No. 14 Article 6/June 24, 2005

Corn Leaf Aphids

Corn leaf aphids are migratory insects that make their way into Illinois cornfields in the spring. Often, these insects go unnoticed until populations reach very high levels. Ria Barrido, Syngenta Crop Protection, reported finding corn leaf aphids in corn whorls in Champaign County on June 20.

These blue-green aphids start colonies in the whorls of corn plants. They remain in corn whorls until tassels emerge. At that time, aphids move down the plant, forming colonies on stalks and leaves and behind corn ears. Most years, populations are kept in check by natural enemies, such as lady beetles, lacewing larvae, syrphid fly maggots, and other insect predators. However, during hot, dry summers or when predators are scarce, populations can increase dramatically.

Corn leaf aphids (University of Illinois).

During the growing season, both adults and nymphs feed in the whorl, causing injury by removing water and nutrients. Damage is most severe between the late-whorl and pollination stages. Corn plants heavily infested with corn leaf aphids may wilt, curl, and show yellow discoloration. Tassels and silks may become covered with honeydew and turn sooty black as mold grows on them. If corn plants have adequate moisture, corn leaf aphids cause little damage. Stress caused by high densities of aphids is more severe during times when moisture is lacking for plants. Injury caused by the corn leaf aphid may exaggerate symptoms of drought stress.

As warm temperatures and lack of moisture continue around the state, please be aware of this insect in your cornfields and the potential for it to affect pollination.--Kelly Cook

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