Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Soybeans
As the potential for late season insect control increases, be sure to check all labels for the days from last application to harvest, as well as other restrictions. You will also need to scout carefully for earworms during the next week. Today’s blacklight trap catch is showing a dramatic increase in moth catches throughout Kent and Sussex counties, and we can readily find moths laying eggs in fields – especially double-crop fields.
As of today we continue to find sporadic numbers of corn earworms in soybean fields; however, this can quickly change so be sure to scout all fields. Information from VA and areas to the south indicates that they are starting to spray fields; however, populations vary in the south based on the degree of drought stress in corn, as well as differences in corn maturity. As we know, when corn dries down, the moths emerging from larvae found in corn fields will lay eggs in soybeans. The only way to know if you have an economic level will be to scout. In the past, we have used the treatment threshold of 3 corn earworms per 25 sweeps in narrow-row fields and 5 corn earworms per 25 sweeps in wide-row fields (20 inches or greater). However, these are static thresholds that were calculated for a 10-year average soybean bushel value of $6.28. With higher soybean prices, the best 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.