Developing a flowering threshold with corn earworm in soybeans

Helicoverpa zea (Boddie), corn earworm, can be a damaging insect pest of many crops in the southern U.S., including soybeans. In North Carolina, a reproductive threshold includes soybeans in their flowering and pod filling stages. Flower feeding may directly impact soybean yields by reducing the number of potential pods, but this relationship is poorly understood.  This research is designed to illuminate the interactions of soybean and corn earworm by determining the yield impact of corn earworm feeding during the flowering stages of soybeans.  A split-plot design experiment was set up during the summers of 2011 and 2012 in eastern North Carolina and the flowering stages of soybeans were studied in relationship to pesticide manipulated insect pressure. An insect pressure two times the normal reproductive threshold during 2011 and 2012 field seasons did not significantly affect yield. This suggests that the reproductive threshold may be too conservative when soybeans are in their flowering stages because they have the ability to compensate for loss during pod and seed filling stages. Also, during the summer of 2012, there was a correlation between corn earworm pressure and the number of injured flowers further suggesting that flower feeding did not significantly affect soybean yield.