Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu
Field Corn
You may have seen a recent article in the Delmarva Farmer regarding a detection of a new pest of field corn in Pennsylvania, the Western Bean Cutworm. In the article, the field crop entomologist from Penn State talked about this insect and how the first moths were found this year in northern PA. However, as far as I know, they have not found any fields with larval damage. This pest has been increasing in importance in the Corn Belt. We did set out two trapping sites in 2008 and no moths were detected all season. There is a good article, as well as video, in this week’s C.O.R.N. Newsletter from Ohio State (http://corn.osu.edu/#C) about this pest. Although we do not anticipate finding this pest in Delaware for a few years, please let us know if you suspect an infestation.
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. Be sure to scout carefully for earworms during the next few weeks. Local trap catches, as well as traps to our south, are showing an increase in moth activity.
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. 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.
Green cloverworm are still of concern in double crop soybeans with defoliation exceeding 20% in a number of fields throughout the state. We still have not seen enough diseased larvae to indicate that the population is crashing. Continue to scout for soybeans aphids as well, especially in later planted fields. Remember the threshold is 250 aphids per plant with the populations rising up until the R-5 and in some cases R-6 stage of plant development. You should also watch for beneficial insect activity that can help control populations.