Pest description and crop damage Adults are hard-shelled, slender beetles called click beetles. They range in color from tan to very dark brown and are 0.3 to 0.5 inch long. They appear in the spring and summer months.
Larvae are the damaging stage. They are yellow-brown and up to 0.5 inch long. Larvae have three pairs of legs. The last segment of the body is usually pronged or forked at the end. Larvae feed on the roots and into the crowns of plants, killing them or severely stunting growth.
Wireworm-damaged seedling stands often appear yellow, and plants eventually brown and die. Symptoms are apparent in the fall. Occasionally, summer-seeded grass seed is damaged before emergence, and there will be long lines of empty seed furrows.
Biology and life history Adult beetles appear in late spring through summer. Females lay many hundreds of eggs in both fallow and crop land. Eggs hatch in 3 to 4 weeks. Larvae usually infest nonirrigated grass seed land and can live in soil up to 3 years.
Sampling and thresholds Dig deeply to find wireworm larvae. They migrate readily up and down the soil profile. After 2 or 3 inches of rain have fallen in September and early October, wireworm larvae often can be found feeding within the root systems and lower crowns of grasses.
Effective soil-applied insecticides are not labeled for use on grasses grown. Preplant soil fumigation is used in high-value crops and suitable soils.