Monday, August 20, 2012

Updated bean leaf beetle thresholds

Summer is winding down fast, but some areas in Iowa still have respectable numbers of bean leaf beetle. The second generation is coming out and could cause direct injury to soybean pods. If your beans are still developing, it might be a good time to go out and take some sweeps.

 Bean leaf beetles can be confused with southern corn rootworm and other beetles. Look for four dark spots on the forewings, and a dark triangle behind the "neck." Photo by Marlin E. Rice. 

Overwintering and first generation bean leaf beetles rarely cause direct economic damage to soybean in Iowa; plants compensate for defoliation in many ways. But they can transmit bean pod mottle virus that can impact the market value of food grade soybean. Bean leaf beetle can cause direct injury to pods during the seed fill stage depending on when the second generation emerges. 

Bean leaf beetles can eat about 0.2 pods per day. Note they don't eat all the way through the pod, like grasshoppers can. Photo by Mark Licht, ISU Extension. 

Last year I had several questions about treatment thresholds for bean leaf beetle given our higher market values. With the help of ISU entomology grad student, Mike McCarville, we created a dynamic threshold calculator. It's a downloadable Excel file where you plug in your market value and control costs. Visit this ICM News article and scroll to the bottom for the link the calculator. To learn more about bean leaf beetle biology and management, click here.

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