Issue No. 17, Article 6/July 21, 2006
Numbers of Soybean Aphids Still Small, But Keep Watching
Our weekly surveys of soybean fields in Woodford County (10 fields) and Stephenson County (10 fields) and six fields in between those two counties continue to reveal small numbers of soybean aphids. However, in Stephenson County in particular, the numbers have increased weekly since early July. As of July 18, all 10 fields surveyed were infested with soybean aphids, with the average density ranging from 0.55 to 5.85 aphids per plant. All six of the "transect fields" (one field each in Marshall, Putnam, Bureau, Lee, Whiteside, and Ogle counties) also were infested, with the average density ranging from 1.45 to 22.75 (Lee County) aphids per plant. As many as 115 soybean aphids were found on one of the 20 plants sampled in the field in Lee County. Seven of the 10 fields surveyed in Woodford County were infested with soybean aphids, with the average density ranging from 0.05 to 2.35 aphids per plant in the infested fields.
These numbers of soybean aphids are way, way below the threshold of 250 aphids per plant, but the increasing numbers bear watching. Once again, I remind you that development of soybean aphid populations slows down or declines when temperatures exceed 90°F, but a return to gentler temperatures will benefit population buildup.--Kevin Steffey