No. 22 Article 3/September 1, 2006

Soybean Aphids Still Present in Soybean Fields, But the Threat Has Dissipated

Our weekly survey of soybean aphids in 26 fields continues, but soybean development is past the stage when economic damage would occur. Although densities of soybean aphids approached the economic threshold of 250 aphids per plant in one field in Stephenson County on August 11 (Stephenson 7, Table 1), the density in that same field on August 21 had declined to 156.1 aphids per plant. None of the densities of soybean aphids in the 26 fields surveyed from August 10 through August 22 (Table 1) reached the economic threshold. Densities in some fields continued to increase from August 10 to August 22, whereas densities in other fields either reached a plateau or declined during the same time period.

As soybeans mature and leaves begin to drop from the plants, soybean aphid colonies will produce winged aphids, which will begin leaving soybean fields in search of their overwintering host, buckthorn. Some of these flying aphids will be captured in suction traps scattered around the Midwest, and the numbers captured this fall might give us some insight into the potential population of soybean aphids in 2007. With the relative absence of multicolored Asian lady beetles in most areas and most soybean fields having low to moderate numbers of soybean aphids, the present outlook for soybean aphids in 2007 is good (bad for us). However, this outlook could change between now and next spring, and summer temperatures in 2007 also will have an effect. We'll simply have to wait and see.--Kevin Steffey

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