No. 3/April 10, 1998
Wireworms: Have You Checked Your Bait Stations?
If you haven't already established bait stations in your fields this spring to check for wireworms (Figure 2), time is quickly running out. Although bait stations are not easy to establish, they can be useful tools to aid growers in making decisions regarding the wisdom of using a soil insecticide at planting. Recall that rescue treatments are not an option for this insect pest. Once an existing infestation is discovered and plants are being injured, growers are left with few options. Sometimes the decision involves replanting certainareas of a field, which is not a popular practice.
Figure 2. Cross-section of a wireworm bait station.
Check bait stations for wireworms.
The occurrence of wireworms is often related to crops or weeds that were in the field 2 to 4 years before damage to corn in the current growing season becomes obvious. Wireworms have very long life cycles and can live in the soil as larvae for 2 to 6 years. Adults (click beetles) can live for 10 to 12 months, preferring to lay their eggs in small-grain stubble, sod, or grass-infested fields. Low or poorly drained areas within fields often support wireworms because weed populations tend to arise in those areas. In other instances, wireworms are concentrated in elevated areas of the field. Typical wireworm infestations are spotty and not uniform throughout a field. Wireworms either attack the seed or drill into the base of the corn stem below groun level, damaging or killing the growing point. Infested fields usually have spotty stands, with significant reductions in plant populations in some areas. The following steps can be followed to establish a bait station.
Research suggests that you should place two bait stations per acre. However, more practical advice is to place about a dozen bait stations per 40 acres. Placement of the bait stations should represent all different areas of a field--the low spots, the high spots, previous weedy areas, or different cropping patterns within a field.
- Dig each bait station about 4 to 6 inches deep and about 9 to 10 inches wide at the soil surface.
- Place 1/2 to 1 cup of an equal mixture of corn and wheat seeds into the bottom of each station. Carbon dioxide produced during germination attracts wireworms.
- Fill and slightly mound each station with soil.
- Cover each mound with an 18-inch square of black plastic; then cover this sheet with a 1-yard square of clear plastic. The plastic increases the soil temperature and speeds the germination of the seeds.
- Cover the edges of the plastic with soil to prevent the wind from blowing the plastic away.
- A few days before planting, remove the plastic and soil covering the bait and count the number of wireworm larvae found at each station. Wireworm larvae are 1/2 to 1-1/2 inches long and are usually hard, smooth, dark reddish brown, and wirelike. However, some species are soft-bodied and are white or yellowish.
If you find an average of one or more wireworms per bait station, consider the use of a soil insecticide at planting. A seed treatment will offer some protection against direct injury to the seed; however, a seed treatment does not prevent wireworms from attacking the below-ground portion of the stem. Products listed in the Illinois Agricultural Pest Management Handbook for wireworms include *Aztec 2.1G, *Counter CR, *Force 1.5G/3G, and *Fortress 2.5G/5G. (* = Use of product restricted to certified applicators only.)
Mike Gray (firstname.lastname@example.org) and Kevin Steffey (email@example.com), Extension Entomology, (217)333-6652