September were effective, but not all weed cover was eliminated especially in the pelleted herbicide treatments applied in the fall through early spring. The area receiving the lowest rate of pelleted picloram and tebuthiuron applied in March (limited rainfall) had more weed cover than the untreated areas. In general, herbicide sprays were more effective than pellets in reducing weed cover. However, the full effect of the pelleted herbicides may not have been realized at the 60-day evaluation, especially during the time when weeds were relatively dormant (fall and winter) and rainfall amounts were below normal. After 180 days, most of the October and November treatments did not effectively control weeds (Table 8). All areas receiving herbicides in October had at least the same weed cover as the untreated areas. Tebuthiuron spray at 2.24 kg/ha was the only November treatment showing any residual weed control. Most herbicides controlled weeds when treated in January, March, May, July, August, and September (Table 8). One year after treatment, weed cover was less in all herbicide treatments applied in October, November, January, March, and May (Table 9). No differences occurred between the untreated plots and those treated in July, August, and September. Bermudagrass cover: After 60 days, October sprays of picloram at 1.12 and 2.24 kg/ha significantly reduced bermudagrass cover, compared with untreated areas, whereas all sprays of tebuthiuron and the pelleted formulations of picloram and tebuthiuron at O.37 and 2.24 kg/ha increased grass cover (Table 10). when applied in November, picloram and tebuthiuron sprays at 1.12 and 2.24 kg/ha increased grass cover. January sprays of picloram at O.37 and 2.24 kg/ha and tebuthiuron at 1.12 and 2.24 kg/ha had more bermudagrass cover than the untreated areas. Spray and pelleted picloram at 2.24 kg/ha applied in March reduced grass cover, but sprays of tebuthiuron at O.37 and 1.12 kg/ha enhanced grass cover. May applications of picloram sprays at O.37 kg/ha and sprays of tebuthiuron at O.37 and 1.12 kg/ha resulted in more grass than in the untreated area. Herbicide treatments in July, August, or September had little effect on bermudagrass cover (Table 10). 8 After 180 days, treatments that produced increased bermudagrass cover included November applications of picloram spray at 2.24 kg/ha, tebuthiuron sprays at 1.12 and 2.24 kg/ha, and pellets of picloram and tebuthiuron at 2.24 kg/ha (Table 11). January sprays of picloram at 0.37 kg/ha, tebuthiuron sprays at all rates, and picloram pellets at 2.24 kg/ha also increased bermudagrass’ cover. Treatments in March, May, July, August, and September usually had no effect on bermudagrass cover compared to the untreated areas. After 1 year, November and March picloram sprays at 2.24 kg/ha and March and May tebuthiuron sprays at 1.12 kg/ha resulted in more bermudagrass than other treatments (data not shown). Other herbicide treatments or dates of application did not affect bermudagrass cover. Residual effects of the herbicides had essentially disappeared 1 year after treatment. Effect of Double Application on weed and Grass Cover Clay Site weed cover: Sixty days after a retreatment applied 6 months after the original treatment, sprays of picloram or tebuthiuron usually reduced weed cover on areas retreated in May, September, and December 1975 and January and March 1976 (Table 12). However, sprays of tebuthiuron at 0.37 kg/ha retreated in March, July, September, and December did not reduce weed cover at 60 days after treatment. Pelleted picloram at 1.12 and 2.24 kg/ha also reduced weed cover when retreated in May, September, and December 1975, and January and March 1976. Pelleted tebuthiuron at 1.12 kg/ha retreated in September 1975 and January and March 1976 reduced weed cover as well as 2.24 kg/ha retreated in May, September, and December 1975, and January and March 1976 (Table 12). After 180 days, all sprays of picloram and tebuthiuron retreated in May, September, and December 1975 reduced weed cover (Table 13). Picloram and tebuthiuron sprays at 1.12 and 2.24 kg/ha retreated in July 1975 also significantly reduced weed cover. After 180 days, all pelleted picloram rates retreated in May and December 1975 and picloram at 2.24 kg/ha retreated in July and September 1975 reduced weed cover. Pelleted tebuthiuron at 1.12 and 2.24 kg/ha effectively controlled weeds when retreated in May, July, September, and December 1975 (Table 13). After 1 year, most