Project Details:

Aphids and midges - something old and something new in Iowa Soybean

Parent Project: This is the first year of this project.
Checkoff Organization:Iowa Soybean Association
Categories:Insects and pests
Organization Project Code:023065
Project Year:2021
Lead Principal Investigator:Erin Hodgson (Iowa State University)
Co-Principal Investigators:

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

My research lab has the nation’s largest soybean aphid efficacy evaluation program, and has mainly focused on foliar insecticide performance. I have access to new products or improved formulations before they are commercially available, and farmers can see performance data of new products compared to standard insecticides. I want to grow my program beyond foliar insecticides with additional management tools like host plant resistance. My research is novel in that I 1) use replicated plots to compare seed- and foliar-applied insecticides, 2) collect intense data on soybean aphid seasonal exposure, and 3) present unbiased data from multiple industry companies.

Project Objectives

During the summers of 2021-2023, experimental plots will be used to evaluate insect management tactics, like seed treatments and foliar insecticides (see previous reports here: These tactics will be evaluated alone and in combination to determine optimum yield protection. Plots will be established at high-risk locations in Iowa each summer.

1) Soybean aphid. At one location, 20-30 treatments will be replicated four times in a randomized complete block design using a 30" row spacing. Treatments will include a range of insecticidal groups and application sites. Aphid population dynamics will be monitored weekly in addition to secondary pest activity (e.g., beetles, mites, stink bugs, caterpillars, etc.). Foliar applications will be based on our established treatment threshold for soybean aphid. At the end of each season, yield will be collected and compared to cumulative aphid days for each treatment.

2) Soybean gall midge. At two locations, 20-30 treatments will be replicated four times in a randomized complete block design using a 30" row spacing. Midge larval will be monitored weekly in addition to secondary pest activity (e.g., soybean aphid, beetles, mites, stink bugs, etc.). A combination of seed-applied and foliar treatments will be evaluated. Foliar applications will be based on our observation of overwintering adult emergence (See 2a). At this point, that is our “best guess” for targeting adult movement into soybean. At the end of each season, yield will be collected and compared to insect activity for each treatment.

Project Deliverables

Expected Outputs: Data collected every summer will become publically available:
• Yellow Book for Soybean Insects is free and available electronically at my lab website.
• Arthropod Management Tests publication will be generated annually. These publications are nationally recognized for insecticide efficacy evaluations and available to Entomological Society of America members.
• Regular updates about soybean aphid, soybean gall midge, and other pests are available throughout the year through ICM News and ICM Blog.

Progress of Work

Updated April 1, 2021:
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 5-year average. Soybean acres were up 200,000 compared to 2019 (9.4 million acres planted). In August, a derecho moved through central Iowa and impacted ~6 million acres of field crops. Drought was prevalent in western Iowa and reached “Extreme Drought” or D3 status in northwestern Iowa.

Soybean pests were highly variable throughout the state. Many caterpillars and beetles 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. We treated plots when aphids reached the economic threshold on 10 August. Most of the cumulative aphid day (CAD) pressure was evident in August, but there were significant differences in yield responses. Warrior II CS had the most CAD and had significantly more aphids than most other treatments. Cruiser 5FS, an insecticidal seed treatment, had the second highest CAD. Transform WG and Endigo ZCX had generally more CAD than other foliar insecticidal treatments. With the help of ISU graduate student Ivair Valmorbida, we were able to confirm this population of aphids 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 31 counties. 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. Growth stage V2 foliar sprays were made on 9 June 2020 at the ISU Northwest Research Farm and 4 June 2020 at the Griswold Farm. Foliar sprays were made 10 days after adult emergence on 25 June 2020 at the ISU Northwest Research Farm and 22 June 2020 at the Griswold Farm. Injury was light at both locations and yield did not appear to be significantly impacted by soybean gall midge at either location.

View uploaded report PDF file

Updated October 25, 2021:

Final Project Results

Updated October 25, 2021:
Spring planting conditions throughout Iowa were excellent and ahead of historical planting records. In general, drought conditions were evident and field in western Iowa, in particular, were stressed. Abnormally dry or moderate drought conditions persisted throughout the entire growing season.
Population fluctuations between locations and years is typical soybean aphid dynamics for Iowa. Soybean aphids arrived on soybean in July, which is average for Iowa. Soybean aphid colonization was initially patchy and continued to grow at a slow pace.
I was able to complete proposed work, including research and extension related to soybean aphid management. I established a foliar insecticide efficacy evaluation at one location in 2021 (ISU Northwest Research Farm). I had 25+ treatments at this location; however, aphids did not approach the economic threshold.
Soybean gall midge continues to emerge as an economic pest in Iowa. Three new counties were confirmed with infestations (total of 31 counties), and expanded to over 120 total counties in five states (IA, MN, MO, NE, SD). I dedicated many extension programs to soybean gall midge and spoke about the limited information on biology, life cycle and management. Overall, severity of commercial fields was less than in 2019 and infestations tended to be more scattered within fields. I established efficacy evaluations at two locations in 2021. Multiple chemistries and sites of application were used, but emphasis was placed on suppressing overwintering adult establishment. Our 25+ treatments did not appear to delay or effectively suppress larval feeding.

View uploaded report Word file

What does it mean for farmers: Effective management tactics are still limited for soybean gall midge, 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.
• Additional insecticides may be required to suppress additional emergence.

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.

Benefit to Soybean Farmers

• increase our understanding of soybean gall midge biology, life cycle and population dynamics [long term knowledge];
• recognize soybean aphid, soybean gall midge, and other soybean pests [short term skill];
• improve general pest management approaches, including the effect of multiple pests and the potential for cumulative injury [short term skill];

Performance Metrics

• implement scouting and adopt economic thresholds for soybean pests [long term skill];
• understand the implications for soybean aphid genetic resistance to insecticides [long term knowledge];
• reduce insecticide use, including seed and foliar treatments [long term skill]; and
• improve profit margins by reducing input costs [long term knowledge].

Project Years