, Farm Journal Seeds & Production Editor
Say aphids and most Midwestern growers are programmed to think soybeans. Truth is, there are more than 4000 different aphid species. Now some of them appear to be headed to the cornfield.
Iowa State University entomologist Erin Hodgson says reports of aphids feeding on lower corn leaves started emerging in early August. "Corn leaf aphid thresholds are set for prior to tasseling, but we're getting some reports of aphids moving down the plant and forming colonies on the stalk,” she notes.
Cool temperatures through July may have contributed. Hodgson says moderate temperatures (between 70 to 80 degrees) favor most aphids for their maximum reproductive growth. Temperatures above 90 slow down aphid development.
"Some growers are scheduling sprays to prevent loss because numbers are still increasing and honeydew/sooty mold is showing up above the ear leaf,” she says. "I think aphids are becoming a more common problem in corn. Typically numbers decrease after tasseling and sprays are not needed.”
Hodgson says there are two different kinds of aphids that are typically found in corn this time of year, but that identification isn't all that critical to management.
In general, aphids are soft-bodied and pear shaped insects with walking legs. Hodgson says the main diagnostic feature of aphids is two small "tailpipes” toward the end of the abdomen. Like their soybean counterparts, aphids in corn also use their stylet to pierce and suck on the plant's phloem.
Corn leaf aphids are more rectangular or boxy in shape and actually prefer sorghum, but will feed on corn, barley, millet and many grasses. Bird cherry-oat aphid prefer wheat, barley, oats and rye, but can also be found in corn. Their bodies are more pear shaped.