retreatments did not control weeds (data not shown). Bermudagrass cover: None of the herbicides was consistently effective for increasing or decreasing the grass cover on the clay site 60, 180, or 365 days after retreatment (data not shown). Sand! Site Need cover: Sprays of picloram and tebuthiuron at all rates and dates of retreatment significantly reduced weed cover after 60 days on the sandy site except tebuthiuron at 0.37 kg/ha retreated in March 1975 (Table 14). Pelleted picloram and tebuthiuron were also highly effective in reducing weed cover at most rates and dates when retreated in May, July, September, and December 1975, 9 and January and March 1976. Retreatment with pelleted tebuthiuron at 2.24 kg/ha was the only pelleted herbicide effective when applied in March 1975 (Table 14). After 180 days, most herbicide retreatments were effective in reducing weed cover when applied in March, May, July, September, and December 1975 (Table 15). After 1 year, however, only picloram sprays at 1.12 and 2.24 kg/ha were effective as retreatments applied in March and May 1975 (data not shown). Results for tebuthiuron sprays 1 year after retreatment were erratic. Areas retreated after May 1975 had poor weed cover in treated and untreated areas, so differences between treatments were small. Bermudagrass cover: After 60 days, grass cover increased where tebuthiuron spray was retreated at 0.37 kg/ha in March 1975, 1.12 kg/ha in May 1975, 0.37 and 1.12 kg/ha in July 1975, and 1.12 kg/ha in March 1976 (Table 16). Increases in grass cover also resulted from retreatment of tebuthiuron pellets at 2.24 kg/ha in May 1975 and at 1.12 kg/ha in March 1976. After 180 days, tebuthiuron sprays at 2.24 kg/ha retreated in May 1975 and 1.12 kg/ha retreated in September and December 1975 were the only treatments that increased grass cover. Pelleted herbicides were ineffective (data not shown). After 1 year, significant grass cover increases occurred in several retreatments made in May, July, and September 1975 (Table 17). Picloram and tebuthiuron applied as sprays at 2.24 kg/ha doubled grass cover when retreated in July and September 1975. Picloram and tebuthiuron retreated as sprays and pellets in July 1975 at 0.37 kg/ha also increased grass cover. Picloram sprays at 2.24 kg/ha retreated in May 1975 were also highly effective in increasing bermudagrass cover 1 year after retreatment. Results of all Treatments on weed Populations Data on the effects of single and retreatment applications on the composition of the broadleaf weed population 1 year after the last application were grouped and evaluated on a seasonal basis. Examination of the data on this basis negated the natural effects of season on population composition. The seasons are designated spring (March through May) and winter (October through February). Composition data from the plots treated (and retreated) with the 1.12 and 2.24 kg/ha rate of both formulations (spray and pellet) of picloram and tebuthiuron are considered. Spring application of 1.12 and 2.24 kg/ha of both formulations of tebuthiuron and picloram removed 12 species from the sandy site: burclover, white clover, evening primrose, false dandelion, milkweed, phacelia, poorjoe, rush spp., scarlet pimpernel, sedge spp., sida, and toadflax (Fig. 1). 7\Similarly, 10 species were removed from the clay site: burclover, chickweed, crow poison, dichondra, false dandelion, indian paintbrush, smartweed, toadflax, vervain, and wild celery (Fig. 1). Horseweed and ragweed were 10 controlled by the two higher rates of picloram treatments on the sandy site, whereas on the clay site 2.24 kg/ha rate of both formulations was required to remove ragweed; horseweed was removed only by the high rate of picloram spray. The high rate of tebuthiuron pellets was necessary to remove horseweed from the sandy site, whereas all rates of both spray and pellets removed it from the clay site. The high rate of both formulations of tebuthiuron was necessary to remove ragweed from the clay site, whereas on the sandy site all rates of pellets and the high rate of spray were required. Geranium was controlled by both rates of sprays of picloram but not pelleted picloram at 1.12 kg/ha on the sandy site. Only the high rate of pelleted picloram controlled geranium on the clay site. Horsemint was controlled by the higher rates of picloram spray on the clay site and pellets on the sandy site. There were several instances where only the high rate (2.24 kg/ha) of pelleted picloram