Control of Willow Baccharis and Spiny Aster with Pelleted Herbicides The Texas A&M University System ' The Texas Agricultural Experiment Station v Neville P. Clarke, Director, College Station,“ Texas‘ * wt Welder Wildlife Foundation Contribution No. 229. Metric Units - English Equivalents Metric English Unit ' Equivalent Centimeter 0.394 inch Hectare 2.47 acres Kilogram 2.205 pounds Kilogram per hectare 0.893 pounds per acre Kilometer 0.62 statute mile Kilometer per hour 0.62 miles per hour Liter 0.264 gallons Meter 3.28 feet Square meter (Degrees centigrade >< 1.8 + 32) 10.758 square feet Degrees iahrenheit Mention oi a trademark or a proprietary product does not consti- El tute a guarantee or warranty of the product by the Texas Ag- ricultural Experiment Station and does not imply its approval to the exclusion of other products that also may be suitable. V’ ‘ w: Contents Metric Units - English Equivalents . . . . . . . . . . . (inside front cover) Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Willow Baccharis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Spiny Aster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Willow Baccharis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Spiny Aster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Literature Cited . . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ll Appendix - Scientific Names of Plants Mentioned in Text . . . . . l2 Acknowledgments . . . . .r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Authors Mutz, I. L., assistant range scientist, The Texas Agricultural Ex- periment Station, Corpus Christi Scifres, C. I., professor. The Texas Agricultural Experiment Sta- tion (Department of Range Science) Mohr, W. C., range research technician, The Texas Agricultural Experiment Station (Department of Range Science) Drawe, D. L., assistant director, The Rob and Bessie Welder Wildlife Foundation, Sinton, Texas t’ I. “ Summary Willow baccharis is an invader of grasslands throughout Texas, and spiny aster is an increasing problem on lowlands of the Coastal Prairie. Conventional herbicide sprays cannot be used on many areas infested with willow baccharis because of the proximity of susceptible crops, and conventional sprays are not effective for control of spiny aster. Pelleted picloram or tebuthiuron, applied at l to 2 kilograms per hectare in the spring. effectively controlled willow baccharis. Both herbicides controlled willow baccharis, but the effects of tebuthiuron were not com- pletely manifested until the second growing season after applica- tion. Picloram pellets at l to 2 kilograms per hectare applied im- mediately after shredding spiny aster resulted in effective control. Neither component of the proposed spiny aster control system, shredding or herbicide application, was effective when used alone. Integration of the control methods resulted in increased production of native range forages on an Odem sandy clay loam soil in South Texas which supported residual forage plants at the time of treatment. However, artificial revegetation may be neces- sary when the system is used to renovate rangeland supporting dense stands of spiny aster with no seed source of native forage species. There were no differences between 5 or l0 percent pic- loram pellets for control of willow baccharis or spiny aster. The pelleted herbicides greatly reduce the drift potential associated with sprays, essentially eliminate the volatility hazards, and can be applied with ground or aerial equipment. O L’ Control of Willow Baccharis and Spiny Aster With Pelleted Herbicides During the last decade, willow baccharis (Bac- charis salicina), a Woody member of the Compo- sitae, has progressively become a management problem on native rangeland and tame pastures. Formerly restricted primarily to low, mesic areas, it aggressively invades the more productive grassland soils following disturbance, and is a persistent invader of abandoned fields (Hoffman, undated). Willow baccharis generally attains heights of 1 to 4 meters} It resembles the true willows’ in growth form, and is often referred to locally as "dryland willows," "seep willow," and "Roosevelt willow" (Figure 1). Willow baccharis is a management problem on grasslands in the southern half of Texas but also occurs in New Mexico, Colorado, and north to Kansas (Vines, 1960). It spreads by wind-blown achenes, and veg- etative regeneration is apparently limited to stem buds. Since willow baccharis seedlings and young plants are browsed by cattle, established plants are relatively rare in pastures with a history of grazing. Dense infestations invariably occur on grasslands which have been disturbed, mechani- cally or from a history of overgrazing, then com- pletely protected from grazing by domestic live- stock. Once established, the plants grow rapidly and may, within a few years, reduce desirable for- age production and retard improvement in range condition. Mature willow baccharis is only lightly ‘pf browsed by cattle; thus some control measure is generally needed to improve infested rangeland (Mutz et al., 1978b). Since willow baccharis resprouts from surviv- ing stem segments at or below ground line, top removal methods such as shredding and controlled