HERBICIDES TO AID ESTABLISHMENT OF FOURWING SALTBUSH Joseph L. Petersen Darrell N. Ueckert Matthew W. Wagner ABSTRACT of this study was to identify herbicides effective for selec­ tive control of competing vegetation in fourwing saltbush Failures in attempts to establish fourwing saltbush plantings. (Atriplex canescens) are often attributed to interference from weeds. Field experiments were conducted in western Texas to evaluate preemergence and postemergence appli­ MATERIALS AND METHODS cations of selected herbicides for we~d control in fourwing The study was conducted on an Angelo clay loam saltbush plantings. Sprays ofmetolachlor at 2.0 kg a.i.lha (fine, mixed, thermic Torrertic Calciustolls) at the Texas and alachlor at 2.5 kg/ha appeared promising as preemer­ A&M University Agricultural Research and Extension gence treatments. Acifluorfen at 0.56 kglha and clopyralid Center, 8 km northwest of San Angelo in the southern at 0.28 kg/ha effectively controlled broadleafed weeds, and Rolling Plains resource area. Soil pH was 7.8 and organic fluazifop-P at 0.21 kg/ha effectively controlled grasses matter content was 1.2 percent.. Elevation is 580 m and while causing no or only slight injury to fourwing saltbush mean annual precipitation is 47 em. The most predictable plants that were 1 month to 2 years old. Postemergence and abundant periods of rainfall are April-June and herbicides appear more practical than preemergence herbi­ September-October. cides in arid and semiarid areas where fourwing saltbush is utilized. Preemergence Herbicide Experiments INTRODUCTION Selected preemergence herbicide treatments were evaluated in three experiments. Seedbeds were disked Fourwing saltbush (Atriplex canescens) is used exten­ twice and packed before planting. About 800 dewinged sively for rangeland seeding because of its wide range fourwing saltbush seeds (4 g) from a commercial source of adaptation to edaphic and climatic conditions and its (harvested in western Texas) were hand planted 1.3 em potential to produce nutritious forage for livestock and deep in each of two 120-cm rows in 2- by 2-m plots sepa­ wildlife, particularly during winter (Plummer and others rated by 1.2-m borders. Germination of the seed on moist 1966; Petersen and others 1987). However, success in blotter paper in a controlled environment was 22 percent. establishing the shrub by seeding or transplanting Herbicide treatments included trifluralin [2,6-dinitro­ seedlings has been highly variable. Failures have been N ,N-dipropyl-4-(trifluoromethyl)benzenamine] at 0.8 kg attributed to poor seedbed preparation, poor seed quality, a.i .lha, oryzalin [4-( di propyl amino)-3,5-dini trobenzene­ inadequate soil moisture, grazing, and excessive competi­ sulfonamide] at 1.1 kg/ha, ethalfluralin [N-ethyl-N-(2- tion from associated plants (Springfield 1970; Nord and methyl-2-propenyl)-2, 6-dinitro-4-( trifl uoromethyl)­ others 1971; Aldon 1972; Petersen and others 1986). benzenamine] at 1.9 kg/ha, metolachlor [2-chloro-N-(2- Plant competition is most often the primary factor ethyl-6-methyl phenyl)-N-(2-methoxy-1-methylethyl)­ limiting establishment offourwing saltbush plantings acetamide] at 2.0 kg/ha, and alachlor [2-chloro-N-(2,6- (Giunta and others 1975; VanEpps and McKell 1977, diethylphenyl)-N-(methoxymethyl)acetamide] at 1983; Geist and Edgerton 1984; Petersen and others 2.8 kg/ha. 1986). Selective weed control practices are often needed Treatments were applied in separate experiments on to enhance and hasten shrub establishment and return April27, 1987, September 15, 1987, and May 13, 1988. the investment in seed, seedbed preparation, fencing, Other treatments included hand-weeding and untreated and deferment. Various weed control strategies have checks. Herbicides were applied in water at a total vol­ increased the survival and growth of tree plantings in ume of 1.9 Uplot using hand-held sprayers. Trifluralin semiarid regions (Felker and others 1986). The objective was incorporated 3 to 5 em deep with garden rakes imme­ diately after application, just prior to planting fourwing saltbush seed. All other herbicides were applied immedi­ ately after seeding, without incorporation. The experi­ Paper presented at the Symposium on Cheatgrass Invasion, Shrub Die­ Off, and Other Aspects of Shrub Biology and Management, Las Vegas, NV, ments were arranged as randomized complete blocks with April 5-7, 1989. four replications. Soil water contents were maintained Joseph L. Petersen and Darrell N. Ueckert are Research Associate and Range Ecologist, respectively, Texas Agricultural Experiment Station, at field capacity by frequent irrigation with garden sprin­ 7887 N. Hwy. 87, San Angelo, TX 76901. Matthew W. Wagner is Biologist klers to assure seed germination, emergence, and estab­ II, Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, lishment offourwing saltbush. The study sites were TX 78744. fenced to eliminate rodents, lagomorphs, and livestock. 