Control of Glyphosate and Acetolactate Synthase Resistant Common Ragweed (Ambrosia artemisiifolia L.) in Soybean (Glycine max L.) with Preplant Herbicides

Abstract

A population of common ragweed in Ontario was confirmed to be resistant to glyphosate in 2011. Group 2 [acetolactate synthase (ALS) inhibitors] resistant common ragweed was first confirmed in Ontario in 2000. Previously, glyphosate provided excellent control of common ragweed in glyphosate resistant soybean but with the confirmation of glyphosate resistant (GR) common ragweed, alternative herbicides need to be evaluated. Eight field trials with preplant herbicides were completed over two years (2013 and 2014) in fields with confirmed GR common ragweed. Tank-mixes of glyphosate and linuron or metribuzin provided 88% - 99% and 86% - 98% control 4 weeks after application (WAA) and 80% - 92% and 80% - 95% control 8 WAA, respectively. However, these herbicides also had among the highest environmental impact of the herbicides tested. Based on the results of these studies, GR common ragweed can be controlled with residual herbicides when applied preemergence in soybean. Currently, there are no post emergence herbicides that provide adequate control of GR common ragweed, therefore, preemergence herbicides with residual are essential for full season control.