Yield losses associated with Dectes stem borers in soybean, and efficacy of fipronil seed treatment, Garden City, and Scandia, KS, 2008

Fipronil soybean seed treatments were evaluated in large plots at three locations in southwest Kansas. Thrips populations were high on the soybean seedlings at Garden City (GC) locations, and we found that the fipronil seed treatment was effective in suppressing thrips populations (60%) at both locations near GC. Dectes populations were low at GC south (23% of plants infested). At GC north and Scandia, however, there were substantial Dectes populations (84, and 75% plants infested, respectively). The fipronil seed treatment was extremely effective in reducing the Dectes stem borers, giving 96 to 100% control. The fipronil seed treatment did not affect grain yield at GC south, where Dectes infestations were low. However, at GC north, the fipronil seed treatment increased grain yield 6.5 bu/a at normal harvest and 9.7 bu/a at late harvest. This increase was 5.6 and 7.6 bu/a at Scandia, respectively. These results reveal a significant physiological yield loss of 10.2 and 8.2%, and a plant lodging loss of 5.0 and 2.9% at GC north and Scandia, respectively, associated with Dectes stem borer infestations.