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Bean Leaf Beetle Adults Can Be Found in Early-Planted Soybeans

May 18, 2001
In last week's Bulletin (issue no. 7, May 11), we presented some life cycle information and management tips for bean leaf beetles. During the past week, we've received a few calls from producers concerning soybean seedling injury caused by bean leaf beetle feeding. However, densities of bean leaf beetles should be much lower than last year. Entomologists at Iowa State University have developed a predictive model to estimate the overwintering success of bean leaf beetle adults. In the May 7, 2001 issue of the Integrated Crop Management Newsletter, they predicted a 95% mortality level for bean leaf beetle adults in northern and central Iowa. For southern Iowa counties, the predicted mortality level is 84%. These predictions are in stark contrast to the low mortality (statewide average = 41% mortality) of bean leaf beetle adults during the winter of 1999 to 2000 in Iowa. Despite the fact that mortality was very severe during the most recent winter, entomologists at Iowa State University still predict moderate infestations of bean leaf beetles this summer. This prediction is based on the abundant snow cover and the large population of bean leaf beetle adults that represented the overwintering population. The past several warm winters have allowed bean leaf beetle densities to build to very impressive levels. Based on the predictions offered by our colleagues at Iowa State University, we anticipate low overwintering survival of bean leaf beetle adults in the northern one-third of Illinois. Larger densities of bean leaf beetle adults are expected for central and southern Illinois counties.

Many, many bean leaf beetle adults are required to deliver an economic punch (16 per foot of row in the early seedling stage, 39 per foot of row at stage V2+). Rescue treatments for the great majority of soybean fields are never required. Research conducted by Larry P. Pedigo, an entomologist with Iowa State University, allows producers to effectively evaluate the wisdom of applying a rescue treatment based on bean leaf beetle adult densities, projected market value of soybeans, and the cost of a rescue treatment (Table 2). Before any treatment decision is made for bean leaf beetles, please consult Table 2.--Mike Gray

Author: Mike Gray

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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