Submitted to: Journal of Crop Improvement
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2011
Publication Date: 4/22/2011
Citation: Ding, W., Reddy, K.N., Krutz, L.J., Thomson, S.J., Huang, Y., Zablotowicz, R.M. 2011. Biological response of soybean and cotton to aerial glyphosate drift. Journal of Crop Improvement. 25:291-302. Interpretive Summary: Glyphosate usage and application frequency within a year have increased with the adoption of Roundup Ready (RR) cropping systems. This trend has created an environment conducive to glyphosate drift problems. Glyphosate drift complaints from ground or aerial applications are common in the Mississippi Delta. Scientists at Crop Production Systems Research Unit, Stoneville, Mississippi have conducted a drift study to determine the effects of glyphosate drift from aerial application on plant injury, chlorophyll, shikimate accumulation, plant height, and shoot dry weight in non-RR cotton and non-RR soybean. The biological response of soybean and cotton to glyphosate drift decreased with increased distance from the edge of spray swath. The glyphosate drift effect was highest at the edge of the spray swath and lowest at 35.4 m downwind distance. At 35.4 m downwind, shoot dry weight (5-13%) and plant height (6-8%) were reduced in both crops at 3 WAA. These biological data suggest that both crops are sensitive to glyphosate but soybean is more sensitive to glyphosate drift than cotton.
Technical Abstract: An aerial application drift study was conducted in 2009 to determine biological effects of glyphosate on cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.]. Glyphosate at 866 g ae/ha was applied using an Air Tractor 402B agricultural aircraft in an 18.3 m spray swath to crops at the two- to three-leaf stage. Visual plant injury, chlorophyll, shikimate, plant height, and shoot dry weight were determined at 1, 2, and 3 weeks after application (WAA) of glyphosate. Biological responses differed between crops as a function of downwind drift distance. For example, at 3 WAA soybean was dead 6 m downwind from the spray swath, while cotton sustained 85% visual injury. Plant injury was not observed beyond 25.6 m downwind in soybean and 35.4 m downwind in cotton at 3 WAA. Chlorophyll reduction was higher (80%) in soybean compared to cotton (43%) at 0 m from the edge of the spray at 1 WAA. Shikimate levels 1 WAA decreased from 1518% at 0 m to 209% at 35.4 m downwind in soybean; at the same sampling time shikimate levels in cotton decreased from 464% at 0 m to 0% at 35.4 m. At 35.4 m downwind, shoot dry weight (5-13%) and plant height (6-8%) were reduced in both crops at 3 WAA. The biological response of soybean and cotton to glyphosate drift decreased with increased distance from the edge of spray swath. These biological data suggest that soybean is more susceptible to glyphosate drift than cotton and elevated shikimate level could be used as a sensitive indicator to confirm plant exposure to glyphosate drift.