- Agronomic: soybeans
- Education and Training: farmer to farmer, on-farm/ranch research
- Pest Management: chemical control, economic threshold, field monitoring/scouting, integrated pest management, precision herbicide use, weed ecology
Soybean aphid, an invasive species first reported in 2001, has become the most damaging insect pest of soybeans in the U.S. Organic growers in the north central states produce 65% of U.S. organic soybeans and have lost significant yield to this pest in recent years. Yield losses in NW MN were 40 to 50% during the 2006 and 2008 outbreaks. Currently, there are no successfully reliable OMRI approved control options for this insect. The threat from soybean aphids changes the economic sustainability of organic soybeans.
When soybean aphid infestations have occurred in organic systems, producers rely on preventative measures to decrease the likelihood of an infestation. Those measures occur naturally (e.g., predation, parasitization, fungal epizootics) and are largely encouraged through environmental conditions and not through direct management efforts by organic growers. Use of OMRI approved insecticides has been inadequate. Though there are larger long term studies that might improve the naturally occurring controls, the immediate need is to improve short term management options.
We propose to evaluate three strategies to determine whether they provide significant impact on aphid populations to protect yield in an organic system.
Planting Date and Relative Maturity (RM): Soybean aphids begin to colonize fields in late May. Infestations can reach serious economic levels by early July during outbreak years. In non-outbreak years, infestations may not reach economic levels until early August. Beginning flower (R1) to pod set (R4) are the most injury-susceptible stages. Organic soybeans are planted later, following multiple pre-plant tillage passes, to help with weed management. Delaying planting pushes plant development later and may result in greater aphid problems. Delaying planting also reduces yield potential. A planting date x RM interaction study will take a look at the impact on season long aphid populations, weed control, yield and quality.
Delaying Aphid Colonization with Reduced risk OMRI Approved Insecticide:
The OMRI approved insecticides, azadirachtin and insecticidal soap, have demonstrated some effect on soybean aphid in the laboratory, but their effectiveness is weak under field infestation conditions. This study proposes to evaluate the ability of multiple applications (late June to early August) of these compounds to delay aphid colonization on plants, reduce subsequent population peaks, and protect yield. The study would include documentation of beneficial insects (e.g., predators and parasites) and their numbers through the season.
Evaluate Pyganic® (natural pyrethrum) performance with Air-Assist Sprayer Technology: Preliminary work in 2009 has demonstrated that Pyganic when applied with an air-assist sprayer improved the performance of the insecticide and could reduce aphid infestations by 40 – 60%. This study would expand upon the preliminary work, increasing plot size with the intent of evaluating control at a lower treatment threshold and assessing the impact on yield, seed quality, and beneficial insects.