MINNEAPOLIS — Soybean aphids can now be found in some soybean fields, particularly in fields where soybeans were planted early. Generally, both the percent of plants infested and the average number of aphids per plant remain low. It is too early to know what will come of these soybean aphid infestations for 2019. However, if fields reach treatable levels this year, there are now two additional insecticides available for soybean aphid management. A new insecticide, afidopyropen (Group 9D) (Sefina from BASF) received registration for use in soybean last fall. In addition, sulfoxaflor (Group 4C) (Transform from Corteva) recently regained registration for use in soybean (EPA decision). These products are a welcome addition to the list of insecticides available for soybean aphid management (see table below). Both afidopyropen and sulfoxaflor have proven effective against soybean aphid in our research trials. Unlike the pyrethroids (Group 3A) and organophosphates (Group 1B) often used for soybean aphid, afidopyropen and sulfoxaflor, in addition to flupyradifurone (Group 4D) (Sivanto from Bayer), are generally less toxic to the beneficial predatory insects in our crops and can be a better fit for integrated pest management (IPM) programs. However, keep in mind that the reduced spectrum of these products could limit efficacy against other pests. Please read and follow label instructions for products.
Soybean aphid populations resistant to pyrethroid insecticides have been found in Minnesota since 2015 and are likely still present. The recent availability of afidopyropen and sulfoxaflor will provide more flexibility for insecticide alternations for insecticide resistance management. However, sulfoxaflor (4C) and flupyradifurone (4D) are separate subgroups within the same insecticide group as the neonicotinoids (thiamethoxam, imidacloprid, clothianidin) (Group 4A) used in seed treatments. Use of these Group 4 foliar insecticides on aphid populations exposed to neonicotinoid seed-treated soybean could provide additional selection pressure for resistance development. In addition, keep in mind that some of the formulated mixtures of foliar insecticides include neonicotinoids. If soybean fields need to be retreated for soybean aphid, try to use an insecticide from a different effective insecticide group. Please inform us if you experience an insecticide failure for soybean aphid management and suspect insecticide resistance.
You should now be scouting your soybean fields for soybean aphid (Scouting for Soybean Aphid). Use the threshold of an average of 250 aphids per plant (with 80% or more of the plants infested and aphid populations increasing) to determine when to apply insecticides for soybean aphid. Remember that this threshold is the point at which you should line up an insecticide application to keep the infestation from increasing to an economically damaging level.
Table: Insecticides available for soybean aphid management. Insecticides are given as examples only and do not imply endorsement of one insecticide versus another nor discrimination against any insecticide not mentioned by the authors.
— Robert Koch, University of Minnesota Extension Entomologist and Bruce Potter, IPM Specialist
For more news from Minnesota, click here.