This is becoming an “interesting” year for soybean aphid management. After a couple years of limited infestations due to drought, soybean aphid infestations are widespread in 2024.
Be thorough when scouting. Aphids are likely distributed throughout the height of the canopy (not just on upper leaves), so examine entire plants.
Weekly scouting of fields is often recommended, but more frequent scouting may be needed as forecasted weather conditions will be favorable for aphid population growth.
Under typical field conditions, the time required for population size to double has been estimated at six to seven days. However, aphid populations can double in as little as a few days under more ideal conditions, with temperatures in the upper-70s to mid-80s.
Scouting thresholds
Use the threshold of 250 aphids per plant (with 80% or more of the plants infested and with aphid populations increasing) to determine when to treat a field with insecticides.
This threshold is not when damage occurs to the plant, but indicates the aphids will likely continue to increase and reach economically damaging levels. Therefore, this threshold is the trigger point when an insecticide application should be lined up within seven days to prevent the population from reaching a damaging level.
Infestations of fewer than 250 aphids per plant are less likely to continue to increase to damaging levels, so an application may be unnecessary (less likelihood of return on investment). Continue scouting those fields, and let the natural enemies like predators, parasitic wasps and fungal diseases take their toll on the aphids before using an insecticide.
Remember retail profits, not science, may be driving lower threshold recommendations.
If you need to apply an insecticide for soybean aphids, think critically about what product to use. Avoid products containing only a single pyrethroid or multiple pyrethroids because of widespread pyrethroid resistance.
Some chlorpyrifos-containing products are available again. These are effective, but keep in mind that the human safety profile for organophosphates is worse than some of the other products. As a broad-spectrum insecticide, chlorpyrifos will kill soybean aphids and natural enemies alike.
There are many formulated mixtures available, but are mixtures really needed? Aphids are likely the only threatening insect pest in most fields, so why add a broad-spectrum insecticide like a pyrethroid to one of the newer, more aphid-specific insecticides like sulfoxaflor (Transform) or afidopyropen (Sefina)?
Those newer insecticides (Transform, Sefina and Sivanto) are effective against aphids on their own and are less toxic to natural enemies (e.g., lady beetles, etc.), which is a great bonus feature, but price points will need to be taken into consideration.
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