Corn Leaf Aphids

Corn leaf aphids are small insects with legs that are usually blue-green in color, similar in appearance to soybean aphids. They feed by piercing the corn plant and sucking nutrients from the phloem. In the Midwest, they usually arrive and complete their feeding sometime in July. Corn leaf aphids tend to congregate near the ear on the plant, and as they build up in population, can cover the ear leaf, lower stalk and tassel (Figures 1 and 2).

Figure 1 Figure 1. Dust and residue sticking to aphid honeydew can reduce photosynthesis.
Corn leaf aphids on ear leaf Figure 2. Corn leaf aphids on ear leaf.

In the past few years, aphid populations have appeared to be larger and occurring later in the season. As the population builds, the sticky ooze that aphids excrete (honeydew) may interfere with pollination and photosynthesis. The sticky ooze on tassels can prevent the release of pollen into the air and when on silks, can prevent fertilization. Leaves that are covered with the ooze capture dust and other contaminants that can reduce light interception and energy production through photosynthesis.

Even large populations rarely result in any large amount of yield loss. While currently no formal economic threshold exists in the Midwest for treating corn leaf aphids, a general recommendation suggests that a treatment may be warranted if 50% of plants have more than 100 aphids, especially if plants are under moisture stress. Insecticides applied when the aphids are deep in the whorl are likely to be noneffective. Lady beetles and lacewings are natural enemies of aphids and when present, can be a natural control. Additionally, parasites are known to “feed” on aphids, leaving behind parasitized mummies. The presence of mummies is another indication that aphids are being controlled naturally.

Brent Brekke

Technical Agronomist

Source:

Hodgson, E. 2016. Managing aphids in corn. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/.
Hodgson, E. 2009. Scout for corn leaf aphids before tasseling. Integrated Crop Management. Iowa State University. https://crops.extension.iastate.edu/.

Web sources verified 6/28/19.

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