burning result in only temporary control (Scifres and Haas, 1974). However, no research on the use of grazing following shredding or burning treat- Q_______ \y 4T0 convert metric to English unit, see table inside front cover. ‘Scientific names of all plants and animals mentioned in text are given in Appendix. ments for sprout control has been conducted. Since the species is shallow rooted, grubbing is effective for control where plant densities are low (< 250 per hectare). Broadcast sprays of 2,4,5-T [(2,4,5-tri- chlorophenoxy) acetic acid] at l kilogram of active ingredient per hectare or less result in only partial control. However, the low volatile esters of 2,4-D [(2,4-dich1orophenoxy) acetic acid] at 1.68 to 2.24 kilograms of active ingredient per hectare effec- tively control willow baccharis. Broadcast applica- tions of 1:1 combination of 2,4,5-T + picloram (4- amino-3,5,6-trichloropicolinic acid) at 1.12 kilo- grams of active ingredients per hectare total her- bicide have shown promise for willow baccharis control (Scifres and Haas, 1974). Another troublesome composite on range sites with high production potential in South Texas is spiny aster (Aster spinosus). Also known as "Mexi- can devi1weed" or "wolfweed," spiny aster is a warm-season perennial which may exceed 1 meter in height. It commonly occurs in ditches, swales, stream bottoms, and other low mesic areas (Iones, 1975) and will invade upland sites where soils have a high clay content and a high water-holding capacity (Mayeux, 1977). Infestations of spiny aster often essentially exclude desirable vegetation (Figure 2). Spiny aster occurs in the southern and western half of Texas with the northeast range extending to Brazos County (Correll and Johnston, 1970) and in New Mexico, Arizona, and Utah. The Coastal Prairie supports the most extensive infestations of spiny aster in Texas. Most sites supporting only spiny aster have high potential for range forage production (Mutz, 1976; Mutz et al., 1978a). Spiny aster initiates vegetative growth from a well-developed rhizome system during early spring. Small leaves are present for a brief period during the spring while the young stems are succu- lent. The leaves drop off after 2 or 3 weeks, and the stem becomes photosynthetically active (Mayeux, 1977). Since only a portion of the mature spiny aster 3 bicides under certain conditions, potential drift hazards have restricted treatment of many infested areas. The potential of spray drift damage to sus \ ceptible crops and stringent-timing requirements ' relative to plant phenology for effective applica- tion of herbicide sprays have provided the im- stems overwinter to continue growth and develop- ment the following season, mature stands are often characterized by an abundance of dead stems. A mature spiny aster community may sup- port more than 100 stems per square meter. White-tailed deer and feral hogs apparently utilize spiny aster communities for cover. Although white-tailed deer will occasionally eat succulent stems and leaves during the early spring (Cham- rad and Box, 1968), the overall extent of utilization is apparently low. Therefore, range improvement following spiny aster control is generally consid- ered to be more practical than leaving the stands for wildlife cover. Effective control of undisturbed spiny aster has not been achieved with foliar herbicides. Di- camba (3,6-dichloro-o-anisic acid) and 2,4-D at 1.12 or 2.24 kilograms active ingredients per hectare alone or the same rates in combinations applied as a foliar spray in the fall failed to control mature spiny aster (Mayeux and Scifres, 1975). However, shredding as a pretreatment to stimulate new growth, followed by a foliar spray of the potassium salt of picloram at 1.12 kilograms of active ingre- dients per hectare completely controlled spiny as- ter. Although willow baccharis and spiny aster may be controlled with foliar sprays of some her- petus for evaluating dry herbicide formulations for range improvement (Scifres et al., 1978). Pelleted herbicides greatly reduce drift potential, essen- tially eliminate the hazard of volatility and extend the period for effective herbicide application. Pelleted picloram effectively controls trouble- some range species such as redberry juniper (Sci- fres, 1972), lotebush (Scifres and Kothmann, 1976), Macartney rose (Scifres, 1975a). and Texas per- simmon (Scifres, 1975b). These species are difficult or impossible to control with conventional broad- cast spra s. A relatively new herbicide, tebuthi- uron (N- 5-(1,-dimethylethyl)-LSA-thiadiazol-Zyq -N,N' - dimethylurea) appears promising for contro of whitebrush, spiny hackberry, Berlandier wolfberry, and other woody plants not effectively controlled by other herbicides and formulations (Scifres et al., 1978). The objective of this research was to evaluate the effectiveness of pelleted piclo- ram and tebuthiuron for control of willow bac- charis and spiny aster. MATERIALS AND METHODS Willow Baccharis The first experiment was installed near Col- 7; ._ a‘ lege Station on March 24, 1976. A typical East Texas mixed-brush infestation had been removed from the area by tree-dozing in 1964. The area sup- ported a dense stand (> 1,200 plants per