Billbugs as Pests of Field Corn
Of the several species of billbugs that feed on corn plants, only Sphenophorus aequalis aequalis Gylential is of economic concern in Pennsylvania. The maize billbug and the curlew-bug, destructive species to corn in the Midwest and South, are scarce in Pennsylvania.
The principal host for claycolored billbugs is nutsedge but adults will feed on corn plants. Billbug larvae cannot develop in corn; thus, damage is limited to those fields where nutsedge was a problem the previous year. Damage that does occur is usually confined to a few scattered fields.
The adult beetle is about 3/8-inch long with a pronounced beak. Billbugs usually are covered with a thin coating of soil particles, giving them a reddish-brown color, hence the name claycolored. When this coating is removed the body has a bluish-gray on the thorax.
With her beak, the female gouges a small hole into the plant stem and deposits a tiny, white kidney-shaped egg. Eggs hatch in about 10 days. The minute white, chunky, legless grubs are somewhat humpbacked with yellowish-brown heads. The larvae feed inside the plant stems and nutlets for about 3 weeks and are about 1/4-inch long when mature. The naked, white pupae may be found in the stems or in pupal cells among the roots.
Billbugs overwinter as adult weevils in the soil. They emerge during May and feed on various kinds of grass plants. After mating, each female deposits about 200 eggs in stems of nutsedge plants. This takes place over a period of several months.
The grubs or larvae feed and develop in the stems and underground nutlets of the host plant. They reach maturity in late June and July and pupate in the soil. The pupae transform into adult weevils by autumn. A few emerge in the fall, but most remain in the soil until the following spring. There is one generation per year.
Most feeding and damage to corn plants occurs during May. Upon emergence from the soil, the adults chew small cavities in the stems. Numerous stem punctures can severely retard or even kill small plants. As the plant grows and the leaves unfold, typical billbug damage will show up as a series of 3 or 4 round holes across the leaf.
Fortunately, several of the more destructive species of billbugs are not abundant in Pennsylvania. For the predominant claycolored billbug, elimination of nutsedge from the field a year prior to planting corn will prevent damage. It is questionable if special insecticide applications are warrented to control billbugs. However, in those fields where billbugs may be a chronic problem, several soil insecticides are registered for this purpose. They should be applied over the row at planting. These insecticide labels can be checked by your farm supply dealer.
Check the Agronomy Guide or consult with your pesticide supplier or county agent for details of pesticide use.
Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.
Authored by: Stanley G. Gesell, Extension Entomologist, 1983
Dennis Calvin, Professor
April 14, 2000
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