Soybean aphids are insects native to Asia that have the potential to seriously reduce soybean yields. They are a small insect (typically less than 1/8 of an inch), green to yellow in color, with twin black “tailpipes” on their abdomen. Soybean aphids generally begin colonizing soybeans in early June in Minnesota and other northern states. In August, these aphids begin migrating south, usually reaching this area of Missouri by late August or early September. Populations of soybean aphids increase rapidly, doubling about every 2-3 days.
Soybean aphids damage plants in one of three ways: removal of sap, reduction in photosynthesis, or transmission of viral diseases. During the vegetative stage of soybean, heavy infestations of these aphids result in stunted plants and poor canopy development. During the reproductive stages, aphid feeding results in poor pod and seed set. Usually, soybean aphid damage is not of major concern in Henry County. However, with many late-planted fields this year, soybean aphids have the potential to affect yields.
Soybean aphid infestations range from just a few insects per plant up to several thousand insects per plant. The economic threshold for soybean aphid in Missouri is 250 insects per plant. Levels beyond this economic threshold have already been reached north of I-70. Although it is still unlikely that soybean aphid populations will have a major impact on yields in this area, it is still a good idea to scout for these pest over the next couple of weeks, especially if you have beans that were planted in mid to late July. There are a number of recommended insecticides for control of soybean aphids. For more information, contact Travis Harper at the Henry County Extension Center by phone (660)885-5556 or email harpertw@missouri.edu.