hectare) of willow baccharis, 2.5 to 3 meters tall, when the experiment was initiated. Primary grasses were ' a '9 Figure 2. Spiny aster infestations usually are so dense that mos. .1 desirable range forages are excluded. Figure 1. Willow baccharis, a management problem following disturbance of rangeland and on abandoned fields, resembles thetrue willows in growth form. brownseed paspalum, broomsedge bluestem, silver bluestem, and scattered clones of little blue- stem. The soil was a Tabor fine sandy loam, a member of the fine, montmorillonitic, thermic fam- ily of Udertic Paleristalfs. Pelleted picloram was applied broadcast to 12.5 by 40.5- meter plots sepa- rated by 2-meter-wide buffer strips. Herbicide was applied in swaths 6.25 meters wide with a tractor-mounted broadcast spreader (Figure 3). The spreader was calibrated with pellets not contain- ing active herbicide prior to actual plot applica- tion, but final application rates were based on the "weight difference" method relative to exact area treated. Therefore, rates applied varied somewhat among formulations. Treatments, duplicated in randomized complete block design, included pic- loram pellets containing 5 percent active ingre- dient (approximately 2.4 millimeters in diameter) applied to 0.5 and 1.5 kilograms of active ingre- dients per hectare, and pellets containing l0 percent active ingredients (approximately 3.2 mil- limeters in diameter) applied at 0.8 and 1.5 kilo- grams per hectare. At 7 and 14 months after appli- cation, percentage canopy reduction of each plant was recorded within a 2-meter-wide transect down the center of each plot. The number of willow bac- charis completely defoliated and showing no signs of life was also recorded. At 17 months after appli- cation, the number of live seedlings was recorded in ten 0.25-square-meter quadrats equidistantly spaced along a diagonal across each plot. Three composite soil samples were recovered from 0 to 8, 8 to 15, 15 to 30, and 30 to 60 centimeters deep. Organic matter content by acid digestion and titration, pH on a 1:4 soilzwater slurry, and tex- tural components by the hydrometer method were determined on triplicate subsamples from each depth. A second experiment, located within 100 meters of the first, was installed on May 25, 1976, in a field abandoned from crop production in 1972. The area supported a dense, uniform stand of willow baccharis about 2.5 meters tall. Herbicides applied at 1.12 and 2.24 kilograms of active ingre- dient per hectare with a hand spreader to 23.4- by 23.4-meter plots included picloram as the 5- or 10- percent formulations, and tebuthiuron as a 20- percent formulation. Tebuthiuron pellets were ex- truded and about 3.2 millimeters in diameter. Each treatment was triplicated in a randomized com- plete block design. Plots were separated by 2-meter-wide buffer strips. At 2, 7, and 11 months after herbicide application, percentage canopy re- duction of willow baccharis and number of plants completely defoliated were recorded on each plot. The study areas near College Station were not grazed. On March 29, 1977, an experiment was in- stalled near Agua Dulce, Texas on the Coastal Prairie. The soil was a Clareville clay loam, a member of the fine, montmorillonitic, hyperther- mic family of the Pachic Arguistalls. The study area had been abandoned from row-crop produc- tion in 1972 and sprigged with coastal Bermuda- grass in 1973. The study area supported a well- established stand of coastal Bermudagrass limited only by the dense (>3,000 plants per hectare) infes- tation of willow baccharis which averaged 2.5 meters tall. Picloram pellets as the 5-percent for- mulation were applied with a tractor-mounted broadcast seeder/spreader at 1.34 and 2.89 kilo- grams of active ingredients per hectare, and at 1.17 and 2.37 kilograms of active ingredients per hec- tare as the 10-percent formulation (Figure 4). Tebu- thiuron pellets were applied at 1 and 4.2 kilograms active ingredient per hectare. Plot size was 32.7 by 65.5 meters, and each treatment was duplicated in a randomized complete block design. The study area was not grazed for 5 months after herbicide application. Soils were characterized as described for the study near College Station. Figure 4. Excellent control of willow baccharis was achieved within 1 year following application of 1.12 kilograms per hec- tare of 5 or 10 percent active ingredient picloram pellets near Agua Dulce, Texas. . 1F igure 3. A tractor mounted broadcast seeder/spreader was '\~ used to apply pelleted herbicides to willow baccharis and spiny aster infested areas. l" "£4 At 4 and 14 months after treatment, percentage canopy reduction of each willow baccharis plant. and the number of plants completely defoliated were recorded within a 2-meter-wide belt down the center of each plot. Spiny Aster On Iune 1, 1976, an experiment was installed on the Rob and Bessie Welder Wildlife Foundation approximately l5 kilometers northeast of Sinton, in the Gulf Prairie and Marshes (Gould, 1975). Aver- age annual precipitation is approximately 92 cen- timeters. Soil within the study area is an Odem fine sandy loam, a member of the fine-loamy, mixed, hyperthermic family of the Cumulic Hap- lustolls. The study area