Management of Insecticide-resistant Soybean Aphids

Soybean aphids, Aphis glycines, (Figure 1) are the most significant insect pest of soybean in Minnesota, Iowa, North Dakota and South Dakota. Development of insecticide resistance in this pest creates new challenges for effective soybean pest management and profitable soybean production.

Photo Credit:

Photo courtesy of R. Koch, University of Minnesota

Figure 1. Soybean aphids infesting a soybean leaf

Resistance is defined as a decrease in susceptibility of a pest population to an insecticide that may result in failures when the product is used according to label recommendations for that pest.

Failures of certain pyrethroid insecticides for management of some soybean aphid populations have been observed in commercial fields (Figure 2), and resistance to bifenthrin and lambda-cyhalothrin has been documented through small-plot research, laboratory bioassays and molecular research. Because of the mobility of winged soybean aphids, the challenges posed by insecticide-resistant populations of the pest could spread to soybean fields in other parts of the region.

Photo Credit:

Maps courtesy of B. Potter, University of Minnesota

Figure 2. Counties with reported failures of pyrethroids for control of soybean aphid. Redshaded counties indicate those from which Extension entomologists received reports of failures.

In response to the challenge that insecticide-resistant soybean aphids pose, we encourage growers, consultants and applicators to evaluate their soybean aphid management practices carefully. Best management practices include:

• Treat fields only when needed to reduce insecticide exposure to soybean aphids. This will reduce the selection pressure for further development of resistance.
  • Fields should be scouted on a regular schedule (every seven to 10 days).
     
  • Use the economic threshold (250 aphids per plant, with greater than 80 percent of plants infested) to determine when to apply insecticides.
     
  • Treat with in five to seven days of exceeding the economic threshold to protect yield.

• If a field exceeds the threshold, make sure the insecticide is applied correctly.

  • Use an effective (and labeled) insecticide at full labeled rate.

  • Use proper nozzles, spray volume (15 to 20 gallons per acre by ground; 3 to 5 gallons per acre by air) and pressure (40 pounds per square inch).

  • Spray under favorable environmental conditions to promote efficacy and reduce drift.

  • After applications, scout fields again after three to five days to ensure the product provided the level of management expected.

• If a field needs to be retreated due to a failure, rotate to a different insecticide group for the follow-up application. Tables 1 and 2 list insecticide groups, active ingredients and example trade names of products available for soybean aphid management.

  • Avoid applying a pyrethroid (Group 3A) insecticide as the first foliar application, especially if pyrethroid-resistent soybean aphids are common. Select an alternative insecticide group, such as sulfoxamine (Group 4C) or pyropenes (Group 9D).

  • On February 28, 2022, the U.S. Environmental Protection Agency (EPA) revoked all food tolerances for the insecticide chlorpyrifos (organophosphate, Group 1B). Growers are not allowed to apply chlorpyrifos on soybeans or any food or feed crop.

  • Mixtures of insecticides (premixes or formulated mixtures) may be effective for pest suppression but generally are not preferred for insecticide-resistance management.

  • Insecticide seed treatments are not a viable answer to managing insecticide resistant aphid populations.

Table 1. Foliar insecticides with a single active ingredient that are labeled for soybean aphid management.

Note: Insecticides labeled in different states can vary. Please check with your local state pesticide database for a current listing of insecticide products registered for soybean in your state. 

• Report suspected cases of insecticide-resistant soybean aphids to a local/regional Extension educator or Extension entomologist (see contact information on back). Before assuming resistance, try to rule out other potential causes for an insecticide failure (such as incorrect rate or application method, or unfavorable environmental conditions).

Until aphid-resistant soybean varieties and other management tactics become more widely available, cost-effective management of soybean aphid will continue to rely on scouting and threshold-based insecticide applications of the few labeled insecticide groups (Table 1).

This short list of insecticide groups is under threat of becoming even shorter through continued development of pest resistance to insecticides and potential regulatory actions. The agricultural community would be wise to work together to preserve the effectiveness of and continued access to these important tools for protection of crops from insect pests.

Factors that likely led to the development of insecticide resistance in soybean aphids:

• Frequent infestations – Economically threatening infestations of soybean aphid have occurred more frequently in portions of Minnesota and neighboring states than in other parts of the soybean aphid’s range, resulting in a long history of selection pressure for development of resistance.

• Limited number of insecticide groups for soybean aphid management (Table 1) – Management of soybean aphid has relied on foliar applications of only a few insecticide groups, mainly pyrethroids (Group 3A) and organophosphates (Group 1B), for more than 15 years.

• Misuse of insecticides can result in pests being exposed to insecticides more frequently, which further increases selection pressure. Examples of this include:

  • Application of insecticides when pest populations are below economic threshold.

  • Tank mixing insecticide with herbicide applications regardless of pest populations.

  • Applying insecticides below the labeled rate.

  • Repeated application of the same active ingredient or insecticide group within a single season.

Table 2. Foliar insecticides with two or more active ingredients (often called premixes or formulated mixtures) labeled for soybean aphid management. Mixtures may be effective for pest suppression, but generally not preferred for insecticide resistance management.

Note: Insecticides labeled in different states can vary. Please check with your local state pesticide database for a current listing of insecticide products registered for soybean in your state.

Photo Credit:

Photo courtesy of P. Beauzay, NDSU

• Minnesota: Robert Koch, University of Minnesota, email: koch0125@umn.edu, phone: 612-624-6771 www.extension.umn.edu/agriculture/soybean/pest
• Iowa: Erin Hodgson, Iowa State University, email: ewh@iastate.edu, phone: 515-294-2847 www.ent.iastate.edu/soybeanresearch/content/extension
• North Dakota: Janet Knodel, North Dakota State University, email: janet.knodel@ndsu.edu, phone: 701-231-7915 www.ndsu.edu/agriculture/ag-hub/ag-topics/crop-production/crops/soybeans
• South Dakota: Adam Varenhorst, South Dakota State University, email: adam.varenhorst@sdstate.edu, phone: 605-688-6854 http://igrow.org/up/resources/03-2007-2017.pdf

Insecticide options for resistant soybean aphids, University of Minnesota Extension. https://extension.umn.edu/soybean-pest-management/insecticide-options-resistant-soybean-aphid

North Dakota Field Crop Insect Management Guide. NDSU Extension Service, E1143 (revised). www.ndsu.edu/agriculture/sites/default/files/2022-01/Insect%20Management%20Guide%20E1143-22.pdf

South Dakota Pest Management Guide: Soybeans. South Dakota State University Extension and South Dakota Department of Agriculture. http://igrow.org/up/resources/03-3042-2017.pdf

Management Recommendations for Soybean Aphid (Hemiptera: Aphididae) in the United States. Journal of Integrated Pest Management. 3(1): 2012. http://dx.doi.org/10.1603/IPM11019

Biology and Economics of Recommendations for Insecticide-Based Management of Soybean Aphid. Plant Health Progress 17(4): 265-269. http://dx.doi.org/10.1094/PHP-RV-16-0061

Always read, understand and follow the Environmental Protection Agency-approved label directions on the product container.

Disclaimer: Insecticides are given as examples only and do not imply endorsement of one product versus another nor discrimination against any product not mentioned by the authors or the universities.