As glyphosate-resistant weeds continue to proliferate across the Mid-South, many producers have taken a renewed interest in residual herbicides for the control of problem weeds such as Italian ryegrass and Palmer amaranth.
For a number of years, one of the mainstay residual herbicides in soybean weed control systems was metribuzin (Sencor/Lexone). Metribuzin provides residual control of a number broadleaf species and is also an effective tool in burndown combinations with paraquat and glufosinate. It is especially effective as a soil-applied residual when combined with other herbicide modes-of-action (MOA) such as in the products Boundary, Authority MTX, Canopy, Matador and others.
Metribuzin is a PSII inhibitor (Group 5) which offers a unique MOA in soybean and one that may help reduce the potential evolution of herbicide resistance to the more commonly used PPO-inhibiting herbicides (Group 14) such as Flexstar and Valor.
One of the drawbacks to metribuzin use is the sensitivity of some soybean varieties to this herbicide. Soil types, organic matter, rainfall, product use rate, among others can all play a role in soybean sensitivity to metribuzin.
Previous research at Mississippi State University has shown that metribuzin sensitivity of soybean can be quantified through greenhouse screenings but this research has not been conducted in the last several years.
Due to the need of alternative herbicide options, a research project conducted by Mississippi State University and the University of Arkansas screened some of the modern germplasms available to producers for metribuzin tolerance. The link below will take you to the results of this study.
Soybean tolerance to metribuzin is broken down into slight (1-3), moderate (4-6), severe (7-9) and death (10). It should be noted that the majority of varieties exhibited acceptable tolerance to metribuzin (slight-moderate), but there were a few varieties that were very sensitive to metribuzin and extreme caution or alternative weed control options should be explored with these varieties. While this list is not exhaustive, it will help give an idea of the sensitivity of some modern day cultivars.
Whether or not the soybean variety you intend to plant is listed, prudence and following label recommendations should still be used with any herbicide.