was located in a spiny aster-longtom plant community (Drawe et al., 1978) within 100 meters of the Aransas River which periodically inundates the area. Picloram pellets (5 or 10 percent active ingredient) at 0.56 and 1.12 kilograms of active ingredients per hectare, and tebuthiuron pellets (20 percent active ingredient) at 1.12 kilograms of active ingredient per hectare, were applied to plots which had been shredded to a 10-centimeter height on May 15, 1976, and to un- disturbed spiny aster. The pelleted herbicides were applied with the tractor-mounted broadcast seeder/spreader to plots 12.2 by 45.7 meters. The experiment was designed as a randomized com- plete block arranged as a split-plot with two replications of each treatment. Pretreatment (shredding) constituted the main block effect and herbicide treatments were applied to subplots, 12.2 by 22.8 meters. At 3 and 12 months after herbicide application, number of live spiny aster stems and average stem height were recorded within ten 0.25-square-meter sample areas equally spaced down the center of each plot. A second study was installed in 1977 within 20 meters of the 1976 experiment. The spiny aster was shredded on March 28, 1977. Five and l0 percent active ingredient picloram pellets were applied to 24- by 45.7-meter plots on March 29. Experimental design, method of herbicide application, and soil series were identical to the first experiment. On Iuly 25, 1977, and Iune 23, 1978, number of live spiny aster stems was recorded, and forage stand- ing crop was determined within ten 0.25-square- meter quadrats equidistantly spaced along a diagonal line across each plot. Cattle had been grazing within the study area for approximately 6 weeks prior to the evaluation on Iune 23, 1978 (Fig- ure 5). Percent overall utilization by cattle within each treated plot was estimated by two workers. Two additional experiments were installed on March 22, 1978, near Refugio, Texas. One experi- mental area was located on an upland site sup- porting a sparse stand of spiny aster (<2,000 live stems per hectare) l0 to 20 centimeters tall. Other vegetation present within the study area included Hall's panicum, little bluestem, Texas winter- grass, pink eveningprimrose, and narrowleaf sumpweed. The spiny aster was not tall enough to justify shredding. Therefore, picloram pellets were. y applied without pretreatment to the spiny aster at 1.2 kilograms of active ingredient per hectare as the 5-percent or 10-percent formulation to 30.5 by 61-meter plots. Pellets were applied with a tractor-mounted broadcast seeder/spreader to trip- licate plots arranged in a randomized complete block design. The other experimental site near Refugio sup- ported a dense stand of spiny aster, 2 meters tall (>20,000'live stems per hectare) and was located on bottomland virtually devoid of other vegetation. Picloram as the 5- or 10-percent pellets was applied at 1.2 kilograms of active ingredient per hectare to triplicate, 30.5 by 61-meter plots. Half of each plot was shredded to a 10-centimeter stubble .. . .\,-‘_ why . _s _' l "°' k l i >' '- . - "T. 3 . I». .- .,¢ _- 1 *.._..»v\ . . <- Figure 5. Shredding spiny aster on the near Sinton and immediately applying 1.12 kilogram per hec- tare of picloram ( 5- or 10-percent formulation) on March 29, I977 1 l (a) resulted in tenfold increase in forage standing crop after 85 days (b). Welder Wildlife Refuge A 1'" ‘ a1 height immediately prior to herbicide application. Treatment effects were evaluated, as previously escribed, at 4 months after herbicide application. The soil of both sites was a Victoria clay, a member Y of the fine, montmorillonitic, hyperthermic family of the Udic Pellusterts. Data from each experiment were subjected to analysis of variance, and Duncan's New Multiple Range Test was used to separate means at the 95- percent confidence level. RESULTS AND DISCUSSION Willow Baccharis The time required for manifestation of phytotoxicity of soil-applied herbicides is a func- tion of root-uptake and amount of rainfall, soil characteristics, and the target species involved. Willow baccharis on Tabor sandy loam (Table 1) exhibited symptoms of picloram phytotoxicity, epinasty of young stem tips and leaf chlorosis, within 2 weeks after the first significant rainfall (1 centimeter or more). Average defoliation of willow baccharis was 26 percent, and 5 percent of the plants were completely defoliated and showing no signs of life at 7 months after application of the 5-percent formulation of picloram pellets at 0.5 kilogram per hectare (Table 2). The 10-percent for- mulation applied at 0.8 kilograms per hectare re- duced average live canopy by 91 percent, and 69 percent of the plants were completely defoliated. The influence of formulation was confounded by rate in this study, particularly since the threshold rate for maximum response of willow baccharis is relatively low, apparently between 0.5 and 0.8 kilogram of picloram per hectare (Table 2). Canopy reduction was 99 to 100 percent, and 96 to 100 percent of the plants were completely de- foliated, regardless of picloram formulation, at 7 months after application of 1.5 kilogram of active ingredients per hectare. The 1.5 kilogram of active Table 1. Organic matter content, pH, and textural components of two soils treated with pelleted picloram and tebuthiuron for willow baccharis control. cgrngirefirc Textural components (%) pH Sand Silt Clay Tabor sandy loam (College Station) 0-8 1.55 5.6 50 39 1 1 8-15 1.07 5.5 48 37 15 15-30 0.87 5. 