Catch-All Report: Other "Bugs" in Corn

July 2, 1999

· Corn earworm larvae have been found in ragged whorls of corn in some fields.

· Grasshopper nymphs are emerging from noncrop areas.

· Stink bug injury is still noticeable in no-till cornfields in western Illinois.

Instead of writing full-fledged articles on all of the observations people have made, I thought I'd summarize some of their findings in this "catch-all" article. These are simply "heads-up" notes to make you aware of some of the insects you might encounter as you continue scouting in cornfields.

Corn earworm larva.

A few people have observed young corn earworms causing noticeable injury to whorl leaves in some cornfields. Although we usually associate corn earworms with the damage they cause to corn ears (especially seed and sweet corn), they also can cause injury that resembles leaf feeding by fall armyworms. Injured leaves are very ragged, and considerable messy frass (excrement and bits of plant material) can be found in the whorls. Upon closer inspection, you might find a rather striking corn earworm larva. Newly hatched larvae are translucent cream to white with a black head. Larger larvae vary from yellow, brown, and red to green with prominent bands of cream, pink, green, or yellow. The head usually is dark yellow or orange. The cuticle is covered with microspines. Take note of their presence, but don't overreact. Corn earworms rarely cause enough defoliation injury in the Corn Belt to warrant control in commercial field corn.

Grasshopper nymphs are appearing in "egg beds" around crop fields. "Egg beds" are noncrop areas such as ditch banks and grass waterways in which female grasshoppers deposited eggs last fall. It is time for the young grasshoppers to become more noticeable, so keep your eyes open, especially as you walk into and out of fields of corn and soybeans. Report significant numbers to us so that we can share your observations with others.

Brown stink bug adult.

Stink bug injury to corn plant.

Suckering of corn plant caused by stink bug injury.

Mike Roegge, Extension Unit Educator/Crop Systems in Quincy, has observed several fields of no-till corn in western Illinois in which stink bugs caused significant injury. In corn well over knee high, Mike is still finding stink bug adults and nymphs in the whorls of the corn plants. The damage was so severe in one field that treatment has been recommended, although treatment at this time of year may not help much. Plants damaged earlier this spring are stunted, and many have produced suckers. Severe injury has resulted in development of necrotic tissue while the leaves were wrapped up in the whorls. Thresholds for stink bugs in corn have not been developed, so decisions to treat them are based solely on gut feelings. I am guessing that the mild winter weather favored survival of stink bugs.--Kevin Steffey

Author: Kevin Steffey