University of Illinois

No. 10/May 30, 1997

Billbug Injury Reported in Southwestern Illinois

We have had a few reports that some cornfields in southwestern Illinois are infested with billbugs. The presence of billbugs in some cornfields may create confusion with suspected black cutworm problems. Fields most at risk are ones in which yellow nutsedge has become an established weed. Bluegrass and other species of grass also may serve as hosts.

There are several species of billbugs, but the maize billbug is the most common. Adults are gray, brown, or nearly black "snout" beetles from 2/5- to 3/5-inch long. Billbugs have chewing mouthparts at the end of a prominent snout. Adult billbugs are rarely seen because they blend with the soil and are active only at night (Figure 1).

Figure 1. Billbug adult.

The grubs are off-white with a brown or yellow-brown head. They are legless and humpbacked, shaped much like a kidney bean.

Billbugs overwinter as adults in the soil, grass, or litter and become active as corn begins to emerge in the spring. The beetles crawl into nearby fields and begin feeding at the base of the stalk, gouging small holes in the stem. Small plants may be killed, whereas older plants may have only transverse rows of holes in emerging leaves. However, if their feeding affects the growing point, distorted growth and excessive suckering may occur.

The adults lay their eggs in the gouged-out holes in the stems. Developing larvae that feed inside corn stems may also cause some injury. Later in the season, the larvae may drop from the stem and resume feeding on the roots. Pupation takes place either in the stem or in the soil. The life cycle requires several months for completion, and there is only one generation per year. Billbugs usually cause no economic damage to corn. Control is warranted only if a significant number of plants are killed or if their growth is affected. Leaf feeding is not economic. Lorsban 4E at 2 to 3 pints per acre will control billbug adults. For best results, use only ground equipment and apply 20 to 40 gallons of finished spray per acre.

Mike Gray and Kevin Steffey, Extension Entomology, (217)333-6651