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Crop Biotech Update

Comparative Losses of Glyphosate and Residual Herbicides in Conservation-tilled Watersheds

June 17, 2011

Residual herbicides from conservation tillage in corn and soybean production are usually detected in surface water at concentrations that exceed the U.S. maximum contaminant levels (MCL) and ecological standards. Thus, it has been recommended to use glyphosate tolerant crop varieties and replace other residual herbicides (alachlor, atrazine, linuron, and metribuzin) with glyphosate which has a shorter half-life and strongly sorbed in soil. To compare the losses of herbicides in watersheds, USDA scientists Martin Shipitalo and Lloyd Owens applied glyphosate and selected residual herbicides in two plowed and two no-till watersheds in a two-year corn and soybean rotation and monitored herbicide losses for three years.

Results showed that the average dissolved glyphosate loss is less than the losses of atrazine, alachlor, and linuron, regardless of tillage practice. Glyphosate concentration exceeded the MCL only once during the time of the study. Therefore, use of glyphosate with glyphosate-tolerant crops in replacement of residual herbicides is expected to reduce effects of crop production in the surface water quality.

Read the research article at