Field Evaluation of Auxin Herbicide Volatility Using Cotton and Tomato as Bioassay Crops

Abstract

Research was conducted to compare cotton and tomato response to volatility of 2,4-D, dicamba, and triclopyr formulations. Herbicide treatments were applied to tilled soil during August and September, and potted plants were placed in the center of treated strips. To quantify injury, leaf cupping/crinkling/drooping; leaf rolling/strapping; stem epinasty; and stem swelling/cracking were each visually rated on an injury scale of 0 to 5 (0 = none, 1 = slight, 2 = slight to moderate, 3 = moderate, 4 = moderate to severe, and 5 = severe). Leaf cupping/crinkling/drooping injury averaged across herbicide treatments at 1× rates was 1.0 for cotton and 2.0 for tomato 14 d after treatment (DAT). Averaged across crops, leaf cupping/crinkling/drooping injury for the 1× rates 14 DAT was equivalent for the 2,4-D dimethylamine (DMA) salt, 2,4-D acid, dicamba DMA salt, dicamba diglycolamine (DGA) salt, dicamba acid, and triclopyr acid formulations and ranged from 1.1 to 1.8. For tomato, the only herbicide treatments with injury 14 DAT no greater than for the nontreated were 1× rates of 2,4-D DMA and 2,4-D acid for leaf rolling/strapping (1.0); 2,4-D acid, dicamba DMA, dicamba acid, and triclopyr acid for stem epinasty (0.3 to 0.7); and 2,4-D DMA, 2,4-D acid, dicamba DMA, dicamba DGA, dicamba acid, and triclopyr acid for stem swelling/cracking (0.1 to 0.2). A weighted factor assigned to each injury criterion provided an overall total injury estimate of 0 to 100%. When applied at 1× rates, total injury for 2,4-D isooctyl ester was 10% for cotton and 36% for tomato and for triclopyr butoxyethyl ester was 11% for cotton and 50% for tomato. For the 2,4-D DMA, 2,4-D acid, dicamba DMA, dicamba DGA, dicamba acid, and triclopyr acid formulations, total injury was 4 to 8% for cotton and 20 to 24% for tomato, and for both crops, injury was no greater than for the nontreated.