|Soybean aphid biological control|
Your Soybean Checkoff.
Soybean aphid insecticides
Well-timed, foliar application of a labeled insecticide will reduce aphid populations and protect yield.
|Soybean aphid-infested leaf.
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Photo credit: Thelma Heidel-Baker
When to treat
Consider spraying when soybean aphid reaches the economic threshold of 250 per plant. Most of the plants should be infested (>80%) and numbers should be increasing. It’s an established, robust threshold developed using multiple years of data from multiple states in the Midwest. The 250 threshold provides five to seven days lead time to take action before high aphid densities start to reduce yield.
Do not adjust the 250 threshold down. It was created in the presence of damage by other insects, like Japanese and bean leaf beetles. It was created with data taken during the biggest aphid outbreak years (2003, 2005), so it doesn’t have to be modified because it’s a “big aphid year.”
Most critical, 250 is below the damage boundary – the lowest point where we can measure a yield loss. Experience shows that about 650 aphids per plant are needed before yield loss can even be detected by a yield monitor or in research trials.
Recognize there are a lot of beneficial insects out there, both predators and parasitoids. Spraying kills all of these. Scouting is important to catch those situations where predators and parasites clean up fields where aphids were beginning to build.
Do NOT add insecticides to fungicide or herbicide sprays unless aphid populations have reached the economic threshold. Applying insecticides as an insurance or prophylactic spray is not an appropriate IPM approach, and could cause a greater problem when the winged aphids arrive later in the summer.
Choosing an insecticide
If you do decide to treat, use a full rate of a labeled insecticide. Pyrethroids (e.g., Warrior II, Mustang Max, Asana, Baythroid) have a long residual, and work best at temperatures below 90°F. Organophosphates (e.g., Lorsban) have a fuming action, and may work well in heavy canopies or at high temperatures.
Do not use half rates and or a concoction of multiple products. Hit the aphids hard and only when exceeding the economic threshold of 250 per plant.
Maximize coverage in pressure and gallons per acre. A proportion of the aphid population is already on the lowest leaves of the plant and those aphids are hard to reach unless coverage is good.
| A summary of integrated pest management (IPM) tactics for soybean aphid are discussed, including cultural, genetic, economic, and chemical controls can be found in the recent publication Management Recommendations for Soybean Aphid in the United States. Hodgson, E. W. et al.
Soybean aphid outbreak in Michigan’s Thumb region - July 2013 by Christina DiFonzo, Michigan State University Extension, Department of Entomology
Management Recommendations for Soybean Aphid in the United States (2102). Hodgson, E. W. et al.
Journal of Integrated Pest Management (pdf)
Economic Threshold for Soybean Aphid (2007) Journal of Economic Entomology 100: 1258-1276 (pdf).