By Justin McMechan.
A significant number of soybean gall midge adults (Figure 1) were collected from this year’s soybean fields in east-central and northeast Nebraska. In east-central, adult numbers ranged from 2 to 38 adults per location on July 16. In the northeast, a total of 22 adults from this year’s soybean were collected for the first time on July 15 from near Pilger. No adults have been collected from this year’s soybean at the Randolph or Belden sites. Dead and dying plants have been observed near infested sites in both northeast and east central Nebraska. Orange and white larvae are still being observed on infested plants in these same fields. If you have gall midge in your county and its not documented, contact any of the authors of this article.
Figure 1. Adult soybean gall midge collected from a single cage south of Ceresco, Nebraska.
Three additional counties were identified as infested with soybean gall midge in 2019 (Figure 2). Many of you may be concerned about the number of adults we collected from these fields. It’s important to note that the placement of cages was based on infested plants increasing the likelihood for capturing adults whereas cages used to collect adults from the overwintering generation were placed in areas where gall midge larvae were expected but not known to be present in large numbers.
Figure 2. Counties documented as infested in 2018 (red) and 2019 (orange).
Management
The emergence period of soybean gall midge adults from this year’s soybean field (1st generation) is likely to be as long as what was observed for the overwintering population (last year’s soybean fields). Extended emergence will greatly reduce the likelihood that insecticide will have enough residual activity to control this population. Growers with soybean fields planted in early- to mid-May in high pressure areas have likely already observed infestations in their fields and it would be difficult to gain any control with another application. However, growers who planted around June 1 may have missed the overwintering generation and it might be practical to take action on those fields. This information is based on a planting date study at the Eastern Nebraska Research and Extension Center nead Mead that found infestations around 45-47% for plantings on May 1 and May 15 but only at 3% for June 1 plantings. Fields late-planted on June 15 and July 1 had no signs of infestation.