resulted in control: sensitive briar, scarlet pimpernel, white clover, and butterweed on the clay site and phlox, indian paintbrush, and dock on the sandy site. Application of all treatments in the winter removed eight species from the sandy site: aster, burclover, curly dock, evening primrose, horsemint, ragweed, vervain, and winecup (Fig. 2). Similarly, three species were removed from the clay site: chervill, dichondra, and plantain. Dewberry and wood sorrel were removed from the sandy site by both rates of the spray formulation of both herbicides. wood sorrel on the clay site was unaffected by tebuthiuron spray and 1.12 kg/ha tebuthiuron (Fig. 2). Ragweed was eliminated by all picloram treatments on both sites and.by all tebuthiuron treatments on the sandy site. Tebuthiuron at 2.24 kg/ha as pellets or sprays killed all ragweed on the clay site. Vetch was eliminated on the sandy site by all treatments except tebuthiuron sprays at 1.12 kg/ha. The major observation noted for the retreatment data for both sites (Fig. 3) is a rate effect. On the sandy site, control of curly dock, milkweed, phlox, and vervain occurred on all spring treatments. Evening primrose and indian paintbrush were controlled by all spring treatments of tebuthiuron and picloram, respectively. The remaining species were generally controlled by the 2.24 kg/ha rate of all treatments. A much greater degree of control was noted for all species on the clay site. A strict numerical analysis of species controlled by a given formulation or herbicide reveals that picloram had a slight edge over tebuthiuron in percentage of spring species controlled on the sandy site (64 vs. 58 percent); the two herbicides were equivalent in control of spring species on the clay site (63 vs. 59 percent) and winter species on the sandy site (74 vs. 77 percent). Picloram was decidedly superior to tebuthiuron in control of winter species on the clay site (84 vs. 62 percent). Percentage of species controlled relative to formulation indicated that spray applications were slightly better than pellet applications. The results of the plant surveys after application of herbicides indicated that a large number of species can be eliminated from the treated area, allowing a potential increase in grass production. 1. 2O 3Q 10. 11. 12. 13. 14. 15. 11 LITERATURE CITED Baur, J. R. 1978. Movement in soil of tebuthiuron from sprays and granules. Tex. Agr. Exp. Sta. PR-3524. 14 pp. Baur, J. R., R. N. Bovey, and E. C. Holt. 1977. Effect of herbicides on production and protein levels in pasture grasses. Agron. J. 69:846-851. Bovey, R. w., F. S. Davis, and H. L. Morton. 1968. Herbicide combinations for woody plant control. Weed Sci. 16:332-335. Bovey, R. W., C. C. Dowler, and M. G. Merkle 1969. movement of picloram in Texas and Puerto Rican soils. Monitoring J. 3:177-181. The persistence and Pesticide 1974. Tolerance of J. Range Manage. 27:293-296. Bovey, R. H., R. E. Meyer, and E. C. Holt. bermudagrass to herbicides. Control of huisache with soil 31:179-181. 1978. J. Range Manage. Bovey, R. W., and R. E. Meyer. applied herbicides. Bovey, R. N., E. Burnett, R. E. Meyer, C. Richardson, and A. Loh. 1978. Presistence of tebuthiuron in surface runoff water, soil and vegetation in the Texas Blacklands Prairie. J. Environ. Qual. 7:233-236. Bovey, R. W., R. E. Meyer, and H. Hein, Jr. 1982. tebuthiuron in the Claypan Resource Area of Texas. Soil persistence of Weed Sci. 30:140-144. Chang, S. S., and J. F. Stritzke. 1977. dissipation of tebuthiuron in soils. Weed Sci. Sorption, movement, and 25:184-187. 1970 Manual of the Vascular Plants of 1881 pp. Correll, D. S., and M. C. Johnston. Texas. Tex. Res. Found., Renner, TX. Council of Agricultural Science and Technology (CAST). 1975. herbicides. Weed Sci. 23:253-263. The phenoxy Fischer, M. L., and J. F. Stritzke. 1978. properties on phytotoxicity of tebuthiuron. 31:204. Effects of various soil Proc. South weed Sci. Soc. Garcia, J. 0., and B. D. Gontarek. 1976. Residues of the herbicide EL-103 in west Texas rangeland 14 months after application. Noxious Brush and Need Res. Highlights 6:10. Texas Tech. Univ., Lubbock, TX. Grover, R. 1968. 4-amino-3,5,6-trichloropicolinic acid (picloram). Influence of soil properties on phytotoxicity of weed Res. 8:226-232. Herr, D. E., E. W. Stroube, and D. A. Ray. 1966. The movement and persistence of picloram in soil. Weeds 14:248-250. ' 16. 17. 18. 19. 20. 21. 22. 