Management of Amaranthus rudis S. in glyphosate-resistant corn (Zea mays L.) and soybean (Glycine max L. Merr.)

Field studies were established at two locations in Missouri to determine Amaranthus rudius (common waterhemp) control by single or multiple pre-emergence and/or postemergence herbicide strategies in glyphosate-resistant corn and soybean. The corn study assessed five herbicide strategies: pre-emergence alone; mid-postemergence alone; early postemergence followed by mid-postemergence; pre-emergence followed by mid-postemergence without glyphosate; and pre-emergence followed by glyphosate mid-postemergence. The soybean study assessed four herbicide strategies: mid-postemergence alone; early postemergence followed by mid-postemergence; pre-emergence followed by glyphosate mid-postemergence; and pre-emergence followed by mid-postemergence without glyphosate. In corn, pre-emergence herbicides suppressed A. rudius growth and development 7–34 days longer, compared to the untreated control. The strategies with single herbicide applications provided 21–99% control of A. rudius, while the multiple application strategies provided 84–100% control of A. rudius. In soybean, the presence of pre-emergence herbicides suppressed A. rudius emergence and growth for 7–31 days, compared to treatments with no herbicide application. A single herbicide application provided 69–100% control of A. rudius, and the multiple application strategies were more consistent with 77–100% control. Effective season-long management of A. rudius in glyphosate-resistant corn and soybean should include sequential herbicide applications.