Evaluation of management strategies for bean leaf beetles (Coleoptera: Chrysomelidae) and Bean pod mottle virus (Comoviridae) in soybean.

Cerotoma trifurcata Förster (Coleoptera: Chrysomelidae) and Bean pod mottle virus (Comoviridae) (BPMV) both can reduce yield and seed quality of soybean, Glycine max (L.) Merr. Field experiments were conducted to evaluate the effects of systemic, seed-applied, and foliar-applied insecticides for the management of this pest complex at three locations in central, northeastern, and northwestern Iowa during 2002-2004. Seed-applied insecticide was evaluated according to a currently recommended management program for Iowa (i.e., insecticide applications that target emerging overwintered beetles, F0, and the first seasonal generation, F1 ). The experimental treatments included seed-applied (thiamethoxam, 0.3-0.5 g [AI] kg(-1)] or clothianidin, 47.32 ml [AI] kg(-1)) and foliar-applied (A-cyhalothrin, 16.83-28.05 g [AI] ha(-1)) or esfenvalerate (43.74-54.69 g [AI] ha(-1)) insecticides. Applications of the foliar insecticides were timed to target F0, F1 or both F0 and F1 populations of C. trifurcata. Our results confirm that insecticides timed at F0 and F1 populations of C. trifurcata can reduce vector populations throughout the growing season, provide limited reduction in virus incidence, and improve both yield and seed coat color. Furthermore, seed-applied insecticides may be the more reliable option for an F0-targeted insecticide if used within this management strategy. An F0-targeted insecticide by itself only gave a yield improvement in one out of eight location-years. However, by adding an F1-targeted insecticide, there was a yield gain of 1.42-1.67 quintal ha(-1), based on contrast comparisons at three location-years.