1 36 37 27 30- 60 0. 92 6. 1 28 37 35 Clareville clay loam (Agua Dulce) o-s 2.12 s7 s7 17 2s ($15 1.ss s.a ss 1v 2s \ 1s-s0 1.75 7.0 s4 1s so so-so 1.22 1.0 s1 1s as ingredient per hectare rate of either formulation completely controlled the willow baccharis by 14 months after picloram pellet application (Table 2). Control at the 0.5- and 0.8-kilogram-of-active-in- gredient-per-hectare rate was not satisfactory. Willow baccharis seedlings had established in treated plots by l7 months after herbicide appli- cation. Plots treated with l.5 kilograms per hectare of picloram supported significantly fewer willow baccharis seedlings than did untreated plots (Ta- ble 3). The lower number of seedlings in treated plots was attributed to residual activity of pic- loram. At rates of 1.12 kilograms per hectare or higher, picloram residues following application of pellets can be expected to persist in the soil into the next growing season (Bovey and Scifres, 1971). This persistence is a positive attribute when deep- rooted perennial plants and invading seedlings are the target of control efforts. In August, 4 months after evaluation of reinva- sion of the experimental plots with willow bac- charis seedlings, the study site near College Sta- tion was grazed with heifers at four animals per hectare for 14 days. Willow baccharis seedlings, 15 _ Table 2. Average canopy reduction (%) of willow baccharis and percentage of the population completely defoliated and not re- sprouting after application of picloram pellets on March 24 and 25, 1976, near College Station. Texas. Months after treatment“ Treatment 7 14 Active Rate Canopy Plant Canopy Plant ingredient (kg/ha) reduction kill reduction kill (%) (%) (%) (%) (%) Untreated 0 0 a 0 a 0 a 0 a 5 0.5 26 b 5 a 46 b 17 b l0 0.8 91 c 69 b 75 c 73 c l0 1.5 100 c 100 c 100 d 100 d “Means within a column followed by the same letter are not significantly different at the 0.5-level according to the Student-Newman-Keul's Test. Table 3. Average density of willow baccharis seedlings on Au- gust 29, 1977 after treatment of mature stands with pelleted picloram on March 24 ar1d 25, 1976, near College Station, Texas. Picloram treatment Active Rate Seedlings/mz “ ingredient (kg/ha) (%) 0 7.2 c 5 0.5 4.1 b 5 1.5 0.7 a 10 0.8 7.8 C 10 1.5 0.2 a “Means within a column followed by the same letter are not significantly different at the 95% level according to Duncan's New Multiple Range Test. l" w; to 20 centimeters tall, were counted immediately before and again after the grazing period. Cattle removed essentially all willow baccharis seed- lings, regardless of original picloram treatment (data not shown). Integration of grazing manage- ment with picloram pellet treatment, then, holds promise for permanent control of willow baccharis. The 5-percent picloram formulation tended to be more effective than the 10-percent formulation for controlling willow baccharis at 2 months after installation of the second experiment near College Station (Table 4). There was no difference in willow baccharis control between the picloram formula- tions within a rate or between rates at 7 and ll months after application. At 7 months after appli- cation, tebuthiuron at 1.12 kilograms per hectare reduced the willow baccharis canopy by 83 per- cent, which was significantly less than the amount of canopy reduction by 5 or l0 percent formulation of picloram at 1.12 kilograms per hectare and tebuthiuron at 2.24 kilograms per hectare (Table 4). At ll months after treatment, the 1.12 kilogram per hectare rate reduced the canopies by 96 to 98 percent, and complete control was achieved by the high application rate, regardless of formulation. Willow baccharis tended to respond to tebuthiuron somewhat more slowly than to picloram pellets, Table 4. Average canopy reduction (%) of willow baccharis after application of various rates of picloram and tebuthiuron pellets on May 25, 1976, near College Station, Texas. Active Herbicide ingredient Rate Months after treatment“ (%) (kgl ha) 2 7 l l None 0 7 a 7 a 7 a Picloram 5 1.12 96 d 96 c 98 b Picloram 5 2. 24 98 d 100 c 100 b Picloram l0 l. 12 85 bc 95 c 96 b Picloram l0 2. 24 89 c 95 c 100 b Tebuthiuron 20 1.12 78 b 83 b 99 b Tebuthiuron 20 2.24 83 bc 94 c 98 b “Means within a column followed by the same letter are not significantly different at the 0.5-level according to Student- Newman-KeuYs Test. but there was no difference in level of control be- tween herbicides, regardless of application rate. at ll months after application (Table 4 y Tebuthiuron has shown promise for controlling several other woody speciesDon rangeland (Scifres et al., 1978). There was no difference in canopy reduction of! willow baccharis at 4 or l4 months after applica- tion of 5- or l0-percent formulations of picloram at rates ranging from l.l to 2.9 kilograms per hectare near Agua Dulce (Table 5). The canopy was re- duced from 97 to 99 percent at 4 months after appli- cation, and