Metribuzin Tolerance Screening for KY Soybeans

Due to multiple-herbicide resistance, pigweeds such as palmer amaranth and waterhemp are becoming increasingly difficult to manage in Kentucky. Fortunately, some older herbicide chemistries such as metribuzin and paraquat are still effective for managing pigweeds in soybeans, even when multiple herbicide resistance is present in the pigweed populations (Norsworthy 2024). Unfortunately, metribuzin is not used as much as it should be in Kentucky soybeans. Furthermore, early planting of soybeans is leaving metribuzin in the soil for longer periods of time before the pigweeds germinate in the late spring and early summer thus reducing the efficacy of metribuzin in early-planted soybeans. Metribuzin use in Kentucky soybeans could be improved in a couple of ways; firstly, the doses of metribuzin applied as a pre-emergent herbicide could be increased in Kentucky soybean production. Secondly, a second dose of metribuzin could be sprayed on top of early planted soybeans before the pigweeds germinate thus replacing the metribuzin in soil which has been broken down by microbes. However, soybean producers would rightfully be hesitant to use these methods because of the danger of crop injury from the metribuzin.