Master of Science (MS)
Plant, Enviromental and Soil Sciences
Availability of dicamba- and 2,4-D-resistant crops will provide alternative weed management options, but the risk of off-target movement of herbicides to sensitive crops is of concern. Soybean [Glycine max (L.) Merr.] treated with diglycolamine (DGA) salt of dicamba at 4.4 g ae/ha (1/128 of the recommended use rate of 560 g/ha) at V3/V4 (two to three trifoliate) was injured 39% 14 days after treatment (DAT) and injury was 97% with 280 g/ha (1/2 of use rate). For application at R1 (first flower), injury 14 DAT was 23% at 1.1 g/ha (1/512 of use rate) and was 68% at 70 g/ha (1/8 of use rate). Soybean yield for dicamba at 4.4 g/ha was reduced 4% when applied at V3/V4 and 10% at R1; for 17.5 g/ha (1/32 of use rate), yield was reduced 16% at V3/V4 and 36% at R1. Research was also conducted to evaluate volatility of various formulations of 2,4-D applied at 1,120 and 2,240 g ae/ha; dicamba applied at 560 and 1,120 g/ha; and triclopyr applied at 1,680 and 3,360 g ae/ha. Herbicides were applied to tilled soil and potted cotton (Gossypium hirsutum L.) and tomato (Solanum lycopersicum L.) plants were placed in treated strips. Injury was visually rated using four criteria (leaf cupping/crinkling/ drooping; leaf rolling/strapping; stem epinasty; and stem swelling/cracking) and a severity scale of 0 to 5 (0= no injury and 5= severe). A weighted factor assigned to each injury criterion provided an estimate of total injury on a 0 to 100% scale. Only leaf cupping/crinkling/drooping injury was observed for cotton and total injury 14 DAT was no more than 11% for the 1x rates of the herbicides and formulations. Total injury for tomato for the 1x rates of 2,4-D isooctyl ester was 36% 14 DAT and injury was attributed primarily to stem epinasty and stem swelling/cracking. For the 2,4-D dimethylamine (DMA) and acid formulations and for the dicamba DMA, DGA, and acid formulations, total injury for tomato was equivalent and was as high as 24% for the 1x rates. Injury to tomato with triclopyr butoxyethyl ester was 2.1 times that of triclopyr acid.
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Bauerle, Matthew John, "Evaluation of Volatility and Physical Drift of 2,4-D, Dicamba, and Triclopyr Formulations" (2014). LSU Master's Theses. 39.