University of Illinois

No. 17/July 18, 1997

Corn Leaf Aphid Densities Impressive in West-Central Illinois

Don Rhoads, a research agronomist with Burrus Hybrids, reported that many fields throughout west-central Illinois are heavily infested with corn leaf aphids. In several counties, concern over the potential economic impact of corn leaf aphids will escalate if dry conditions persist. Our threshold in commercial corn for corn leaf aphid control suggests that treatments may be warranted when at least half the corn plants in the early tassel stage have light to moderate infestations (50 to 400 aphids per plant) and plants are under drought stress. If soil moisture is adequate, a treatment may be warranted if there are more than 400 aphids per plant.

As indicated in an earlier issue of this Bulletin (no. 15), treatments for corn leaf aphids in seed-production fields, according to the Seed Corn Pest Management Manual for the Midwest (published by Purdue University), is "most effective 2 to 3 weeks prior to tasseling, after which, it is rarely advisable." The manual also provides the following information for the management of corn leaf aphids during pollen shed: Although control is not normally required once the tassels have emerged, on occasion aphids may interfere with pollination and treatment may be warranted. If aphids are sufficiently numerous to limit the flow of pollen, an insecticide may be needed. However, anthers and tassels covered with honeydew at the time of treatment will not benefit from the insecticideŠtreatment would only benefit plants with aphids, but not yet enough honeydew to limit the flow of pollen. Thus, the status of pollination and percent of plants with inhibited pollen flow should be carefully considered.

For additional information about corn leaf aphids, please refer to issue 15 of this Bulletin.

Mike Gray, Extension Entomology, (217)333-6652