Metribuzin is an important herbicide for controlling numerous weed species in wheat. It is primary a soil-residual herbicide which can be applied in the fall after the wheat emerges and roots become well established. It is particularly effective on annual bluegrass (Poa annua) and has good activity on several annual broadleaf weed species, such as chickweed (Stellaria media) and corn buttercup (Ranunculus arvensis). Metribuzin is also a critical herbicide in the management of Italian ryegrass (Lolium perenne ssp. Multiflorum). Weed competition during the fall and winter can reduce plant health, development of wheat tillers and grain yield potential.
However, wheat varieties differ in tolerance to metribuzin and many currently available varieties have not been screened for metribuzin tolerance, particularly in the soft red winter wheat production area of the Mid-South. Mississippi State University evaluated wheat varieties included in the 2013 MSU Wheat Variety Trials for tolerance to metribuzin. Wheat varieties were assessed in a field research study at the R.R. Foil Plant Science Research Center at Mississippi State University (Starkville, MS). The soil classification at this study location is a Stough fine sandy loam with a CEC of 6.6, soil pH of 6.0 and organic matter content of 0.72%. Metribuzin (Sencor 75DF) was applied at a rate of 12 oz/acre which corresponds to 0.56 lbs ai/acre. The metribuzin rate utilized for this study represented a much higher use rate than normal, and was intended strictly for evaluation of herbicide tolerance. At the time of metribuzin application, wheat had 4 or more leaves, but had not substantially initiated tillering (late Feekes growth stage 1). Visual ratings of herbicide injury were taken 11, 28 and 59 days after herbicide application. Grain yield of metribuzin-treated and untreated plots of each wheat variety were also collected and used to assess tolerance. Wheat variety sensitivity to metribuzin data are summarized according to classifications ranging from tolerant to susceptible (T=Tolerant; MT=Moderately Tolerant; MS=Moderately Susceptible; S=Susceptible). Variety sensitivity was based upon visual discoloration of foliage, vegetative stunting, stand reduction, and yield loss.
These results should help you better assess potential for crop injury when using the herbicide metribuzin. This data was derived from one study and additional trials will be conducted to strengthen these evaluations of variety tolerance. Always follow herbicide label instructions and use caution when using this or any herbicide.