Last week's edition of the Bulletin described which soil-residual corn herbicides can be applied after corn emergence. This week brings an analogous discussion of soil-residual soybean herbicides. Soybean planting has recently proceeded at a rapid pace, and it's altogether likely that fields were planted before soil-residual herbicides were applied. If a certain number of days have elapsed since planting or if soybean plants have begun to emerge, proceeding with the planned application depends on the herbicide.
Only a few herbicides that are most frequently applied before soybean planting or emergence can be applied after soybean plants have begun to emerge. Several soybean herbicide active ingredients can cause severe injury if applied directly to the soybean plant or close to emergence. Labels often restrict application timing relative to soybean planting (for example, within 3 days of planting) and/or to visible signs of soybean emergence. Keep in mind that, in general, the potential for soybean injury increases as the interval between application and planting decreases. Crop genetics and environmental factors, such as timing of precipitation in relation to herbicide application and soybean planting or emergence, also influence the potential for soybean injury.
Not all soil-residual soybean herbicides that can be applied after soybean emergence will control emerged weeds, so additional management procedures (such as adding a herbicide with postemergence activity) may be needed if weeds also have emerged. Table 1 summarizes information about postemergence applications of the more traditional soil-applied soybean herbicides. Please consult product labels for additional information, such as the need for tank-mix partners or spray additives to improve control of existing weeds.