305 This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain. Phytotoxicity of the herbicides to fourwing saltbush was Phytotoxicity of the herbicides to fourwing saltbush quantified by counting the live seedlings 15 and 90 days plants was estimated 15 and 90 DAT by visually ranking after treatment (DAT) and by measuring seedling heights percent necrosis in each plot (0 percent = no visible injury, 90 DAT. Canopy cover (percent) of grasses and broad­ 100 percent = no live tissue visible). Efficacy of the treat­ leafedweeds was visually estimated in five 0.1-m2 ran­ ments for weed control was estimated 90 DAT by visually domly located quadrats in each plot 90 DAT. Grasses estimating weed canopy cover from five 0.1-m2 randomly and broadleafed weeds were then harvested at ground located quadrats in each plot. Grasses and broadleafed level and dried to a constant weight at 50 °C for estimates weeds in the quadrats were then harvested at ground of standing crop. level and dried to a constant weight at 50 oc for estimates of standing crop. The data were subjected to analyses of variance. Trans­ Postemergence Herbicide formations of percentage data did not affect data interpre­ Experiments tation, so actual values are presented. Results from the Field experiments were established to evaluate the April 1987 and May 1988 experiments with preemergence effects of selected postemergence herbicides on fourwing herbicides were similar, thus the data were pooled. Means were separated by Duncan's multiple range test (P 0.05) saltbush seedlings. Plots were 3 by 3m and separated = where appropriate. by 1.2-m borders. Plots were rototilled and packed just prior to planting seed and transplanting seedlings. Four age classes offourwing saltbush plants occurred in each RESUL~PREEMERGENCE plot when treatments were applied. These included: HERBICIDES (1) 1-month-old seedlings, hand planted at 8 g/2.4-m row, 1.3 em deep, about 6 weeks prior to treatment. The Preemergence applications of metolachlor and alachlor number of seedlings present at time of treatment ranged had little effect on emergence or growth of fourwing from 12 to 80/plot; (2) 4-month-old seedlings (seven/plot), saltbush seedlings. Shrub seedling densities in plots transplanted on 38-cm centers 1 month prior to treat­ treated with metolachlor or alachlor were similar to ment; (3) 9-month-old seedlings (seven/plot), transplanted those in hand-weeded plots after 90 days (table 1). on 38-cm centers 1 month prior to treatment; and ( 4) 2- However, shrub seedling densities were significantly year-old, stem-cut seedlings (five/plot), transplanted on lower (P = 0.05) in plots treated with trifluralin, oryzalin, 61-cm centers 6 months before treatment. One row of and ethalfluralin than in hand-weeded plots after 90 each plant age class was included in each plot. days. Seedling emergence and establishment were much Seeds used for the first three age classes were pur­ lower following autumn seeding compared to spring seed­ chased from a commercial source harvested in western ing, but the responses to autumn herbicide applications Texas. The stem-cut seedlings were from mature plants were generally similar to those observed for spring of an accession from Texon, TX, growing in a nursery at treatments. the Research Center. The plots were frequently irrigated The preemergence herbicides did not affect saltbush as discussed earlier. seedling heights compared to heights of seedlings in hand­ Herbicide treatments applied postemergence to the weeded plots (table 1). The high mortality of saltbush weeds June 16, 1988 included acifluorfen {5-[2-chloro-4- seedlings during the first 3 months after planting in well­ (trifluoromethyl)phenoxy]-2-nitrobenzoic acid} at 0.56 kg prepared seedbeds with hand weeding and frequent irri­ a.i .lha, metsulfuron {2-[[[[( 4-methoxy-6-methyl-1,3,5- gation indicated that poor stand establishment in these triazin-2yl)amino]carbonyl]amino]sulfonyl]benzoic experiments was partly related to poor seed quality, low acid} at 0.04 kg/ha, sulfometuron {2-[[[[(4,6-dimethyl-2- inherent vigor of seedlings, or both. pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid} at 0.05 kglha, fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2- pyridinyl]oxy]phenoxy]propanoic acid} at 0.21 kg/ha, and Table 1-Fourwing saltbush seedling densities (No./2.4-m row) 30 clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) at 0.28 and 90 days (d) and heights (mm) 90 days after spring or kg/ha. Herbicide treatments applied on October 4, 1988 autumn applications of selected preemergence herbicides were the same as above except that metsulfuron and sul­ near San Angelo, TX 1 fometuron were applied' at 0.02 kg/ha based on results Average seedling from the first experiment. Broadleafed and grass weeds densities Average seedling were actively growing and varied phenologically from the 2 Treatment S~ring Autumn height at 90 d two-leaf stage to flowering at time of herbicide application Herbicide Rate 30d 90d 30d 90d S~ring Autumn in both experiments.