was essentially eliminated by 14 months after application of picloram pellets. After 4 months approximately one-half of the willow baccharis population was killed by the lower rates of 5- or 10-percent formulation of picloram pellets. The 5-percent formulation at 2.9 kilograms of ac- tive ingredient per hectare killed approximately 91 percent of the willow baccharis after 4 months. Fourteen months following application there was no difference in the percentage of the willow bac- charis population killed by the various rates of the two formulations of picloram. Tebuthiuron at l and 4.2 kilograms per hectare reduced willow bac- charis canopies by l7 and 57 percent, respectively, at 4 months following application. However, the tebuthiuron treatments eliminated willow bac- charis canopies by 14 months after herbicide ap- plication. Tebuthiuron applied at 1 kilogram per hectare had not killed any willow baccharis plants after 4 months. However, approximately 24 percent of the plants were killed by 4.2 kilograms of her- bicide per hectare (Table 5). After 14 months, l kilogram of active ingredient per hectare of tebuthiuron killed 43 percent of the willow bac- charis plants while 4.2 kilograms of active ingre- dients per hectare killed 92 percent of the plants. Results of these experiments indicate that willow baccharis can be effectively controlled by applications of picloram pellets at rates of at least l kilogram per hectare. Tebuthiuron appeared to control willow baccharis at 1.12 kilograms of active Table 5. Average canopy reduction (%) and percentage of population of willow baccharis completely defoliated and showing no signs of life at 4 and l4 months after application of various rates of pelleted picloram and tebuthiuron on March 29. 1977, near Agua Dulce, Texas. 4 months 14 months Active Canopy Dead Canopy Dead ingredient Rate reduction“ plants“ reduction plants Herbicide (%) (kg/ha) (%) (%) (%) (%) None A. 0 7 a 0 a 0 a 0 a Picloram 5 1.3 99 d 55 c 98 b 87 c Picloram 5 2.9 99 d 9l d 100 b 99 d Picloram l0 l.l 97 d 47 c 100 b 97 d Picloram 10 2.4 99 d 70 c 100 b 99 d Tebuthiuron 20 1.0 17 b 0 a 100 b 43 b Tebuthiuron 20 4.2 57 c 24 b 100 b 92 cd ( ; “Means within a column followed by the same letter are not significantly different at the 95% level according to Duncan's New Multiple Range Test. 8 ingredients per hectare on a sandy loam soil, but higher rates were necessary on a clay loam soil. Higher rates of either herbicide might be advan- ' c q tageous on seriously deteriorated rangeland to re- tard reinvasion of seedlings until a grass cover is established. Thereafter, establishment of willow baccharis seedlings may be prevented by grazing management. These pelleted herbicide formula- tions offer the resource manager considerable flex- ibility in that both aerial and ground applications are feasible, depending on extent of willow bac- charis infestation. a Spiny Aster Undisturbed spiny aster exhibited slight symptoms of picloram phytotoxicity at 3 to 4 weeks after the first significant rainfall following her- bicide application to an Odem fine sandy loam on the Welder Wildlife Refuge. By 95 days after her- bicide treatment, undisturbed spiny aster was not affected by 0.56 or 1.12 kilograms per hectare of picloram, regardless of formulation, or by 1.12 kilograms per hectare of tebuthiuron (Table 6). Shredding reduced the original standing crop to a 10-centimeter stubble, but by 95 days after top re- moval, spiny aster had replaced approximately 30 percent of its original top growth when no her- bicide was applied. Shredding followed by appli- cations of 0.56 or 1.12 kilograms of active ingre- dients per hectare of picloram (5- or 10-percent formulation) reduced the original stem density from 69 to 94 percent after 95 days (Table 6). Pic- loram at 0.56 kilogram of active ingredients per hectare was generally less effective in reducing live stem densities of spiny aster than was 1.12 kilograms of active ingredients per hectare. How- ever, surviving stems did not make significant additional growth until 1 year after herbicide ap- plication. One year following application of pic- loram pellets, the lower rate was less effective than the higher rate in reducing the height of sur- viving spiny aster stems (data not shown). At 95 days after application, tebuthiuron at 1.12 kilo- grams per hectare reduced original live stem den- sities of spiny aster by 49 percent (Table 6). This reduction was not considered adequate for improv- ing spiny aster-infested communities based on forage response. Therefore, only picloram at 1.12 kilograms per hectare was evaluated in sub- sequent studies. Spiny aster growth was significantly reduced by 85 days after application of the 5- or 10-percent picloram pellets at 1.12 kilograms per hectare in the second experiment on the Welder Wildlife Ref- uge (Table 7). Only trace amounts (<0.l stern per 0.25 square meter yielding less than 5 kilograms per hectare) of spiny aster occurred on shredded plots which were treated with picloram. At _the same time, plots that had been shredded and then treated with 5- or 10-percent picloram pellets sup- ported 4,410 and 4,580 kilograms per hectare, re- spectively, of oven-dry standing