12 Kaufman, D. D. 1974. In: Pesticides in soil and water. s51. Soc. of Ameri., Madison, m. Degradation of pesticides by soil microorganisms. wo D0 Eda p0 Mayeux, H. S., Jr. 1986. A comparison of herbicide sprays and pellets for control of broadleaf weeds in pastures. (Abstr.) Weed Sci. Soc. Am. page 38. Merkle, M. G., R. W. Bovey, and F. S. Davis. persistence of picloram in soil. Agron. J. 1967. Factors affecting the 59:413-414. Control of an oak 26:444-453. Meyer, R. E., R. W. Bovey, and J. R. Baur. 1978. (Quercus) complex with herbicide granules. weed Sci. Novosad, A. C., J. E. Cole, E. C. Holt, R. D. 1973. Suggestions for weed control with chemicals. Sta. MP-1060, Part II, p. 6-7. Palmer, and J. N. Pratt. Tex. Agric. Exp. Herbaceous vegetation changes J. Range Scifres, C. J., and J. L. Mutz. 1978. following applications of tebuthiuron for brush control. Manage. 31:375-378. Steel, R. G. D., and J. H. Torrie. 1960. Principles and procedures of statistics. New York: McGraw-Hill. 481 pp. All programs and information of The Texas Agricultural Experiment Station are available to everyone without regard to race, color, religion, sex, age, handicap, or national origin. Mention of a trademark or a proprietary product does not constitute a guarantee or a warranty of the product by The Texas Agricultural Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. ‘ 2 13 SANDY SITE TEBUTHIURON PREDOMINANT seem I PELLET SPECIES RATE (kg/ho) 1.12 2.24 1.12 2.24 L Blaclteyed susan Burclover F Chicttvieed ¥Uwn,wmh Croe poison Dewberry CDotk. curly Evening primrose FIISI dandelion Geranium l-lorseweed ‘K140301111!!! Indian paintbrush Milkweed Phacel la Frmw Plantain map. E Queen Anne's lace Ragweed 1W RUSh Sarlet pimpernel s» fiSidi I Spring beauty lldlli! Vervain Evmm Immtmuy Fnmump Tripod sorrel FIGURE 1. 3! application. PlCLQRAM senmr PELLET RATE (liq/not 1.12 2.24 n2 2 I e:o'e:o:e ---- -. . .-.;.;. CLAY SITE PREDOMINANT SPECIES TEBUTHIURON PICLORAM SPRAY PELLET SPRAY PELLET RATE (liq/lid) RATE (kg/rial 112 2.24 112 2.24 1.12 2.2 1.12 2.2 Blaclteyed susan Burclover Buttervveed Chicltvveed Clover, white Cron poison Dandelion Dlchondra Dock. curly Evening primrose False dandelion Geranium Horsemint Horseweed Indian paintbrush Plantain Ragweed Scarlet pimpernel Sensitive briar Smarlweed Sou thistle Sunflower Tlcltseed Toadllax Vervaln Wild celery W000 sorrel Spring evaluation of weed composition 1 year after a single All listed weeds occurred in control plots. p areas indicate the occurrence of the noted species. Darkened Data for each species represents a composite of 12 replicate treated areas. 14 SANDY SITE CLAY SITE TEBUTHIURON P1CLORAM TEBUTHIURON P1CLORAM PREDOMINANT seam [PELLET senav PELLET PREDOMINANT seeav [PELLET seem PELLET SPECIES an: (kg/ho) ears (kg/ho) SPECIES ens (kg/ha) an: (ho/ho) 1.12 2.24 1.12 2.24 1.12 2.24 1.12 2 1.12 2.24 1.12 2.24 1.12 2.24 1.12 2.24 Astor Chervil Bllrdwlf Croton. woody Dam"? Dicnondra 9°“- ¢""'Y 51191111"! P71111793! 5555525535 Evening primrose Geranium Geranium Modiola Horsomini Piantain Plantain Ragvieod Ragweed wood sorrel Vorvain Vetcn Wild celery Winocup W“! SUYH FIGURE 2. Winter evaluation of weed composition 1 year after a sing1e app1ication. A11 listed weeds occurred in control p1ots. Darkened areas indicate the occurrence of the noted species. Data for each species represents a composite of 18 replicate treated areas. A 15 SANDY SITE CLAY SITE TEBUTHIURON PICLORAM TEBUTHIURON PICLORAM PREDOMINANT swam PELLET senor PELLET PREDOMlNANT senav PELLET semw wetter SPECIES RATE (liq/ho) an: lkg/hol SPECIES were (kg/ho) RATE (kg/ho) 1.12 2.24 n2 2.24 112 2.24 n2 2.24 1.12 2.24 n2 2.24 112 2.24 I 12 2.24 Chicllweed 1% Blackeyed susan Qfg BUQIIWOOC Oqqngrry . __ Dandelion Doct, curly Dichondra primrose Evening primrose lfii-‘i Geranium -" 4 .1 -~ ' Y Hllfflfllifli Hqgamim O Plantain Indian paintbrush Z Ragweed "f? Milkweed E Sensitive briar :25. Phlox 0 Sou thistle Plantain .._' ,--‘-- * 1 - - Sunflower gf-Yff ‘ Rm“ .. .. . Spring beauty Vervain Vetch Wild celery . . Chervil Dock, Clover, white Evening primrose Croton. W004i! False dandelion . Crow D0550" Geranium Dandelion Croton, voooly ' m Dichondra Goosegrass h] Dock. curly Plantain E Evening primrose Rush — Geranium yum 3 Modiola mm Plantain wlnecup _ RIJWM wannmu '1 . U aimau Sunflower Ticlnseed Wood sorrel FIGURE 3. Spring and winter evaluations 1 year after a retreatment application. All listed weeds occurred in control plots. Darkened areas indicate the occurrence of the noted species. Data for each 7* species