Residual Herbicides for Soybean

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

It is important to include effective broad spectrum residual herbicides at the time of burndown application or at plant (for conventional tillage soybeans). Including a residual herbicide is the first step, using the correct herbicide is the next decision, and the most difficult is the correct rate. The following link includes a table of some of the better soil applied herbicides and the corresponding rates. For no-till soybeans, I prefer to use a pre-package mixture that contains both an ALS-inhibiting herbicide (Group 2) and a PPO-inhibiting herbicide (Group 14). The ALS product will help with burndown control and provides more consistent control in trashy fields. The PPO also may help with burndown, but generally provides a broader spectrum of control than ALS herbicides alone. The two most common Group 2 herbicides for soybeans are chlorimuron (Classic, Canopy, Envive, and others) and cloransulam (FirstRate, Sonic, Authority First, Gangster, and others). In order for the ALS inhibiting herbicide to provide more consistent burndown control and provide adequate length of residual control the chlorimuron and cloransulam rates should be 0.02 to 0.027 lbs active ingredient per acre; which translates to 1.25 to 1.7 oz of Classic or 0.4 to 0.5 oz of FirstRate. A lot of the literature from the companies does not recommend these rates because they are not considering applications at least 14 days prior to planting, or they are not accounting for the residual herbicide to help with burndown. A table to compare various pre-packaged mixtures and comparable rates of chlorimuron and cloransulam can be found at http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2011/04/Soybean-Residual-Comparisons_11.pdf.

 

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