Evaluation of Organic Pest Management Treatments for Bean Leaf Beetle and Soybean Aphid⎯Neely-Kinyon Trial, 2006

The soybean aphid (Aphis glycines Matsumura) is native to China and Japan, and was a new pest in Iowa in 2000. Aphid numbers were high in the 2001, but in 2002 and 2003, aphids appeared to be less of a problem. This small, yellow aphid has distinct black cornicles (“tailpipes”) on the tip of the abdomen and develops colonies on soybean plants as winged and wingless forms. Aphids feed through piercing-sucking mouthparts. The winged form has a shiny black head and thorax with a dark green abdomen and black cornicles. The soybean aphid is the only aphid in North America that will reproduce on soybeans. Therefore, any small colony of aphids found on soybeans must be soybean aphids. The aphid may have up to 18 generations per year, beginning with overwintering eggs on the alternate host of buckthorn trees. These eggs hatch into nymphs and two generations of wingless females develop on buckthorn, before the winged generation flies to soybean fields in the spring. Winged generations appear on soybean plants in the case of crowding from wingless colonies, and in the fall, a winged generation migrates back to buckthorn. These females produce a wingless generation that mates with winged males and lay eggs on the buckthorn trees. Soybean aphid populations build and peak during the period between late seedling stage to blooming stage. Usually in late July, the aphids move from the terminal area of the plant to the undersides, making control more difficult. Honeydew and sooty mold (the excrement of the aphid and the resulting black fungus that grows on it) are apparent in August and September. Stunted plants, reduced pods and seeds may result from aphid feeding. Also, soybean aphids can transmit viruses that cause mottling and distortion of the leaves and a reduced seed set. Discolored seeds may also result from this infection.