Identification of Late Season Corn Insects

September 13, 2021

Late season insect infestations can be impacted by corn maturity. Particularly, corn that is planted late or maturing later than surrounding fields. Later planted fields are very attractive to females of the second-generation corn borers, corn earworms, and fall armyworms as green silks are preferred oviposition sites. Additionally, corn rootworm adults also prefer green silks or pollinating corn and these fields can become ovipositional sites that may result in significant injury the following season.

Table 1. Late season corn pests, VT to R6.

Click on the tab to identify Late Season Corn Insect Pests, VT to R6
Corn Earworm
Figure 1. Corn earworm. Picture courtesy of R.L. Croissant,

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.

Corn leaf aphid
Figure 2. Corn leaf aphid. Picture courtesy of Eric Burkness,

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.

European corn borer.
Figure 5. European corn borer. Picture courtesy of Frank Peairs, Colorado State University,

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.

Figure 6. Fall Armyworm. Picture courtesy of Frank Peairs, Colorado State University,
Figure 6. Fall Armyworm. Picture courtesy of Frank Peairs, Colorado State University,

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.

Two-striped grasshopper
Figure 7. Two-striped grasshopper. Picture courtesy of Whitney Cranshaw, Colorado State University,

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.

Japanese beetle
Figure 8. Japanese beetle. Picture courtesy of Whitney Cranshaw, Colorado State University,

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.

Southwestern corn borer
Figure 9. Southwestern corn borer. Picture courtesy of Frank Peairs, Colorado State University,

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.

Southern corn stalk borer.
Figure 10. Southern cornstalk borer. Picture courtesy of Clemson University – USDA Cooperative Extension Slide Series,

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.

Western bean cutworm on ear tip.
Figure 12. Western bean cutworm. Picture courtesy of Mike Weiss.

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.

Banks grass mite
Figure 13. Banks grass mite. Picture courtesy of Frank Peairs, Colorado State University,

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.

Two spotted spider mite females.
Figure 14. Two spotted spider mite. Picture courtesy of Frank Peairs, Colorado State University,

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.