WEED BIOLOGY AND ECOLOGY, AND DEVELOPMENT OF SUSTAINABLE INTEGRATED WEED MANAGEMENT SYSTEMS FOR COTTON, SOYBEAN, CORN
Location: Crop Production Systems Research Unit
Title: Biological responses to glyphosate drift from aerial application in non-glyphosate-resistant corn
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 21, 2010
Publication Date: July 7, 2010
Citation: Reddy, K.N., Ding, W., Zablotowicz, R.M., Thomson, S.J., Huang, Y., Krutz, L.J. 2010. Biological responses to glyphosate drift from aerial application in non-glyphosate-resistant corn. Pest Management Science. 66:1148-1154.
Interpretive Summary: The widespread adoption of Roundup Ready (RR) crops in the United States has led to an unprecedented increase in glyphosate usage in recent years. 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 visual injury, chlorophyll, shikimate accumulation, plant height, and shoot dry weight in non-RR corn. Visual injury and other biological responses point to same conclusion, that is, injury from glyphosate aerial drift was highest at edge of the spray swath and decreases gradually with increased distance. The glyphosate drift effect was lowest (0 to 18% visual injury, 2 to 10% dry weight reduction) at 35.4 m downwind distance. The LD50 distance, the distance that glyphosate drift must travel to cause 50% reduction in biological responses ranged from 12 to 26 m. The visual injury estimation was rapid and non-destructive and as reliable as chlorophyll, shikimate, plant height, and plant dry weight determination method.
Glyphosate drift from aerial application onto susceptible crops is inevitable, yet the biological responses to glyphosate drift in crops are not well characterized. The objectives of this research were to determine the effects of glyphosate drift from a single aerial application (18.3 m swath, 866 g ae/ha) on visual injury, chlorophyll content, shikimate level, plant height and shoot dry weight in non-glyphosate resistant (GR) corn. One week after application (WAA), corn was killed at 3 m from edge of the spray swath with injury decreasing to 18% at 35.4 m downwind. Chlorophyll content decreased from 78% at 6 m to 22% at 15.8 m and chlorophyll content was unaffected beyond 25.6 m at 1 WAA. Shikimate level in corn was 349% higher at 0 m compared to shikimate level in corn at 35.4 m upwind. Shikimate level decreased from 333% at 3 m to 93% at 15.8 m and shikimate levels were unaffected beyond 25.6 m downwind. Plant height and shoot dry weight decreased gradually with increased distance. At a distance of 35.4 m, corn height was reduced by 14% and shoot dry weight by 10% at 3 WAA. Visual injury and other biological (chlorophyll, shikimate, and plant height and shoot dry weight) responses point to same conclusion, that is, injury from glyphosate aerial drift is highest at edge of the spray swath and decreases gradually with distance. The LD50 (the lethal distance that drift must travel to cause a 50% reduction in biological response) ranged from 12 to 26 m among the biological parameters when wind speed (stable in direction) was 11.2 km/h and using a complement of CP-09 spray nozzles on Air Tractor 402B agricultural aircraft.