During the past week, a few reports of billbugs began to trickle into our offices. And as I indicated in the article "Report from the Field," I observed a little billbug injury in a cornfield in which nutsedge was fairly common. Although not all fields infested with billbugs are also infested with nutsedge, or vice versa, the probability of both occurring in the same field is pretty good. |
Billbug adult on seedling corn plant.
Billbugs overwinter as adults in protected areas around cultivated fields. The adult is about 1/4 to 1/2 inch long, gray, dark brown, or black (depending on the species) with a prominent "snout." In the spring, the adults walk to either corn seedlings or nutsedge to feed, after which the adults mate and females lay eggs either in the soil or in cavities eaten into plant stems. After hatching, billbug larvae also may damage corn, but information about this type of injury is limited.
Tillering of corn plants caused by billbug damage.
Adult billbugs feed on the lower stems of corn seedlings, often injuring or killing the growing point. Small plants may die or tiller extensively. Another characteristic symptom of billbug injury is rows of oblong holes in expanded leaves. Damage usually is most severe along field edges but sometimes is spread throughout the field.
There are no established economic thresholds for billbugs in the Corn Belt. In the southeastern United States, entomologists suggest that an insecticide may be warranted if 5% or more of the seedlings are lost. If injury is confined to field margins, spot treatments are appropriate. The only insecticide suggested for control of billbugs is Lorsban 4E at 2 to 3 pints per acre. The label suggests that you apply Lorsban 4E in 20 to 40 gallons of finished spray per acre, and only with ground equipment.--Kevin Steffey