Tank-mix adjuvants to reduce the adverse effect of muddy rain on the activity of paraquat against winter wild oat

This study was designed to determine the adverse effect of soil settling on a weed through a simulated muddy rain on the activity of a bipyridylium herbicide and to compare the efficacy of three adjuvants to decrease this adverse effect. In a greenhouse experiment, a 0.04-mm muddy rain containing 0, 1, 2, 4 and 8 kg soil ha(-1) was rained on winter wild oat before the doses of 0, 75, 150, 300, 600, and 1200 g paraquat ha(-1) were sprayed on. In a companion experiment, a 0.04-mm muddy rain containing 0 and 8 kg soil ha(-1) were rained on winter wild oat before the aforementioned doses of paraquat were sprayed with or without acriflavine chloride, chlormequat chloride, and mepiquat chloride at 0.2% (w/v). Based on the dose giving 90% dehydration of the plant, the muddy rain containing 1, 2, 4, and 8 kg soil ha(-1) decreased the activity of paraquat against winter wild oat in run 1 by 1.2-, 1.6-, 2.5-, and 7.0-fold and in run 2 by 1.4-, 3.0-, and 6.4-fold in comparison with control, respectively. All adjuvants were effective in significantly decreasing the adverse effect of muddy rain on the activity of paraquat against winter wild oat. In this regard, chlormequat chloride was the most effective, following by acriflavine chloride and mepiquat chloride.