Influence of Planting Date and Insecticide on the Bean Leaf Beetle (Coleoptera: Chrysomelidae) Abundance and Damage in Nebraska Soybean

Abstract

A field study was conducted in Dodge County, Nebraska to determine the effect of planting date and the use of a soil insecticide at planting on the abundance and damage by the bean leaf beetle, Cerotoma trifurcata (Forster), on soybean Glycine max (L.) Merrill. There were 2 generations per year, and overwintered beetles were highly attracted to the earliest planted soybean fields. Few overwintered beetles were observed in late planted soybean. A planting time in-furrow application of carbofuran 15 G at 1.12 kg(AI)/ha significantly reduced the number of colonizing beetles and subsequent defoliation, but there were no significant differences in seed yield. Pod feeding by 2nd-generation beetles began in August and continued until late September. Accumulated percentage of pod damage was significantly less in plots treated at planting compared with untreated plots in both 1989 plantings, and only in the late 1990 planting. However, seed quality and seed yields were not significantly different. Except during rare outbreak years, bean leaf beetles on soybean in Nebraska can likely be successfully managed without the use of insecticides.