Stop Billbugs From Stalking Your Corn Crop

Stop Billbugs From Stalking Your Corn Crop

Corn billbug

Here’s an extreme up-close look at a corn billbug.
Photo by Anyi Mazo-Vargas

Several species of billbugs attack corn. The two most likely billbugs in Florida are the maize billbug (Sphenophorus maidis) and the southern corn billbug (Sphenophorus callosus). Severe infestations can reduce yields up to 40%.

Identification
Larvae of maize and southern corn billbugs feed in corn stems. Other species attack corn only as adults. Most damage results from adult feeding. Corn becomes less sensitive to damage with age. Several species attack corn, but the maize billbug causes the most damage. Adults feed near the growing point, eating holes in developing leaves that results in rows of narrow slots in emerging leaves.

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Maize billbugs also may attack seedling corn at the plant base or just below soil level. They use their long beaks to feed on the inner portion of the stalk. Damage to the base of the plants causes the plant to send out numerous suckers, which usually do not produce marketable ears. Stalk damage causes breakage and reduced yield due to limited nutrients getting to ears.

Billbugs are weevils. The heads of both species are prolonged in front of their eyes into a long, downward curving, narrow snout. Maize billbugs are 3/8 inches to 9/16 inches long with a reddish-brown to gray base color and longitudinal shiny black lines on pronotum and wing covers. Lines on the elytra are less linear than on the abdomen. The head and legs are mostly shiny black.

Southern corn billbugs are 3/8 inches long and brown with golden reflections. Elevated bumps on pronotum and elytra are shiny black. The elytra have prominent dents at the base and humps near the end. The larva are legless, ivory-colored, soft-bodied grubs with harder yellow or brown heads that tunnel within the stalk before feeding down into the roots. Development takes several weeks.

Both species pupate within the base of the plant or tap root below soil level.

Survival and Spread
Adults need corn or yellow nutsedge to reproduce, but larvae can only complete development on corn.

Damage is often most severe in yellow nutsedge-infested fields or in border rows adjacent to this weed.

Kidney-shaped, white eggs are deposited in feeding punctures in corn stalk near the plant base. Larvae emerge in four to 15 days. Generation time is approximately 10 weeks.

Billbugs overwinter in the base of corn stalks and in field margins.

Management Methods
Billbugs are more likely to be a problem on poorly drained, organic soils and in corn-after-corn fields.

No-till production allows the pest to build up, while cultivation and pesticides reduce populations.

One of the most effective cultural tactics for reducing billbugs is crop rotation because adult corn billbugs walk rather than fly. Most of the pesticides labeled for billbug control are applied in the soil at planting.

Post-emergence rescue treatments may be used with fair success if fields are scouted shortly after corn emerges.

Consult UF/IFAS recommendations for formulations, rates, and pre-harvest intervals of currently labeled insecticides for billbug control in field corn and sweet corn in Florida.

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