By John Tooker
At this time of year it is unlikely that managing these aphid populations will be economical, and there would be a further challenge of getting effective control given the size of the plants and getting material through the canopy down to the aphids. The point of this article, then, is to learn from this issue, so the problem can be avoided in future years.
Over the past few weeks, we have heard of growers suffering from really large populations of corn leaf aphid in their corn fields (Figure 1). This pest is not hard to diagnose; if you have the problem, you can find thousands of aphids per plant and lots of sticky material on surrounding leaves. This sticky stuff is honeydew, which is the sugary, liquid excrement of aphids; this sugary snack often draws in wasps and other insects looking for a treat. To complicate matters, when honeydew lands on leaves, it is often colonized by sooty mold, which turns leaves black.
It so happens that these fields that have the aphid outbreaks are fields that received a fungicide application mid-season and the growers elected to throw a preventative insecticide application in with the fungicide. As preventative applications, these insecticides are not usually targeting any particular pests, and often end up doing more harm than good. The insecticide is particularly hard on the beneficial insects in the field, particularly lady beetles and their larvae and predaceous bugs. With these predators out of the way, small, often unnoticed aphid populations are able to grow unchecked into really big, ugly populations like those seen in Figure 1.
The best strategy for avoid this problem, and managing pests in general, continues to be Integrate Pest Management, which dictates that one only apply an pesticide when the pest population exceeds an economic threshold. To determine whether pest populations are large enough to warrant an insecticide spray, scout your fields! If the insect populations exceed thresholds, apply an insecticide; if not, don’t. It should be that simple.