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Turfgrass and Insects


Source: Lee Jenkins Collection, MUWallace C. Mitchell photoAdult billbugs are about 2/3 inch long. In some areas, maize billbugs are referred to as elephant bugs because they are gray-brown and have a snout reminiscent of an elephant's trunk.

Feeding by maize billbugs, Sphenophorus maidis Chittenden, can stunt or kill young corn plants.

Soon after they emerge as adults, the weevils insert their long snouts into the base of cornstalks and begin feeding. They cut a narrow feeding slit, usually below ground, up to 1/2 inch long in the side of the young stalk. Small plants may be stunted or even killed by billbug gouging and feeding. As leaves emerge from larger injured plants, a symmetrical row of holes appears across the leaves from billbug feeding that occurred while the leaves were still rolled. If feeding has injured the growing point, excessive suckering and distorted growth results. Legless billbug grubs feed inside the stems near the soil surface and may also cause stunting.

Leaf feeding does not result in economic injury to the crop. Control is warranted only if a significant number of plants are being injured by gouging of the inner stem and adults are still present. Treatments are not effective against grubs inside the stem. There are no economic thresholds established for billbug injury in Missouri.

Billbugs overwinter in grasses and sedges (especially yellow nutsedge), field residue, or soil. In the spring, billbugs feed, mate and lay up to 200 kidney-shaped eggs during a two-month period. The tiny grubs develop inside the stem of the young corn plant. Adults are often difficult to find, even around injured plants, because they blend in with the soil, and they are mostly active at night. Billbugs seldom fly, but they will crawl up to a 1/4 mile in search of food. There is one generation a year.

The best way to reduce the impact of billbugs on corn is to practice crop rotation. Plant corn the following year at least a 1/4-mile away from the previous cornfield.

Turf damage due to billbugs can be confused with damage caused by drought, disease, chinch bugs or white grubs. Symptoms of billbug injury are spotty, dead patches of turf that are easily pulled up, with the stems breaking off at the crown. In addition, the stems are hollowed out or filled with a light brown frass. The best time to control billbugs is in May to kill the overwintering adults before egg laying begins.

Wild thing

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IPM1020 Turfgrass and Insects | Page 6 | University of Missouri Extension