Wireworm Baits and Preplant Decisions for Corn

Published: March 28, 2008

Wireworm is a group of insects which are often difficult to scout and manage. One method used to determine wireworm numbers prior to planting is the use of a solar baiting system. It can effectively estimate wireworm larval populations present at a site.

Wireworm on corn in Honduras. Frank Peairs, Colorado State University, Bugwood.org

The scouting technique consists of placing bait stations or traps at several locations within a crop field. A minimum of two bait stations per acre is recommended, but in reality establishing 5 to 10 bait station per 30 to 40 acres of crop field should be sufficient if traps are properly located. In order to gain accurate estimates of the wireworm population, traps should be located in high risk areas such as in any grassy areas of the field or in areas where wireworms caused injury in previous seasons. Although trap placement in fields may occur 2-3 weeks prior to planting of the corn crop, traps placed 7-10 days prior to planting provide more accurate estimates of wireworm numbers as wireworms often remain deep in the soil until soil temperatures warm in the spring. With wet conditions and planting dates rapidly approaching in 2008, 7-10 days of monitoring should be sufficient to estimate wireworm populations in field crops.

This Wireworm trapping technique consists of digging a 4-inch deep by 6-9 inch wide hole at the soil surface. Place into the hole 1 cup of equal mixture of untreated corn and wheat seed which has be pre-soaked for 24 hours prior to use in order to speed up seed germination.. Fill and slightly mound each station with soil. Cover each mound with an 18-inch square of black polyethylene plastic (appropriate sized trash bag) followed by a 1-yard square sheet of clear polyethylene or similar clear plastic bag. Cover the edges of the plastic layers with soil to prevent wind damage. The black plastic layer absorbs heat and the clear plastic helps retain heat in the soil producing a "greenhouse effect" which allows for more rapid germination of the bait seed. Carbon dioxide is produced during the germination process and attracts wireworms to the bait. Just prior to planting, remove the plastic layers and soil from the bait and count the number of wireworm larvae in and around the germinating ball of bait seed. If the average number of wireworm larvae collected in all baits located in the field average one or more per bait station, the economic threshold has been exceeded and treatment is justified. If an economic infestation is found, control options implemented before or at the time of planting are recommended. Management options include such strategies as use of liquid or granular insecticides at planting or planting insecticide treated seed. Rescue treatments for this soil inhabiting insect pest are not available at this time.