Soybeans can tolerate a fair amount of foliage feeding before bloom, or about 30 percent defoliation. During and after bloom that tolerance drops considerably to about 15 percent defoliation. Regular scouting should be going on now to monitor defoliation.
Soybeans have been blooming in a large number of South Carolina fields in the Pee Dee region. Foliage feeding caterpillars can be found pretty easily now when scouting.
Be sure to check at least two separate areas of the field and sample each area twice. If you cannot make a clear decision whether or not to make a treatment after that, check an additional area or two.
If fields are found to be over threshold, labeled insecticides and there rates can be found in the Soybean Insect Control section of the SC Pest Management Handbook, along with additional scouting information and thresholds.
Here are a few different caterpillars active now in soybean fields: