These small (1/4 inch) yellowish-buff to reddish beetles usually sport four distinct black spots on their back. A small proportion of the beetles lack spots, but all color forms have a black triangle at the base of the wing covers. The bean leaf beetle attacks soybeans throughout the growing season. Overwintering adults colonize early-emerging soybean fields, but beetle feeding on cotyledons and unifoliolate leaves does not reach economic threshold. There is one generation in the north and two in the south of Minnesota per year. Larvae feed underground on soybean roots and nodules, but this feeding does not appear to affect yield. Emerging adults from the first generation feed on soybean leaves in July and should be treated if defoliation exceeds 35% and beetles are still feeding. Adults from the second generation should be treated in late August if defoliation exceeds 25% during pod-set and pod-fill. These adults also feed on pods, which affects seed development and allows disease entry. Consequently, these beetles should be treated if damaged pods exceed 10%, or if adults exceed 0.5 per plant, during pod-fill. Heavy populations should be watched closely and treated aggressively if pod clipping is noted.
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URL: http://www.soybeans.umn.edu/crop/insects/leaf_beetle.htm
Last Modified
3/25/11 2:16 PM
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