Spring Wheat Response to Simulated Glyphosate Drift

Abstract

Core Ideas Drift prior to stem elongation may go unnoticed, yet producers can expect yield reductions up to 15% Drift encountered during stem elongation and the appearance of the flag leaf will result in yield losses that can exceed 85%. Symptomology of drift that occurs during heading is very innocuous, as no stunting will be observed and yellowing of leaf tissue can easily be mistaken for symptoms of Septoria leaf blotch. Glyphosate is one of the most widely used nonselective herbicides. The nearly ubiquitous use of glyphosate‐resistant soybean [Glycine max (L.) Merr.], corn (Zea mays L.), sugar beet (Beta vulgaris L.), and/or canola (Brassica napus L.) cultivars in the Northern Great Plains can, unfortunately, result in off‐target movement to sensitive crops. Off‐target movement generally exposes a sensitive crop like spring wheat (Triticum aestivum L.) to rates ranging from 1 to 10% of the applied rate. The objective of this study was to measure the effect of simulated glyphosate drift at a concentration of 0.07 lb acid equivalent/acre on spring wheat crop injury, crop residue, and yield. At 28 d after treatment (DAT), crop injury varied from none to 67.5%. Across years, the application at Zadoks GS17 resulted in the most crop injury, with symptoms typical of glyphosate injury as the crop was severely stunted and yellow at 28 DAT, resulting in yield losses between 82 and 96% of the untreated control. Glyphosate residue could be detected at 7 DAT for all treatments, but the number of false negatives increased to over half at 21 DAT. No clear quantitative relationship could be discerned from the amount of glyphosate residue detected and the application timing.