Herbicide-resistant kochia and waterhemp continue to spread and are problematic for many North Dakota soybean farmers. Effective postemergence herbicide options are becoming more limited as resistance to glyphosate and dicamba is becoming more frequent in these weeds. Soil residual herbicides are an important component to management of weed populations with resistance to multiple herbicide sites of action. Metribuzin and sulfentrazone are two older soil residual herbicides that can be effective against most problematic broadleaf weeds. Application rates of metribuzin and sulfentrazone are often lower than maximum labeled rates due to concerns of crop injury to soybean. Recent research conducted in Fargo concludes that higher rates of metribuzin (up to 12 oz ai/A; 16 oz/A of a dry 75% formulation) and sulfentrazone (up to 6 oz ai/A; 12 fl oz/A of a 4 lb formulation) provide greater than 90% control of waterhemp for up to 6 weeks after planting. Furthermore, no soybean injury was noted across multiple trial years. The rates used in that research are often 3-4X higher than standard application rates across the state. That research was conducted on a clay loam with a single soybean cultivar, so the goal of this research is to evaluate higher rates of these products on different soil types and weed species across the state for weed control and crop injury.

-Determine risk of crop injury from metribuzin and sulfentrazone on different soil types across the NDSU Research Extension Centers
-Determine weed control from multiple rates of metribuzin and sulfentrazone at these same locations

-Trials will be on display at Weed Science and REC Field Days that are open to the public
-Results will be shared at Extension and Scientific meetings

The project will evaluate crop safety and herbicide efficacy on waterhemp and kochia at 5 different sites across North Dakota. Crop safety information will be region-specific on typical soil types near each trial location, which will help generate confidence to use these products at higher rates. The weed control information with show the benefit of each active ingredient at 2 rates, and a mixture of both active ingredients to emphasize their role in season-long control of kochia and waterhemp.