Pyrithiobac sodium controls nightshade without long-term effect on cotton

Nightshades are some of the most difficult weeds to control in Upland Acala varieties of cotton. A herbicide in the newest class of acetolactase synthase inhibitors has been developed for use as a selective over-the-top broadleaf herbicide in cotton. Studies were conducted in Upland Acala cotton varieties in 1991, 1992 and 1993 to evaluate the efficacy of Staple (pyrithiobac sodium) in controlling nightshade. The herbicide was applied as early postemergence, mid-postemergence and sequential applications at rates of 0.25, 0.50, 0.75, 1.0, 2.0 and 3.0 oz of active ingredient per acre (ai/acre). Acceptable nightshade control was achieved at all rates, when applied as a single application or as sequential applications, except for the 0.25 and 0.50 oz ai/acre applications. The best control was achieved when the herbicide was applied at rates of 1.0 to 3.0 oz ai/acre over the top of cotton in the cotyledon to eight true-leaf stage, with nightshade in the cotyledon to six-leaf stage. Cotton injury symptoms were evident with all treatments at 7 days after application but were nonexistent by 90 days after application. There was no evidence to indicate that pyrithiobac sodium has any long-term effect on cotton growth and development or on cotton lint yield.