Integrating Host-Plant Resistance and Insecticides for Sustainable Soybean Aphid Management

View the project final report

• 2014 annual report

Commodities

• Agronomic: soybeans

Practices

• Education and Training: extension
• Natural Resources/Environment: biodiversity
• Pest Management: biological control, botanical pesticides, chemical control, economic threshold, field monitoring/scouting, genetic resistance, integrated pest management
• Sustainable Communities: sustainability measures

Soybean aphid (Aphis glycines Matsumura) is a major pest of soybean in the Midwest. Insecticides, such as pyrethroids and organophosphates, are used to suppress soybean aphid outbreaks to prevent yield loss. Another management tactic is host-plant resistance. Genes have been found that confer resistance to soybean aphid (i.e, Rag1 and Rag2), and are available individually or combined in commercial varieties of soybean. However, aphid populations on aphid-resistant soybean plants can still build to economically damaging levels, which require treatment with insecticides to protect yields. In situations where resistant soybean needs to be treated with insecticides, reduced aphid population growth rates on the aphid-resistant soybean might allow for the use of less toxic insecticides (or rates of insecticides) that typically would be less effective against soybean aphid on susceptible soybean, and would be more compatible with natural enemies of the soybean aphid. Pest-resistant plants of other species are known to increase the susceptibility of insect pests to insecticides when the pests feed on those plants. If the use of resistant plants can allow for the use of less insecticide, or less toxic insecticides, there are several potential long-term outcomes for farmers. Operating costs may decrease due to less pesticide use. There may also be fewer non-target effects on beneficial insect populations, which reduce soybean aphid population densities. Environmental and human-health risks may decrease with decreased insecticide exposure. Finally, organic farmers may gain an effective combination of tactics for managing soybean aphid with organic-approved insecticides (e.g., Pyganic) used on aphid-resistant soybean. To evaluate the interaction between host-plant resistance and insecticides for soybean aphid management, we are proposing a greenhouse study and field study. Under controlled conditions of the greenhouse, we will quantify differences in susceptibility of soybean aphid to organic-approved and conventional insecticides when reared on aphid-susceptible and aphid-resistant lines. Under more natural field conditions, we will measure soybean aphid population growth rates on aphid-susceptible and aphid-resistant soybean lines before and after treatment with different insecticides. Soybean aphid populations will be established on all soybean lines and each line will be treated with a labeled rate of Pyganic, labeled or reduced rates of a pyrethroid, or remain untreated. We hypothesize that less toxic insecticides (or rates of insecticides) will maintain aphid populations below the economic injury level on aphid-resistant soybean, but not on susceptible soybean, which could increase compatibility of these tactics with natural enemies and increase sustainability of soybean aphid management.

Short term outcomes for this project primarily include changes in awareness of more sustainable pest management tactics for the soybean aphid and the integration of host plant resistance and chemical and biological controls. Farmers will benefit from becoming more aware that aphid resistant varieties are available and that overuse of pesticides may result in reducing beneficial insect populations.

If we show that less toxic pesticides can be used for suppression of soybean aphid outbreaks on aphid-resistant plants, our intermediate outcome is for farmers to begin adopting a management approach consisting of aphid-resistant plants and use of insecticides more compatible with biological control, or at the very least consider adoption if resistant varieties are offered in their geographic area that would suit their needs. Implementation of this practice could result in more sustainable soybean production with less reliance on insecticides through integration of multiple management tactics. Non-target effects of insecticides on natural enemies may also be reduced.

Since changes in growing practices may take time to implement, many of our potential outcomes are long-term. If demand increases for aphid-resistant varieties, seed growers may develop a larger selection of varieties with combinations of resistance traits, and give farmers more seed choices. Beneficial insect populations may also increase in soybean fields that previously had been treated with toxic levels of insecticides. Farmers may see decreased insecticide costs and increased yields from decreased aphid pressure. There may also be less persistence of insecticides in the environment and increased safety for farmers and applicators.