Soybean Tolerance to Sulfentrazone and Metribuzin.

With glyphosate resistant weeds becoming more prevalent, the demand for soil residual herbicides applied preemergence (PRE) in soybean is increasing. Sulfentrazone and metribuzin are two commonly used soil applied herbicides that may be used to manage glyphosate-resistant waterhemp and Palmer amaranth. However, soybean varieties have displayed differential tolerance to these herbicides. The objective of this experiment is to evaluate methodology to determine the sensitivity of soybean varieties to metribuzin and sulfentrazone. Two different methods were evaluated across several trials. With the first method, soybean were planted into a blend of field soil, sand, and potting mix and herbicides were applied to the soil surface prior to soybean emergence. Evaluations of visual soybean injury and plant height were made every seven days until 21 days after emergence. Plants were harvested at 21 days after emergence and dry weight determined. For the second methods experiment, soybean seeds and seedlings were soaked in four different concentrations of sulfentrazone and metribuzin for 24 hours. Seeds or seedlings were then planted in potting mix and evaluated for emergence rate, height, and visual injury every seven days for 14 days. The soil applied herbicide method allowed differentiation between susceptible and tolerant varieties when sulfentrazone was applied at 0.14 kg ai/ha. However, further research is needed to identify optimal soil applied metribuzin rates and methods to determine soybean tolerance. Results for imbibition experiment with sulfentrazone were inconsistent while no injury was observed from imbibing seeds with any concentration of metribuzin.