Identification of Late Season Corn Insects

Unlike the Western bean cutworm, corn earworms are cannibalistic so rarely is there more than one per ear. This species has a wide color variation from black to green (Figure 1). Usually more of a significant pest of sweet corn than field corn.

The aphid is blue-green, pear shaped, and wingless (Figure 2). It has short antennae and purple spot at the base of the cornicles. Usually first found in the whorls spreading to the tassel later in the season.

Depending on geography, late season corn can be infested with European corn borer larvae from the single generation type (Northern locations) or larvae from second generation of the two generation type (majority of Midwest) (Figure 5). Larvae can be found in the stalk, ear, and ear shank. Scout for insect frass (excrement) in leaf sheaths, holes in the stalk, shank, or ear. Feeding can reduce nutrient and water transfer, increase risk of stalk diseases, and stalk lodging.

The identifying characteristic for the fall armyworm larva is the white inverted Y-shape suture between the eyes (Figure 6). Moths are usually attracted to late developing corn or late planted corn as they do not overwinter in the Corn Growing Region and fly into the Midwest from the southern states.

Early season injury is usually confined to field margins, but as the majority become adults, movement into the field increases. Grasshoppers feed on leaves, silks, and ear tips, and when populations are very high, the entire plant can become stripped.

The Japanese beetle can clip silks and injure developing kernels at the tip of the ear. Like adult corn rootworms, the silk clipping is rarely of economic concern.

The larvae are dull with black spots in regular pattern along the body. Interestingly, the spots are not present on overwintering larvae. There are two to three generations per year with the first generation feeding on the growing point, resulting in “dead heart”. The second generation feeds in the stalk and girdles the stalk above the soil line. This injury can result in lodging.

The southern cornstalk borer larva is creamy yellow during the winter and white with black spots in the summer and very similar to the southwestern corn borer. It attacks primarily maize but also feeds on grain sorghum and sugarcane. There are usually two generations each year although three generations can occur. Injury is similar to the southwestern corn borer. Tunneling may be extensive in the lower portion of the stalk, primarily just above the soil line. disrupting nutrient and water uptake.

The western bean cutworm attacks the ear and can be identified by the brown bars behind the head (Figure 10/Figure 12). Typically, unlike corn earworm, more than one larva can be found in the ear.

The banks grass mite is most common in the western corn belt where low precipitation levels allow the population to expand rapidly. Banks grass mites are very small, about 1/32 inch in length. Their bodies are oval and vary from green to brown in color. They have eight legs and a row of dark spots, brown to reddish brown, on either side of the abdomen extending from near the head to the end of the abdomen (Figure 13). The number and position of the spots are one feature in distinguishing Banks grass mites and two-spotted spider mites.

The two spotted spider mite is more of an economic concern during hot dry weather, when populations can expand extremely quickly. Its host range includes a wide variety of plants, including corn.