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.
Highlights
IntroductionMerr.) is an important crop in Ontario with approximately 800,000 hectares grown annually [1]
Eight field experiments were conducted over a two-year period (2013 and 2014) in fields with confirmed multiple resistant (Group 2 and 9) common ragweed to determine the efficacy of preplant (PP) herbicides in glyphosate resistant (GR) soybean
The addition of flumioxazin to glyphosate plus chlorimuron resulted in slightly higher control from 27% to 72%. These results are in contrast to the results reported by Pollard [6] where greater than 80% control was achieved with a tankmix of glyphosate and chlorimuron
Summary
Merr.) is an important crop in Ontario with approximately 800,000 hectares grown annually [1]. Soybean is used for livestock feed and human consumption in the form of oil and specialty food [1]. Soybean is seeded from late April until early June. This timing coincides with the emergence of many summer annual weeds, including common ragweed. These weeds can be controlled with a preplant or post emergence herbicide application, with glyphosate being the most widely used
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