Crop & Pest Report
Bean Leaf Beetle in Soybeans (8/11/11)
Economic numbers of bean leaf beetles have been reported near the Woodworth area in Stutsman County. With more soybean acreage in North Dakota, bean leaf beetle populations have been slowly increasing over the past years.
Adult bean leaf
beetles emerge from overwintering sites and move into soybean or dry bean
fields during the seedling stage. Adults are yellow to reddish-brown and have three
to four black spots with a black border on wing covers. The white larvae
develop in the soil, feeding on the roots and nodules. New adults emerge in August
and feed on foliage and pods. Feeding injury to leaves appears as small round
holes between the leaf veins. Injury to pods appears as lesions similar in size
and shape to leaf-feeding holes. The injury to pods results in secondary
infections by fungi and bacteria, causing rotting and discoloration.
Treatment thresholds from other regions are 3 to 7 beetles per sweep or based on defoliation - 50% defoliation during early vegetative, 40% defoliation during pre-bloom, 35% defoliation during bloom and 20-25% defoliation or 10% pod feeding (or the presence of clipped pods). Late season feeding on the foliage and pods by the new adults that emerge in August appears to be more important than early season feeding. This may increase the risk of virus transmission and cause secondary infections (rotting and discoloration) from fungi and bacteria.
Janet J. Knodel, Extension Entomologist
NDSU Crop & Pest Report - May 24, 2012