crop. Untreated plots supported only 450 kilograms per hectare of grasses. Spiny aster standing crop was 8,210 kilo- grams per hectare at 85 days after initiation of the second experiment on the Welder Wildlife Refuge (Table 7). Shredded plots treated with 1.12 kilo- grams per hectare of picloram supported only trace amounts of spiny aster, reflecting the value of shredding as a pre-treatment to herbicide applica- tion. Shredding without picloram allowed foliar cover of grasses to increase from 6 to 45 percent during the year of treatment. However, unless shredded areas were treated with herbicide, spiny aster regrowth markedly reduced grass standing crop by the following growing season. Based on a 25-percent utilization of forage by cattle and a daily requirement of 12 kilograms dry matter per day to support an animal unit (450 kilo- gram cow with calf), plots shredded and treated with 1.12 kilograms per hectare of picloram pellets on the Welder Refuge offered about 93 animal-unit days grazing per hectare (about 3.1 animal-unit months). A projected stocking rate for this site was about 4 hectares-(l0 acres) per animal unit year- long, based on forage recovery within 90 days after treatment. In comparison, the untreated site would Table 6. Live stem reduction (%) and mean height (m) of spiny aster stems at 95 days after herbicide application to plots shredded on May 15, 1976, and to undisturbed plots treated on Iune l, 1976, with several rates of picloram and tebuthiuron pellets on Welder Wildlife Refuge near Sinton, Texas. ? Undisturbed“ Shredded Live stem Live stem Formulation Rate reduction reductionb H: Herbicide (% a.i.) (kg/ha) (%) (%) (m) None 0 0 0 0 a 0.3 Picloram ' 5 0.56 0 83 d 0.1 Picloram 5 1.12 0 94 d 0.1 Picloram l0 0.56 0 69 c 0.1 Picloram 10 1.12 0 85 d 0.1 ‘Tebuthiuron 20 1.12 0 49 b 0.2 \ . ‘ “Undisturbed spiny aster stems average 1 meter tall. bMeans followed by the same letter are not significantly different at the 95% level according to Duncan's New Multiple Range Test. T; v a‘ support 1 animal unit per 39 hectares. Spiny aster control combined with good grazing management and average rainfall should easily provide grazing for 1 animal unit per 6 hectares yearlong on sites similar to those on the Welder Wildlife Refuge study area. At 15 months after application, standing crop of grasses on shredded plots treated with 5- or 10- percent formulation of picloram pellets was 2410 and 2290 kilograms per hectare, respectively, of which 55 and 60 percent, respectively, was utilized by cattle during the 90-day grazing period preced- ing evaluation (Table 8). Unshredded plots treated with 1.12 kilograms per hectare of pelleted pic- loram supported 370 to 490 kilograms per hectare of grass standing crop of which only l0 percent was utilized by livestock. Shredded plots which were not treated with pelleted picloram supported 531 kilograms per hectare of standing crop of which 20 percent was utilized. Untreated plots supported only 130 kilograms per hectare of standing crop of which 12 percent was utilized by cattle (Table 8). Spiny aster responses to applications of pic- loram pellets at 1.12 kilograms per hectare on the Victoria clay sites near Refugio were similar to those on the Odem fine sandy loam site near Sin- ton, regardless of shredding treatment. Four months following application of the pellets during which time 15 centimeters of precipitation were re“ \ 1. ceived, the untreated upland site supported 27 live, spiny aster stems persquare meter while plots treated with 5- or 10-percent picloram pellets con- tained three and one live spiny aster stems per square meter, respectively (Table 9). On the low- Table 9. Spiny aster densities (plants per square meter) at 4 months after application of 5- or 10-percent picloram pellets at 1.2 kilograms of active ingredients per hectare on March 27, 1978, to undisturbed spiny aster on an upland site, and to shredded and undisturbed spiny aster on a lowland site near Refugio, Texas.“ Spiny aster density Picloram (plants/mz) formulation Upland site Lowland site (%) Not shredded Shredded Not shredded None 27 b 76 c 75 c 5 3 a 5 a 41 b 10 1_ a 4 a 34 b “Means within a column followed by the same letter-are not significantly different at the 95% level according to Duncan's New Multiple Range Test. Table 7. Standing crop of grasses and spiny aster (kilograms per hectare), foliar cover of grasses, and spiny aster densities at 85 days after application of 1.12 kilograms per hectare of 5- or 10-percent picloram pellets on March 29, 1977, to shredded and undisturbed spiny aster on the Welder Wildlife Refuge near Sinton, Texas.“ Treatment Standing crop (kg/ha) Grass Spiny foliar aster Herbicide Formulation Grasses Spiny Aster cover density (%) (%) (plants/mz) Not shredded None 450 a 8,210 e 6 a 44 d Picloram 5 1,070 b 3,470 c 30 b 28 c Picloram 10 1,280 b 4,915 d 45 b ll b Shredded None 1,750 c 1.420 b 45 b 56 d Picloram 5 4,410 d Tb a 68 c T a Picloram 10 4,580 d T a 69 c y T a “Means within a column followed by the same letter are not significantly different at the 95% level according to Duncan's New Multiple Range Test. bTrace — a few scattered spiny aster plants (fewer than 0.04 per square meter) yielding less than 5 kilograms per hectare. Table 8. Standing crop of grasses (kilograms per hectare) and percentage utilization (%) at 15 months after application of 1.12 kilograms per hectare of the 5- or 10-percent formulation of pelleted picloram to shredded and undisturbed spiny aster on the Welder Wildlife Refuge near Sinton, Texas, on March 29, 1977.