represents a composite of nine replicate treated areas. L6 Table 1. Common and scientific names of weed species found throughout the two study sites (common name synonyms in parentheses) Common Scientific Aster, white heath Blackeyed-susan Butterweed Burclover spp. Chervil Chickweed common mouseear Clover, white Croton, woolly Crow poison Dandelion, common Dewberry, southern (Zarza mora) Dichondra (Pony foot) Dock, curly (Yellow) Evening primrose spp. False dandelion, Carolina Geranium, Carolina Goosegrass _ Horsemint (Spotted beebalm) Horseweed‘(Marestail) Aster pilosus willd. Rudbeckia serotina Nutt. Sénecio glabellus Pair. Medicago spp. Chaerophyllum tainturieri Hook. Stellaria media (L.) Cyrillo Cerastium vulgatum L. Trifolium repens L. Croton capitatus Michx. Nothoscordum bivalve (L.) Britt. Taraxacum officinale Weber Rubus trivialis Michx. Dichondra spp. Rumex crispus L. Oenothera spp. Byrrhopappus carolinianus (walt.) D. C. Geranium carolinianaum L. Eleusine indica (L.) Gaertn. Monarda punctata L. Conyza canadensis (L.) Cronq. ~L Table 1. (Continued) 17 Common Scientific Indian paintbrush (Painted cut) Milkweed, orange (Butterfly-weed Chigger-flower) Modiola Phacelia Phlox spp. Plaintain spp. buckhorn english (Ribwort) Poorjoe (Rough buttonweed) Queen Anne's lace (wild carrot) Ragweed, short (Common) (Altamisia) Ragwort (Texas groundsel) Rush spp. Scarlet pimpernel Sedge spp. Sensitive briar Sida (Prickly mallow) Smartweed, Pennsylvania Sow thistle Spring beauty Sunflower, common Castilleja spp. Asclepias tuberosa L. Modiola caroliniana (L.) G. Don. Phyacelia glabra Nutt. Phlox spp. Plantago aristata Michx. Plantago lanceolata L. Diodia teres Walt. Dacus carota L. Ambrosia artemisiifolia L. Senecio ampullaceus Hook. Juncus spp. Anagallis arvensis L. Carex spp. Schrankia spp. Sida sginusa L. Polygunum pensylvanicum L. Sonchus spp. Claytonia virginica L. Helianthus annuus L. Table 1. (Continued) 18 Common Scientific , Tickseed Coris permum spp. Toadflax, Texas . Vervain, blue Vetch, narrowleaf Wild celery Winecup woodsorrel, yellow Linaria texana Scheele. Verbena hastate L. Vicia augustifolia L. Apium graveolens L. Callirhoe digitata Nutt. Oxalis priceae Small. Names taken from Correll and Johnston (10). 19 Table 2. Dates of application of original treatments and retreatments and month when the 60-, 180-, or 365-day post-treatment or retreatment evaluations were made Original Post-treatment evaluation (days) treatment Retreatment 60 180 365* October 1, 1974 Dec Apr Oct March 17, 1975 May Sep Mar November 20, 1974 Jan May Nov May 19, 1975 Jul Nov May January 29, 1975 Mar Jul Jan July 29, 1975 Sep Jan Oct (446) March 23, 1975 May Sep Mar September 23, 1975 Nov Mar Oct (396) May 27, 1975 “ Jul Nov May December 3, 1975 Feb Jun Oct (328) July 1, 1975 Sep Dec Oct (474) December 28, 1975 Feb Nov (320) August 1, 1975 Oct Feb Nov (443) January 1, 1976 Mar Oct (261) September 17, 1975 Dec Apr Nov (396) _ March 18, 1976 May Oct (210) *Exceptions in parentheses. ~41 Table 3. Weed cover (percent) 60 days after a single application of spray or pelleted 20 picloram or tebuthiuron at three rates at the clay site, Bryan, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-2375 5-27-75 7-1-75 8-1-75 9-1-75 §_P_"éx ' Picloram 0.37 17cde 13ef 36de 3b 2c lb 3w 6b Picloram 1.12 3e 6f 3g Ob Oc Ob Od 2b Picloram 2.24 Oe Of Og Ob Oc Ob Od Ob Tebuthiuron 0.37 50ab 29de 39d 43a 8abc 3b 12abcdl 3b Tebuthiuron 1.12 11de _ 12ef 14fg 3b 1c Ob 4cd 3b Tebuthiuron 2.24 Oe 6f 9fg Ob Oc Ob 1d ' Ob EflLiE Picloram 0.37 47ab »- 64abc 70ab 58a 20a 16a 17ab 4b Picloram 1.12 36bc 58bc 55bc 43a 3bc 3b lcd 4b Picloram 2.24 25cd 33de 22ef 14b 1c 3b 9bcd 3b Tebuthiuron 0.37 50ab 83a 66ab 63a 16a 17a 21a 13a Tebuthiuron 1.12 36bc 78ab 63b 42a 8abc 6b 4cd 5b Tebuthiuron 2.24 llde 49cd 47cd 40a 9abc Ob Scd 2b" Untreated 66a 75ab 81a 15b 15ab 21a 13abc 18a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 21 Table 4. Rainfall (cm) near the experimental sites (College Station, Texas, Easterwood Airport) from January 1, 1974, to January 1, 1976 Month 1974 1975 1976 Rainfall Dev. from Rainfall Dev. from Rainfall Dev. from A normal normal normal January 12.27 5.77 5.46 -1.04 3.00 -3.51 February .25 -7.70. 