By Jeremy Ross, Extension soybean agronomist
Every year, varieties entered into the University of Arkansas System Division of Agriculture’s Soybean Performance Trials are screened for tolerance to metribuzin. Metribuzin (Sencor, Canopy, etc.) is a PSII inhibitor (Group 5) herbicide that provides residual control of an assortment of annual grasses and broadleaf weeds in soybean, including Palmer amaranth. With the extensive use of PPO (Group 14) and chloracetamide (Group 15) herbicides in soybean and rotational crops such as corn and cotton, use of an additional mode of action (MOA) is a sound strategy to reduce the risk of resistance to these other herbicide MOA’s.
The handicap to metribuzin use is the sensitivity of soybean varieties to this herbicide. Other environmental factors, including: soil texture, organic matter, rainfall, soil pH, and product use rate, may also play a part in sensitivity. The University of Arkansas System Division of Agriculture conducted a greenhouse screening of soybean varieties, testing their tolerance to metribuzin at a rate of 0.5 lb ai/A or 10.67 oz/A of a 75DF metribuzin product. Soybean varieties are given a rating of either Slight Injury, Moderate Injury, or Severe Injury based on results from the greenhouse screening. Results are available here and under the publications tab on the AR Row Crops blog webpage as well as the Soybean page at uaex.edu.