Characterizing and Utilizing Metribuzin Tolerance in Soybeans to Improve Weed Management Strategies in Early Planted Soybeans

Metribuzin is becoming an increasingly popular herbicide in soybean production systems due to the emerging resistance of weeds to glyphosate, glufosinate, synthetic-auxins and PPO- inhibitors. However, many producers are limited in their ability to apply metribuzin because it can only be applied as a pre-emergent herbicide in soybeans and some soybean varieties are sensitive to metribuzin, causing heavy injury to susceptible varieties if metribuzin is applied. With this project we hope to expand the use of metribuzin in soybeans by identifying more natural variants leading to metribuzin tolerance in soybeans and beginning to work those variants into soybean germplasm adapted to the southern United States. Additionally, this work will allow more weed management options for early planted soybeans by allowing a second application of metribuzin over top the soybeans extending the time metribuzin can act a pre- emergence herbicide in soybean systems. Currently, pre-emergent metribuzin applications will not last long enough in early soybean systems to control palmer amaranth and waterhemp which germinate in late May or early June. Although, we have already identified a major QTL for metribuzin tolerance in maturity group 4, 5, and 6 soybeans, identifying lines/QTL in late maturity group 3 and early maturity group 4 would allow for post-emergence metribuzin. For this project we will identify QTL(s) that confer metribuzin resistance in late maturity group 3 and early maturity group 4, screen advanced breeding lines for the QTL identified and make crosses to accumulate desirable combinations of metribuzin tolerance loci in soybeans bred for early planted soybean.