6.48 -1.47 2.97 -4.98 March 4.60 -1.96 3.68 -2.87 9.30 2.74 April 8.03 -2.51 7.95 -2.59 15.37 4.83 May 3.51 -6.32 24.79 13.69 15.09 3.99 June 2.51 -6.81 5.82 -3.43 7.04 -2.21 July 5.05 -1.45 10.92 4.42 9.65 3.15 August 27.00 20.32 5.13 -1.55 4.45 -2.24 September 25.20 14.55 11.05 .41 8.92 -1.73 October 15.19 7.52 9.86 2.18 14.27 6.60 November 15.21 7.21 2.57 -5.44 9.09 1.09 December 6.63 -1.57 2.82 -5.38 10.59 2.39 Total 126.72 27.13 96.52 -3.07 109.73 10.13 Taken from Climatological Data, U.S. Department of Commerce, National Climatic Center, Federal Building, Asheville, NC. (College Station, Texas, Easterwood Airport) .-\ .» i Table 5. weed cover (percent) 180 days after a single application of spray or pelleted 22 picloram or tebuthiuron at three rates at the clay site, Bryan, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 £2221 Picloram 0.37 61ab 60abc 9ab Oc 2bc 3bc 4oc 33abc Picloram 1.12 33cde 21d 2b 2c 1c 3bc 3bc 14de Picloram 2.24 23def 15d 3b 0c 0c 1c 30¢ 3e Tebuthiuron 0.37 75a 49bcd 10ab 3c Oc 3bc 5bc 35ab Tebuthiuron 1.12 23def 24cd 3b Jc 2bc Oc 4bc 14de Tebuthiuron 2.24 6f 17d lb yc Zbc 1c Oc Oe £21123 Picloram 0.37 71a 87a 10ab 25a 8b 66c "8abc 43a Picloram 1.12 61ab 62ab 10ab 8abc 2bc 3bc 4bc 24bcd Picloram 2.24 39cd 47bcd llab 2c 3bc 1c 3bc 20bcd Tebuthiuron 0.37 71a 91a llab 22ab 6bc 7ab 14a 25ocd Tebuthiuron 1.12 61ab 42bcd 16a 13abc 3bc 4bc 9ab l8cde Tebuthiuron 2.24 45bc 28bcd 8ab Sbc 1c 1c 3bc 20bcd Untreated 15ef 15¢ 15a. 13abc 18a 11a 8bc 42a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 23 Table 6. Bermudagrass cover (percent) 365 days after a single application of spray or pelleted picloram or tebuthiuron at three rates at the clay site, Bryan, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 £212.! ' 2mm?” 0.37 2a..» 70a 25.? 40.» as.» 52.» 4a.» 50a.» Picloram 1.12 18c - 37a 37ab 18b 55a 30a 20ab Picloram 2.24 75ab 77a 47a 22b 25ab 30a 42a 17ab 7ebuthiuran '0.37 33¢ 75a 35a 84255 38ab 50a 60a 53a0 Tebuthiuron 1.12 15c - 42a 50ab 33ab 57a 28a 28ab Tebuthiuron 2.24‘ 90a 55a 40a 4m‘ 22ab 30a 35a 10b 2&8}. Picloram 0.37 45bc 53a 37a 40ab 12b 10a 20a 45ab Picloram 1.12 45bc 57a 32a 77a 13b- 23a 52a 43ab Picloram 2.24 28c 40a 38a 42ab 7b 33a 65a 40ab Tebuthiuron 0.37 52abc 63a 30a 58ab 13b 5a 30a 60a Tebuthiuron 1.12 50bc 35a 18a 52ab 20ab 30a 62a 40ab Tebuthiuron 2.24 43bc 55a 48a 45ab 12b 43a 65a 30ab Untreated 49bc 66a 48a 53ab 55a 38a 38a 38ab Means within each column followed by the same letter do not differ significantly at ¢;he 5 percent level using Duncan's multiple-range test. Table 7. picloram or tebuthiuron at three rates at the sandy site, wellborn, 24 Texas weed cover (percent) 60 days after a single application of spray or pelleted Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 Spraz A Picloram Picloram Picloram Tebuthiuron Tebuthiuron Tebuthiuron E112}. Picloram Picloram Picloram Tebuthiuron Tebuthiuron Tebuthiuron Jntreated I} 0.37 1.12 2.24 0.37 1.12 2.24 0.37 1.12 2.24 0.37 1.12 2.24 41bc 12d 14d 39c 34cd 20cd 72a 61ab 39c 75a 66a 33cd 78a 44de 17f 11f 50cde 30ef 11f 69bc 66bc 43de 72bc 75b 61bcd 96a Date of treatment 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 25ef 26ef 23f ' 20f 25f 14f. 68b 47cd 31def 72ab 61bc 45cde 89a 10cd 8cd 2d 18bcd 4d 2d 58a 23bcd 23bcd 67a 33bc 9cd 35b lb 2b lb lb 3b 6b 3b 3b lb 4b 3b 3b 35a 4bc 1c 2c 3c 3c 5bc 5bc 4bc 3c 9b 7bc 1c 22a 3bc 3bc 2bc 3bc 3bc 7b 4bc 3bc 0c 4bc 3bc 4bc 17a 3bc 3bc 3bc 2bc 3bc 0c 3bc 3bc 5b 5b 3bc 3bc 13a leans within each column followed by the same letter do not differ significantly at zhe 5 percent level using Duncan's multiple-range test. 25 Table 8. Need cover (percent) 180 days after a single application of spray or pelleted picloram or tebuthiuron at three rates at the sandy site, Nellborn, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 £2211 Picloram 0.37 58bcd 49abcd 3b 7bc 5bc 13b 13b 14cde Picloram 1.12 41de 13ef 4b 2cd 2c 7b 10b 8e Picloram 2.24 30ef 13ef 8b Sbcd 10ab 8b 9b 6c Tebuthiuron 0.37 61bc 63abc 2b 7bc 3c 11b 12b 23bcd Tebuthiuron 1.12 56cd 11ef 2b 0d 3c 6b ~5b 13de Tebuthiuron 2.24 22f 4f lb 5bcd 3c 7b 5b 7e B21122 Picloram 0.37 81a 68a 4b 7bc 6bc 13b 15b 28b Picloram 1.12 69abc 86ab 3b 7bc 6bc 10b 12b 25bc Picloram 2.24 69abc 26def 6b 5bcd 5bc 13b 7b 13de Tebuthiuron 0.37 77ab 64ab 3b 7bc 4bc 14b 15b 33b Tebuthiuron 1.12 66abc 38bcde so an 13¢ 10b 15b 27b Tebuthiuron 2.24 66abc 13ef 6b 2cd 3c 9b 13b 13de Untreated 35ef 35cde 35a 19a 13a 32a 28a 44a Means within each column followed by the same letter do not differ significantly at -the 5 percent level using Duncan's multiple-range test. 26 Table 9. Weed cover (percent) 365 days after a single application of spray or pelleted picloram or tebuthiuron at three rates at the sandy