Update:
The 2020-2021 winter was relatively warm compared to previous years in Iowa (mean temperature of 27.85 degrees in December). April had cooler than average temperatures but planting conditions were favorable throughout much of the state. Planting progress was about two weeks ahead of the average. Soybean acres were up 500,000 compared to 2019 (9.9 million acres planted). Drought was prevalent in western Iowa and reached “Extreme Drought” or D3-4 status in some Iowa counties in August.

Soybean pests continue to be highly variable throughout Iowa. Several caterpillar and beetle species were present, but generally at non-economic levels. Soybean aphids arrived to Iowa soybean in July. Aphid populations were initially patchy and slowly spread within and between fields. In August, some populations grew quickly and exceeded the economic threshold. Sometimes, populations peaked in late August or early September. Although soybean aphids did not reach the economic threshold in our research plots, we noted plots sprayed with pyrethroids did not yield as well as other treatments. With the help of ISU graduate student, Ivair Valmorbida, we were able to confirm this aphid population to be pyrethroid-resistant.

In addition to soybean aphid, soybean gall midge was prevalent in some Iowa soybean fields. This soybean pest is particularly devastating and can cause plant death. Affected plants were restricted to field edges and economic loss could be 100%. I continue to address questions and concerns about soybean gall midge. This new pest was confirmed along western Iowa in 35 counties (4 new county detections in 2021). I had several field experiments in western Iowa in 2021. I dedicated many extension programs to soybean gall midge and spoke about the limited information on biology, life cycle and management. Adult soybean gall midge emergence began mid-June and midge-infested plants were found shortly after. Adult emergence was almost completely continuous throughout the summer, with three generations of adults being observed.

What does it mean for farmers: Effective management tactics for soybean gall midge are still limited for this pest, but our recommendations for best efforts to reduce the severity of plant injury are to:
• Plant soybeans last in areas (e.g., late May or early June) where heavy soybean gall midge pressure has been observed in previous years.
• Scout field edges first for initial detection of infested plants.
• Apply foliar insecticides at the time of adult emergence, typically around V3-V5 growth stages. Perimeter treatments may be a more cost-effective strategy at early vegetative growth.

What does it mean for farmers: Population fluctuations between locations and years is typical soybean aphid dynamics for Iowa. Our recommendation for soybean aphid management in Iowa is to:
• Strongly consider using host plant resistance if soybean aphid populations are persistent and the seed agronomic traits are appropriate for the area. The use of a pyramided gene will result in lower seasonal accumulation and reduce the need for foliar insecticides.
• Plant early if the field is in an area with persistent soybean aphid populations.
• Scout for soybean aphid, especially during R1–R5, and use a foliar insecticide if aphids exceed the economic threshold of 250 per plant.
• Use a product labeled for soybean aphid; most well-timed applications of foliar insecticides will provide yield protection if applied at the economic threshold and coverage is sufficient.
• Evaluate foliar insecticide efficacy three days after application to ensure soybean aphid populations were sufficiently reduced.
• Understand that late-season accumulation of aphids (i.e., after R5) may not impact yield like it does in early reproductive growth; a foliar insecticide applied after seed set may not be an economically profitable choice.