“ Treatment Herbicide Formulation Standing crop (kg/ha) Utilization (%) (%) Shredded Not shredded Shredded Not shredded Control - 531 c 130 a 20- 0 12 a Picloram 5 2,410 d 370 b 55 b 10 a Picloram 1o 2,290 d 490 ¢ 60 b 10 a “Means within a column followed by the same letter are not significantly different at the 95% level according to Duncan's New Multiple Range Test. l0 4 land site, shredded plots supported 4 or 5 live spiny aster stems per square meter, while un- ifixeated plots supported 76 live spiny aster stems 1:" ‘is; er square meter. Plots treated only with herbicide supported 34 and 41 live spiny aster stems per square meter. Since the lowland site had been heavily in- fested with spiny aster for several years, other vegetation did not become established following spiny aster control. Revegetation with adapted grass species will be necessary to expedite the cost return of shredding and herbicide treatment on such sites. LITERATURE CITED Bovey, R. W., and C. I. Scifres. 1971. Residual characteristics of picloram in grassland ecosystems. Texas Agr. Exp. Sta. Bull. 1111.24 pp. Chamrad, A. D., and T. W. Box. 1968. Food habits of white- tailed deer in South Texas. I. Range Manage. 21:158-164. Correll, D., and M. Johnston. 1970. Manual of the vascular plants of Texas. Texas Research Foundation, Renner. 1881 PP- Drawe, D. L., A. D. Chamrad, and T. W. Box. 1978. Plant com- munities of the Welder Wildlife Refuge. Welder Wildlife Foundation Contrib. No. 5, Series B, Revised. Sinton, TX. 38 PP- Gould, F. W. 1975. Texas Plants — A checklist and ecological summary. Texas Agr. Exp. Sta. Misc. Pub. 585. 121 pp. Hoffman, G. O. (Undated) Control of baccharis. Texas Agr. Ext. Ser. L-753. 1 p. Iones, F. B. 1975. Flora of the Texas Coastal Bend. Mission Press, Corpus Christi, TX. 262 pp. Mayeux, H. S. Ir., and C. I. Scifres. 1975. Control of spiny aster. Proc. South. Weed Sci. Soc. (Abstr.) 29:257. Mayeux, H. S. 1977. Ecology and herbicidal control of selected perennial range weeds of South Texas. Ph.D. Diss., Dep. of Range Science, Texas A8zM Univ., College Station. 247 pp. Mutz, I. L. 1976. Spiny aster: Growth and development, ecology, and promising techniques for manipulation. Rob and Bess- ie Welder Wildl. Found., Sinton, Texas, and Texas Agr. Exp. Sta. (mimeo). 26 pp. Mutz, I. L., C. I. Scifres, and D. L. Drawe. 1978a. Control of spiny aster with pelleted herbicides. Proc. South. Weed Sci. Soc. 31:189. Mutz, I. L., C. I. Scifres, and W. C. Mohr. 1978b. Willow bac- charis and its control. Proc. Ann’. Mtg. Soc. Range Manage. 31:52. Scifres, C. I. 1972. Redberry juniper control with soil-applied herbicides. I. Range Manage. 25:308-310. Scifres, C. I. 1975a. Systems for improving Macartney rose-in- fested coastal prairie rangeland. Texas Agr. Exp. Sta. Misc. Pub. 1225. 12 pp. Scifres, C. I. 1975b. Texas persimmon distribution and control with individual plant treatments. Texas Agr. Exp. Sta. Bull. 1157. 12 pp. Scifres, C. I. and R. H. Haas. 1974. Vegetation changes in a post oak savannah following woody plant control. Texas Agr. Exp. Sta. Misc. Pub. 1136. 12 pp. Scifres, C. I., I. L." Mutz, and W. T. Hamilton. 1978. Control of mixed brush with tebuthiuron. I. Range Manage. 32:(March) (In Press). Scifres, C. I., and M. M. Kothmann. 1976. Site relations, re- it growth characteristics and control of lotebush with her- bicides. I. Range Manage. 29:154-156. Vines, R. A. 1960. Trees, shrubs and woody vines of the South- west. Univ. Texas Press, Austin. 1104 pp. 11 "L fi ._ ‘4 Appendix Scientific Names of Plants and Animals Mentioned in Text Common Name Redberry juniper Lotebush Macartney rose Texas persimmon Whitebrush Spiny hackberry Berlandier wolfberry Brownseed paspalum Broomsedge bluestem Silver bluestem Little bluestem Coastal Bermudagrass Hall's panicum Texas wintergrass Pink eveningprimrose Narrowleaf sumpweed Feral hogs White-tailed deer Plants Latin Name Iuniperus pinchoti Ziziphus obtusifolia Rosa bracteata Diospyros texana Aloysia Iycioides CeItis paIhda Lycium berlandieri var. berlandieri Paspalum plicatulum Andropogon virginicus Bothriochloa saccharoides Schizachyrium scoparium var. frequens Cynodon dactylon Panicum hallii Stipa Ieucotricha Oenothera speciosa var. speciosa Iva angustifolia Animals Sus scrofa Odocoileus virginianus ACKNOWLEDGMENTS The authors thank I. Wright, Agua Dulce; Torn O'Connor, Ir., Victoria; and H. M. Fagan, Refugio, for providing assistance and land use for this re- search project. Dow Chemical Company and Lilly Research Laboratories provided the herbicides for these studies. 12 [Blank Page in Original Bulletin] 7*‘ "s; All programs and information of the Texas Agricultural Experiment Station are available to everyone without regard to race, color, religion, sex, or national origi The Texas Agricultural Experiment Station, Neville P. Clarke, Director, College Station, Texas 2.2 5M--3-79