By Robert Wright
High numbers of woolly bear caterpillars are reported in some soybean fields in south central Nebraska. Pay particular attention to late maturing soybean fields. These act as a magnet for woolly bear caterpillars and many other insects; especially those that can fly, such as grasshoppers, bean leaf beetles, and southern corn rootworm beetles.
Large caterpillars and adult grasshoppers are more difficult to kill with insecticides. There are several soybean insecticides labelled for control of caterpillars, including woolly bear caterpillars. Many of these products contain a pyrethroid insecticide either by itself or mixed with other active ingredients.
One thing to watch for is that many of these pyrethroid containing insecticides have a 21-30 day preharvest interval. Products containing permethrin (e.g. Ambush 2EC, Arctic 3.2EC) have a 60 day preharvest interval (PHI). Products containing gamma-cyhalothrin (e.g. Proaxis, Declare) have a 45 day PHI. Some products prohibit or limit grazing or harvesting soybean hay for feed. Be sure to read the label before applying an insecticide.
Source : unl.edu