site, Wellborn, Texas Date of treatment Herbicide Rate' formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 £221 Picloram 0.37 7bc 3bc 15b 27bc 40bc 8a 7a 8a Picloram 1.12 3bc 0c 12b 15cd 43bc 5a 12a 8a Picloram 2.24 7bc 0c 13b 11d 18d 5a 5a 5a Tebuthiuron 0.37 10b 3bc 16b 28bc 43bc 8a 7a 8a Tebuthiuron 1.12 2c 2c 10b 18bcd 33bcd' 5a 8a 10a Tebuthiuron 2.24 8bc Oc 12b 32b 50b 5a 5a 7a BEBE Picloram 0.37 10b 2c 8b 30b 37bc 13a 5a 8a Picloram 1.12 7bc Oc 12b 25bcd 43bc 7a 13a 8a Picloram 2.24 _ 5bc 2c 12b 25bcd 40bc 13a 8a 5a Tebuthiuron 0.37 7bc 8b 10b 28bc 40bc 8a 7a 8a Tebuthiuron 1.12 8bc 3bc 15b 27bc 30cd 5a 13a 7a Tebuthiuron 2.24 7bc 3bc 8b 27bc 27cd 7a 7a 5a Untreated 17a 14a 28a 44a 72a 9a 9a 9a Means within each column followed by the same letter do not differ significantly at. the 5 percent level using Duncan's multiple-range test. Table 10. 27 Bermudagrass cover (percent) 60 days after a single application of spray or pelleted picloram or tebuthiuron at three rates at the sandy site, wellborn, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 iliél ‘ Picloram 0.37 60cde 63abc 58a 52bc 76a 53a 70ab 82a Picloram 1.12 18g 79a 48abc 22de 64ab 55a 55bcd 78a Picloram 2.24 32g 77ab 65a 8e 48b 45a 45cd 78a Tebuthiuron 0.37 83abc 63abc 57ab 78a 76a 55a 78a 73a Tebuthiuron 1.12 84ab 78ab 62a 73ab 77a 53a 58bcd 73a Tebuthiuron‘ 2.24 76abcd 80ab 67a 40cd 63ab 37a 44d 72a Bélléi Picloram 0.37 92a 57bc 46abc 42cd 51b 52a 63abc 77a Picloram 1.12 54de 69abc 45abc 41cd 50b 48a 59bcd 78a Picloram 2.24 67bcd 72abc 51abe 14e 47b 47a 62abcd. 75a Tebuthiuron 0.37 93a 58abc 28c 52bc 58ab 53a 64ab 75a Tebuthiuron 1.12 58de 65abc 53ab 53bc 50b 48a 68ab 78a Tebuthiuron 2.24 77abcd 73abc 49abc 48c 55ab 45a 80a 73a Untreated 42ef 54c 33bc 44cd 44b 48a 63abc 73a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 2. l Table 11. Bermudagrass cover (percent) 180 days after a single application of spray or pelleted picloram or tebuthiuron at three rates at the sandy site, wellborn, Texas Date of treatment Herbicide Rate formulation(kg/ha) 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 2E2): Picloram 0.37 28a 50cd 73ab 75a 79a 80a 68a 72a Picloram 1.12 38a 63bcd 69abc 68a 4 74ab 73ab 58abc 62a Picloram 2.24 23a 73abc 63abc 72a 59bc 83a 45cd 67a Tebuthiuron 0.37 39a 43d 78ab 72a 78a ‘75ab 68a 66a Tebuthiuron 1.12 41a 78ab 86a 88a 70ab 58bc 50bcd 62a lebuthiuron 2.24 33a 95a 85a 63a 78a 35a 35a 57a Elk}. Picloram 0.37 33a 52cd 68abc 88a 76ab 74ab 62abe 66a Picloram 1.12 28a 43d 59abc 68a 73ab 80a 50abcd 63a Picloram 2.24 32a 72abc. 57b 57a 53¢ 725p 60abc 57a Tebuthiuron 0.37 31a 47cd 65abc 92a 78a 77a 52abc 58a Tebuthiuron 1.12 26a 63bcd 63abc 63a 78a 72ab 50bcd 60a Tebuthiuron 2.24 39a 79ab 61abc 62a 76ab 55c 48bcd 67a Untreated 44a 44d 44c 63a 73ab 68abc _63ab 61a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 29 Table 12. weed cover (percent) 60 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the clay site, Bryan, Texas Date of original treatment & retreatment Herbicide Rate 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 _formulation(kg/ha) 3-17-75 5-19-75 7-29-75 9-23-75 12-3-75 12-28-75 1-1-75 3-18-75 éem Picloram 0.37 2b 2d Ob 3b Ob Ob 2c Oc Picloram 1.12 Ob Od Ob 2b Ob 10b Oc Oc Picloram 2.24 Ob Od Ob 2b Ob Ob Oc Oc Tebuthiuron 0.37 23b '3d Ob 17a 2ab 15ab 10c 5c Tebuthiuron 1.12 Ob 2d Ob Ob Ob 13b Oc Oc Tebuthiuron 2.24 Ob 2d Ob Ob Ob Ob Oc Oc £91493. Picloram 0.37 67a 47a 5ab 5b 3ab 17ab 27b 43a Picloram 1.12 18b 3d 18a Ob 2ab 7b 3c 2c Picloram 2.24 15b Od 12ab Ob 2ab 5b 2c Oc Tebuthiuron 0.37 80a 27b 7ab 17a 8a 18ab 37ab 23bA Tebuthiuron 1.12 17b 12c 3ab Ob Sab 17ab 12c 2c Tebuthiuron 2.24 12b Od Sab 2b Ob 2b Oc Oc Untreated 15b 15c 13ab 19a 8a 42a 42a 58a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. Table 13. 30 weed cover (percent) 180 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the at the clay site, Bryan, Texas Date of original treatment & retreatment 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 Herbicide Rate formulation (kg/ha) 3-17-75 5-19-75 7-29-75 9-23-75 12-3-75 2E1 Picloram 0.37 Oc 2c 3a 15cd Ob Picloram 1.12 8abc Oc Ob 17cd Ob Picloram 2.24 2bc Oc Ob Oc Ob Tebuthiuron 0.37 2bc 2c 3ab 18bcd 7b Tebuthiuron 1.12 Oc 2c Ob 3cd Ob Tebuthiuron ' 2.24 Oc 2c Ob ' Od Ob 23.3.1915 Picloram 0.37 15ab 7b 3ab 37ab 18b Picloram 1.12 3bc 3c 3ab 23abc 13b Picloram 2.24 12abc Oc 2b 10cd 2b Tebuthiuron 0.37 20a 12ab 3ab 37ab 40a Tebuthiuron 1.12 3bc 2c 2b 15cd 12b Tebuthiuron 2.24 5bc Oc Ob 