Pre-emergence Herbicides for Weed Management in Soybean

Liz Bosak, Outreach Specialist, Department of Agronomy, University of Wisconsin-Madison

Pre-emergence herbicides can lower the risk of developing herbicide resistance and add flexibility to the post-emergence application timing. For an excellent discussion of how a two-pass herbicide program can reduce resistance risk, please read Boerboom et al.’s “An Equation for Trouble? Glyphosate x Weeds = Resistance” article, . To see the utility of a residual herbicide applied at planting in less than 90 seconds, watch Purdue University’s time lapse video of Palmer amaranth growth in two plots, with and without a pre-emergence herbicide application, . When choosing a pre-emergence herbicide, there are a few factors to consider in the decision making process:

1. Select a PRE herbicide with a different site-of-action than the POST herbicide that you will be using. Download the TakeAction Herbicide Classification chart, , or use their lookup tool on your android phone, iphone, or ipad . For instructions, see this webpage .

2. Match the PRE herbicide effectiveness with the weed species on your farm. Efficacy information is available in summary tables located in A3646 Pest Management in Wisconsin Field Crops, (scroll down to download the pdf, soybean pp. 143-144, corn pp. 23-37 ) or in yearly research reports published online, .

Remember to apply the full labeled rate at the appropriate time. Once the application has been made, scout the field after crop emergence to determine the effectiveness of the pre-emergence application and to plan for the post-emergence application. For more information on herbicide resistance management, please consult the following fact sheet .