Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
Continue to watch for defoliators as well as spider mites in both full season and double crop soybean fields. In full season soybeans in the pod fill stage, the defoliation threshold drops to 10-15% defoliation. Remember, double crop soybeans cannot tolerate as much defoliation since they often do not reach the leaf area index needed for maximum yields.
You should also scout for stinkbugs and pods worms as we enter the pod set and pod fill stages. Open canopy blooming soybeans will be attractive to egg laying corn earworm moths, especially in drought stressed areas where corn will dry down early. Corn earworm trap catches have started to increase and we are starting to hear about fields to the south with economic levels of corn earworm. However, only time will tell if this will translate into a major podworm outbreak in soybeans in our area. Although we are finding a few corn earworms in full season soybeans, this is not unusual for this time of year and only scouting on a routine basis will tell you if you have an economic problem. In the past, we have used the treatment threshold of 3 corn earworms per 25 sweeps in narrow fields and 5 corn earworms per 25 sweeps in wide row fields (20 inches or greater). These are static thresholds that were calculated for a 10-year average soybean bushel value of $6.28. A better approach to determining a threshold is to access the Corn Earworm Calculator (http://www.ipm.vt.edu/cew/) which estimates a threshold based on the actual treatment cost and bushel value you enter.
For more information on what is happening in soybeans in Virginia – please refer to their Virginia Ag Pest Advisory (http://www.sripmc.org/Virginia/).