Evaluation of herbicide treatments for the control of creosotebush (<i>Larrea tridentata</i>)

TitleEvaluation of herbicide treatments for the control of creosotebush (Larrea tridentata)
Publication TypeReport
Year of Publication1969
AuthorsGould W.L., Herbel C.H.
Series TitleResearch Progress Report, Western Society of Weed Science
Date Published1969
InstitutionResearch Progress Report, Western Society of Weed Science
Keywordscresotebush, desert rangeland, herbicide treatments, invasion, Larrea tridentata
AbstractCreosote bush is an evergreen xerophyte which has invaded extensive areas of desert rangeland in the Southwestern United States. Much of the infested area at one time was productive grassland, but drought and grazing by livestock has shifted the balance in favor of the brush so many areas are heavily infested with creosote bush and nearly devoid of grass. Control of the creosotebush is necessaryto effect revegetation. Creosote bush sprouts profusely from the crown when the topgrowth is removed mechanically. Satisfactory seeding methods have not been developed for the arid Southwest, so chemical treatments must be used which will selectively remove the brush and leave the grass. Treatments were applied on the Jornada Experimental Range near Las Cruces, New Mexico, from 1961 through 1965 to determine the most effective herbicides and the optimum date of application for the control of creosote bush. Simulated aerial application was made on 1/100 acre plots at 2-week intervals from July through October or November. In one year (1963), treatments were initiated in April. Treatments in 1961 included 2,4-D, 2,4,5-T, 2,4-DP, silvex, 2,3,6-trichlorobenzoic acid and amitrole-T. In 1962, dicamba wasadded to the list of herbicides and in 1963 picloram was added. The herbicide rate at each application date was 1/2 lb/A in 1961 and 1962, 1 lb/A in 1963 and 1 1/2 lb/A in 1964 and 1965, except that picloram was applied at 3/8 lb/A in 1963. On one spray date in 1962, 1963 and 1964, herbicides were applied at three rates to help elucidate the optimum herbicide rate. The dates of maximum toxicity, as determined by evaluating the degree of defoliation 2 years after herbicide application, varied yearly from late July to early November, but generally in a given year all the herbicides caused maximum defoliation on a common date of application. Treatments during September caused the highest degree of defoliation in 3 of the 5 years. Highest levels of defoliation occurred from treatments with dicamba, picloram and 2,3,6-TBA on 3 different dates in 2 of the years. Very little defoliation was obatined from treatments applied before July. This would indicate that creosotebush is most susceptible to herbicides when treated after the summer rainy season has started.