No. 1 Article 6/March 18, 2004

Searching for Wireworms: The Use of Solar Bait Stations

Several species of wireworms may attack cornfields. Though considered secondary insects, wireworms may cause considerable economic damage to corn. These soil-inhabiting insects cause early-season injury by boring into and hollowing out seeds, preventing germination. They may also bore into the base of seedlings just below the soil line, injuring or killing young plants. Wireworms may be clustered in scattered areas throughout the field. Spotty corn stands may be evidence of wireworm infestations due to lack of germination or wilted and dying seedling plants.

Wireworms found in a cornfield.

Wireworm boring into base of corn seedling.

Wireworm infestations are generally related to crops or weeds that grew in the damaged field 2 to 4 years before. Cornfields planted after small grains (including corn planted after double-cropped soybeans) and grass pastures or grass hay often exhibit the greatest potential for wireworm problems. Wireworms may also be concentrated in low, poorly drained areas of fields or high, drier areas of the field, depending on the species.

Postemergence insecticides or "rescue treatments" are not effective for wireworm control. Ultimately, the only way to know for certain whether wireworms pose a threat is to look for them before planting corn. Efforts to aid the search for wireworms led entomologists at the University of Missouri to develop the idea of solar bait stations (Figure 1). These bait stations are simple to create, and the results are easy to interpret. Although several studies over the years have focused on finding a better way to detect wireworms, solar bait stations have continued to win out.

Follow this procedure for establishing bait stations 2 to 3 weeks before the anticipated planting date:

Figure 1. Cross-section of a solar bait station for sampling for wireworms.

  1. Dig a hole about 3 to 4 inches deep and 9 to 10 inches wide at the soil surface.
  2. Bury 1/2 cup of a mixture of equal parts untreated corn and wheat at the bottom of the hole. The germinating seeds attract wireworms.
  3. Fill the hole and mound a "soil dome" over the covered bait to serve as a solar collector and to prevent standing water.
  4. Cover each mound with an 18-inch-square sheet of black plastic, topped with a 1-yard-square sheet of clear plastic, and cover the edges with soil to hold the plastic sheets down. The plastic collects solar radiation and speeds germination of the corn and wheat. A cross-section of a wireworm bait station is illustrated in Figure 1.
  5. 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 usually are hard, smooth, dark reddish brown, and wirelike. However, some species are soft-bodied and are white or yellowish.
  6. Place about a dozen bait stations per 40 acres. Your placement of the bait stations should represent different areas of a field.

If you find an average of one or more wireworms per bait station, consider the use of a registered seed treatment or soil insecticide (see Table 3 in the 2004 Illinois Agricultural Pest Management Handbook). A hopper-box seed treatment (e.g., Agrox Premiere, Kernel Guard) will protect the seeds but will not prevent wireworms from attacking the stem beneath the soil sur-face. If your baiting procedure pin-points wireworms in a specific area of the field, consider treating only the infested area rather than the entire field. You'll save money by reducing the amount of insecticide applied in the field.--Kelly Cook, Mike Gray, and Kevin Steffey

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