Billbugs: an early surprise

Billbugs are early-season seedling corn pests that seldom cause economic damage in Iowa. But billbugs can kill seedling plants and significantly reduce stands if their populations are large. Two reports during the week of May 19-23 substantiate the damage potential of these insects. Brad Buchanan, Crop Tech Services, reports 20 acres infested in a Keokuk County field. The billbugs were damaging 10-90 percent of the corn. Another infestation in Washington County, reported by Ken Reed, had billbugs reducing the plant population from 32,000 to 15,000 plants per acre.

Billbug species. These insects are weevils and three species are known to damage corn in Iowa: maize billbug, southern corn billbug and claycolored billbug. The maize billbug is 5/16-inch long and is the most common of the three species. The southern corn billbug and claycolored billbug are much larger, up to 3/4-inch, but are uncommon. All three species are characterized by a very hard body and a long, downward curved beak.

Billbug injury to seedling corn in the field
Billbug injury to seedling corn

Billbug injury. Billbugs injure corn two different ways. First, the adult weevils chew small holes into the stalk of seedling plants where they eat the tender leaves in the center. When the leaves emerge, they often wilt and are riddled with transverse rows of circular or linear holes. Plants may be killed. Those that live are stunted and deformed, often with twisted leaves and numerous tillers or suckers around the base of the stalk. Second, billbug larvae will tunnel in the base of the stalk, causing further stunting of the plant.

Claycolored billbug
Southern corn billbug

Billbug life history. Billbugs overwinter as adults. They seldom fly but may crawl 1/4-mile in search of food. They are most common in fields with nut sedge and they will feed on corn, especially in low, wet areas, About 200 eggs are laid in the spring over a two-month period. The larvae hatch in 4-15 days and then feed in the base of the stalk or the larger roots. The larvae are white, humpbacked, legless, with brown or orange heads. Larvae pupate in the soil or stalk. There is one generation a year. When startled, billbugs often play "possum" by falling to the ground and not moving for several minutes. This behavior, plus the fact that they are usually dusted with soil, makes them difficult to find when scouting in areas of billbug-damaged corn.

Billbug control. Several liquid insecticides are labeled for use in field corn, but only Lorsban 4E (2-3 pints/acre) lists billbugs on the label. Soil insecticides at planting may not be effective in controlling adult billbugs. Fields should be scouted for billbugs and their injury if nut sedge is a common weed in the field.

This article originally appeared on pages 79-80 of the IC-478(11) -- June 2, 1997 issue.

Updated 06/01/1997 - 1:00pm