ST. PAUL -- You may be planning or have been encouraged to apply an insecticide with an upcoming glyphosate application without regard for aphid populations. While this strategy may occasionally work, several problems can arise.
Cost: There is no data to suggest very low aphid populations hurt yield. Early applications are more likely to be re-colonized and require re-treatment. Claims of insecticide residual activity lasting a month, or longer, have little factual basis, particularly when applications are made to rapidly growing soybeans.
Resistance: The more often soybean aphids are exposed to insecticide the more quickly insecticide resistant populations will develop. More than one product could lose effectiveness at once, depending on the mode of resistance. An unpleasant wrinkle to soybean management would be aphids that won't die.
Increasing populations of soybean aphid, or other arthropod pests (such as spider mites) by removal of beneficial species: Removal of predators and parasites can have unexpected consequences. Imagine how quickly newly arrived aphids reproduce when you've removed the beneficials for them. When we do this with cages that exclude predators, aphid populations go from 10 to more than 1,000 in a little more than a week.
Compromises leading to poor insect and/or weed control: Ideal nozzle, water volume and pressure selection for insecticide and glyphosate applications are not the same. Herbicide and insecticide timings should be based on when to apply to the target pest (weed or aphid) to be most successful.
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There are potential shortterm and long-term risks when insecticide applications are made without regard to pest populations.
