NPIPM:Billbugs on corn
Authors: Buyung Hadi, Robert Wright, R. Jeff Whitworth, Holly Davis, and J.P. Michaud
Corn billbugs are more abundant, and thus more of a problem, in the coastal plains of the southeastern US states. Nevertheless, billbugs can be found on corn in the central part of the US corn belt.
Identification
Billbugs are stout bodied snout beetles with adults measuring up to 0.5 in. or 1.3 cm long. Two species of billbugs are commonly found on corn: maize billbug, Sphenophorus maidis, and southern corn billbug, Sphenophorus callosus. Maize billbug adults are black with shiny ridges on the wing covers, while southern corn billbug adults are grey, dark brown or dull black in color. In the field, adults are often found covered in dried soil and are often overlooked during sampling. The eggs are white and kidney-shaped. Larvae are cream-colored, about 5/8 in (1.6 cm) long, and legless with brown heads.
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Life Cycle and Seasonal History
Billbugs overwinter as adults in the soil or plant litter near cornfields or in low-lying areas containing alternative hosts, such as nutsedges. The presence of yellow nutsedge in a field is commonly associated with increased damage by billbugs. The overwintered adult billbugs begin to become active about the time of corn emergence. These adults move to corn fields and start to feed on corn seedlings on the field border. Apart from corn, they may also feed on other alternative host plants such as sedges, rushes and grasses. Even though adult billbugs posses wings, movement primarily occurs by walking.
Females lay eggs in the base of corn stalks or in the soil around the plant. Hatching larvae bore into the base of the plant, feeding on the stalk. In the summer, pupae are formed in cells within the stalk or in the soil. New adults emerge in late summer and move to overwintering sites.
Plant Injury and Damage
In the spring, adult billbugs come out of overwintering sites and start to feed on corn seedlings. They feed on the lower stem, often leaving holes on unfolding leaves. Corn seedlings may die or tiller extensively in response of billbug feeding. As the plant grows, stems become larger and the significance of adult billbug feeding damage is progressively reduced. Injured plants are usually found on field border although in situations with large populations of billbugs, injuries due to billbug feeding may be found within the field. Only high levels of billbug population represent significant threats toward corn.
Management Approaches
Scouting and Threshold
Billbugs do not usually pose an imminent threat towards corn production in the Northern Plains. But if more than 5 percent of seedlings are lost due to billbugs feeding, postemergence insecticides are warranted. Spot treatment along field margins where the injuries are evident will reduce the usage of pesticides.
Cultural Methods
Crop rotation reduces billbug pressure in a given field. Management of alternative weedy hosts such as sedges will also reduce billbug populations. Early planting and promotion of rapid growth by ensuring proper fertility and pH maintenance, usage of rapid growing cultivars, tillage and application of starter fertilizers help the plants to quickly arrive at growth stages where billbug feeding does not incur much damage.
Other Online Resources
Radcliffe's IPM World Textbook, Maize insect pests in North America
Van Duyn, J.W. and R.J. Wright. 1999. Billbugs. In: Steffey, K.L. et al. (eds.) Handbook of corn insects. Entomological Society of America
