As glyphosate-resistant weeds continue to be a major concern for soybean producers in Arkansas, many producers are relying on residual herbicides for control of problem weeds like Palmer amaranth. Metribuzin (Sencor/Lexone) is a PSII inhibitor (Group 5) herbicide that provides residual control of a number of annual grasses and broadleaf species. Metribuzin is especially effective as a soil-applied residual when in combination with other herbicide modes-of-action (MOA) such as the products Authority MTZ, Boundary, and Canopy to name a few.
One weakness to metribuzin use is the sensitivity of some soybean varieties to this herbicide. Other environmental factors including: soil texture, organic matter content, rainfall, and product use rate, may also play a role in this sensitivity. In 2012, the University of Arkansas Division of Agriculture screened all soybean varieties entered into the 2012 Arkansas Soybean Performance Tests. Varieties were screened in a greenhouse, and an application rate equivalent to 0.5 lb ai/ac metribuzin was applied pre-emerge. Seedlings were rated after emergence. The link below will take you to the results of this study. The varieties were rated according to the following scale: tolerant (<1), slight (1-3), moderate (4-6), severe (7-9) and death (10).
Many combination products (Authority MTZ, Boundary, etc.) have use rates that contain lower amounts of metribuzin than what was used for this study. With these reduced rates, soybean varieties may display a lesser amount of damage than what is reported here. Therefore, extreme caution or alternative weed control options should be explored for varieties rating moderate and above.