12cd 3b Untreated 13abc 16a 8a 42a 58a Means within each column followed by the same letter do not differ signi- ficantly at the 5 percent level using Duncan's multiple-range test. 31 Table 14. Need cover (percent) 60 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the sandy site, Wellborn, Texas Date of original treatment & retreatment Herbicide Rate 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 formulation(kg/ha) 3-17-75 5-19-75 7-29-75 9-23-75 12-3-75 12-28-75 1-1-76 3-18-76 £21! Picloram 0.37 7c 3b 2c 2c 7bc 7de 2f Sbc Picloram 1.12 5c 2b 3bc 0c 0c 3e 8ef 0c Picloram 2.24 0c Ob 3bc 0c 0c 3e 2f 0c Tebuthiuron 0.37 17bc 5b 2c 3bc 0c 17cde 17de 13bc Tebuthiuron 1.12 3c 3b Oc 0c 2c 13cde 3f 2c Tebuthiuron 2.24 Sc Ob 0c 3bc 2c 10cde 2f 2c £21123 Picloram 0.37 63a 5b 8b 5bc 15b 27bc 27bc 2c Picloram 1.12 33b 3b , 2c 5bc 12b 18cde 20cd 17b Picloram 2.24 12bc 2b 5bc 3bc 12b Sde 10def 5bc Tebuthiuron 0.37 63a 7b m 8b 13b 37ab 33b 17b Tebuthiuron 1.12 23bc 3b 3bc 3bc 12b 22bcd 32b 10bc Tebuthibron 2.24 8c 2b f 3bc 3bc 7bc 3e 20cd 5bc Untreated 35b 35a 17a 14a 28a 44a 44a 72a Means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 32 Table 15. weed cover (percent) 180 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the .at the sandy site, wellborn, Texas Date of original treatment & retreatment Herbicide Rate 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 formulation (kg/ha) 3-17-75 5-19-75 7-29-75 9-23-75 12-3-75 ilfil Picloram 0.37 5b 3b 3bc 8efg 12cd Picloram 1.12 3b 7b 8bc 09 0d Picloram 2.24 7b 0b 7bc 3fg 2d Tebuthiuron 0.37 5b 2b 3bc 15def 17cd Tebuthiuron 1.12 5b 2b 3bc 2fg 7d Tebuthiuron 2.24 7b Ob Oc 5fg 0d EH22 Picloram 0.37 _ 3b 2b 10b 27bcd 50b Picloram 1.12 7b 0b 3bc 28bc 12cd Picloram 2.24 5b 3b 8bc 18cde l8cd Tebuthiuron 0.37 3b 3b 10b 38ab 33bc Tebuthiuron 1.12 10ab 3b 7bc 27bcd 15cd Tebuthi uron 2.24 5b 3n 5m 13am 2a Untreated - 17a 14a 28a 44a 72a Means within each column followed by the same letter do not differ signi- ficantly at the 5 percent level using Duncan's multiple-range test. 33 Table 16. Bermudagrass cover (percent) 60 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the sandy site, wellborn, Texas Date of original treatment & retreatment Herbicide Rate 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 8-1-75 9-1-75 formulation(kg/ha) 3-17-75 5-19-75 27-29-75 9-23-75 12-3-75 12-28-75 1-1-76 3-18-76 £2221 Picloram 0.37 37bcd 68ab 70abc 87ab 70a 63ab 60ab 35bc Picloram 1.12 43bc 62ab 70abc 88a - 63a 38abc 33ab 37bc Picloram 2.24 2d 67ao 80abc 87ab 72a 27bc_ 35ab 38bc Tebuthiuron 0.37 88a 73ab 95a 80ab sea 73a 63ab 57ab Tebuthiuron 1.12 65ab 83a 95a 78ab 68a 32bc 43ab 77a Tebutniuron 2.24 18cd 38a 85ab 73ab 65a 12c ~ 17o 28bc E1131 Picloram 0.37 37bcd 57ab 53¢ 73ab 60a 63ab 67a 17¢ Picloram 1.12 33bcd 50ab 70abc 83ab 60a 72a 62ab 33bc Picloram 2.24 18cd 65ab 58bc 78ab 60a 53ab 63ab 10c Tebuthiuron 0.37 57abc 60ab 77abc 72b 57a 60ab 43ab 39bc Tebuthiuron 1.12 60ab 60ab 75abc 80ab 57a 60ab 57ab 78a Tebuthiuron 2.24 30bcd 80a 55bc 77ab 47a 30bc 60ab 28bc Untreated - 39bcd 43b 63bc 73ab 63a 61ab 61ab 27bc means within each column followed by the same letter do not differ significantly at the 5 percent level using Duncan's multiple-range test. 34 Table 17. Bermudagrass cover (percent) 365 days after two applications 6 months apart of spray and pelleted picloram or tebuthiuron at three rates at the sandy site, wellborn, Texas Date of original treatment & retreatment Herbicide Rate 10-1-74 11-20-74 1-29-75 3-23-75 5-27-75 7-1-75 1-1-75 9-1-75 formulation(kg/ha) 3-17-75 5-19-75 7-29-75 9-23-75 12-3-75 12-28-75 1-1-76*3-18-76 £2231 Picloram 0.37 77a 30d 75b 63abc 53a 60a 60a 53a Picloram 1.12 77a 50b - - 53a 57ab 47ao 63a Picloram 2.24 68a 60a 85a 70ab 50a 47ab 25ab 70a Tebuthiuron 0.37 77a 30d 65a 57abc 53a 53ab 53a 57a Tebuthiuron 1.12 55ab 15e - - 43a 53ab 43ab 70a Tebuthiuron 2.24 35b 30d 80ab 75a 60a~ 47ab 18b 50a £21211. Picloram 0.37 67a 30d 50d 50abc 40a 37bc 57a 60a Picloram 1.12 72a 40c - 47abc 47a 47ab 53a 57a Picloram 2.24 68a 37c 10f 63abc \7a 43ab 50ab 43a Tebuthiuron 0.37 67a 30d 53d 43bc 40a 37bc 50ab 70a Tebuthiuron 1.12 60a 25d - 43bc 50a 43ab 47ab 60a Tebuthiuron 2.24 57a 30d 40e 60abc 40a 23c 60a 40a Untreated ~ 61a 27d 37e 37c 37a 37bc 37ab 37a Means within each column followed by the same letter do not differ significantly at t the 5 percent level using Duncan's multiple-range test. * Evaluated 261 days after treatment. + Evaluated 210 days after treatment.