The bad news is that corn aphids are plentiful this summer, stealing the spotlight from other more common insect pests, at least temporarily. Because they can swarm a plant and make it almost black with aphids, they are difficult to miss. The good news, though, is that unless you raise seed corn or are in a special situation, aphids likely won’t cause economic damage.

Here is what Nick Seiter, Extension field crops specialist at the University of Illinois, reported in the Illinois Bulletin, July 26 edition, published by Farmdoc. “I have had many reports of corn leaf aphids over the last couple of weeks, including several in pretassel corn,” he said.

Corn leaf aphids are usually found inside the upper whorl and are darker in color than other species, Seiter said. Most other species are found on the undersides of leaves.

“This year, the wide variety of planting dates has resulted in corn that is all over the place in terms of stage of growth,” he explained. “These aphids are particularly a problem if they are present in large numbers during pollination. Fortunately, where we have adequate moisture and cool temperatures during pollination, this effect will be minimized.”

Seiter suggested considering an insecticide if 50% of plants have aphid colonies, or about 50 to 100 aphids, prior to or during R1. Once pollination has passed, it takes much greater numbers to cause yield loss, he noted.

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Why people spot aphids

Steve Gauck, a regional agronomy manager for Beck’s, based near Greensburg, Ind., also has received calls about aphids in his area. While corn aphid numbers could be up, he believes part of the issue is that they concentrate on individual plants, so people are noticing them.

“Planting dates were really spread out here too, and there was a wide range in pollination timing,” Gauck says. “These aphids are attracted to fresh plants, especially those pollinating, and they can be attracted to individual plants in big numbers. When that happens, they’re easy to spot, and the problem may seem worse than it is.”

According to the Purdue University Corn and Soybean Field Guide, corn aphids are very small, greenish to reddish, globular shaped, and winged or wingless. They’re usually more of a concern on drought-stressed plants but can interfere with pollination in rare cases.

While pollination troubles due to aphids may be rare in commercial fields, Darin Lucas, a production manager with Beck’s, based at Atlanta, Ind., says it’s not so rare in seed fields. In fact, it’s a concern every year, and definitely this year. Many seed fields were sprayed with insecticides for these pests.

“They create a sticky substance in tassels that can interfere with pollen shed,” he notes. “In seed production fields, we need inbreds to shed as much pollen as possible. So, if something interferes with pollination, we become concerned and act, if necessary.”

Fortunately, aphids do have natural enemies — other insects and even diseases. In commercial fields, these enemies are often sufficient to prevent corn aphids from causing economic damage.