Abstract
A field experiment was conducted in 2017 and 2018 to evaluate the sensitivity and recovery of grain sorghum to the simulated drift of glufosinate, glyphosate, and paraquat at two application timings (V6 and flag leaf growth stage). Paraquat drift caused maximum injury to sorghum plants in both years, whereas the lowest injury was caused by glyphosate in 2017. Averaged over all herbicide treatments, injury to grain sorghum from the simulated herbicide drift was 5% greater when herbicides were applied at flag leaf stage, as compared to herbicide applications at the six-leaf stage in 2017. In 2018, injury from glyphosate drift was higher when applied at the six-leaf stage than at the flag leaf stage. Paraquat and glufosinate drift caused more injury when applied at flag leaf stage than at six-leaf stage at 14 days after application in 2018. About 21% to 29% of injury from the simulated drift of paraquat led to a 31% reduction in grain sorghum yield, as compared to a nontreated check in 2017. The simulated drift of glyphosate and glufosinate did not result in any significant yield reduction compared to the nontreated check in 2017, possibly due to the recovery of sorghum plants after herbicides’ drift application.
Highlights
Weed control in grain sorghum (Sorghum bicolor (L.) Moench) is mostly achieved through spraying herbicides such as atrazine, S-metolachlor, dimethenamid-P, and alachlor for preemergence weed control and 2,4-D, dicamba, prosulfuron, and bromoxynil for postemergence weed control [1] grain sorghum is sensitive to many herbicides, including glyphosate, glufosinate, and imazethapyr [2].In the southern United States, including Mississippi, grain sorghum is commonly grown adjacent to corn (Zea mays L.), cotton (Gossypium hirsutum L.), or soybean (Glycine max (L.) Merr.) [2] and it becomes subjected to herbicide drift from these adjacent fields
At 14 days after application (DAA), grain sorghum injury was highest from the simulated drift of paraquat (29%) and lowest from glyphosate (3%) drift in 2017, when data was averaged over application timings (Figure 1)
Similar to 14 DAA, the injury to grain sorghum from herbicide drift at 28 DAA was greater with paraquat (21%) than glufosinate (7%) and glyphosate (4%) by 14 and 17%, respectively (Figure 2)
Summary
In the southern United States, including Mississippi, grain sorghum is commonly grown adjacent to corn (Zea mays L.), cotton (Gossypium hirsutum L.), or soybean (Glycine max (L.) Merr.) [2] and it becomes subjected to herbicide drift from these adjacent fields. Off-target movement of herbicides applied in corn, cotton, or soybean, is common when environmental conditions favor volatilization and/or physical drift [2]. Factors influencing the severity of the herbicide drift may include a sensitive crop, crop growth stage, environmental conditions, herbicide and formulation, droplet size, spray additive(s) and pressure, and the height of the boom [2]. Aside from harvest aids, glyphosate and glufosinate are applied for postemergence (POST) weed control in the Roundup Ready®
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