Wireworms are among the handful of soil-dwelling insect pests that concern corn producers each growing season. Although wireworms damage less than 1% of the corn crop in Illinois every year, growers with wireworm problems do not consider wireworms to be a secondary pest. However, concern about potential wireworm damage does not justify the widespread use of soil insecticides on first-year corn planted after soybeans. Therefore it is really important for growers to have some way to anticipate wireworm problems. Unfortunately, infestations of wireworms are difficult to predict. The occurrence of wireworms usually is related to the crops or weeds that were growing in the field 2 to 4 years before damage to the corn in the current growing season becomes obvious. Fields with the greatest potential for wireworm damage include corn planted after small grains (including corn planted after double-cropped soybeans) and grass sod. |
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 may support wireworms because of the weed populations that tend to occur in those areas. In other instances, wireworms seem to be concentrated in high areas of the field. Crop residue also attracts female click beetles that are laying eggs. Unfortunately, when all is said and done, the relationship between wireworms and field conditions is not well understood.
Wireworm larvae in bases of corn stems.
Wireworms attack the seeds and the portion of the corn stem below ground, often damaging or killing the growing point. Infested fields usually have spotty stands with significant reductions in plant population in some areas. Because no effective rescue treatments for wireworms exist after the infestation has been discovered, you must detect their presence before planting if you want to take any preventive action. We recommend a baiting technique that aids in the detection of wireworms before planting.
Follow this procedure for establishing bait stations 2 to 3 weeks before the anticipated planting date:
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 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 2.
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 are usually hard, smooth, dark reddish brown, and wirelike. However, some species are soft-bodied and are white or yellowish.
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 (Agrox DL+, Kernel Guard, ProShield with Force ST) or a soil insecticide (Table 3). A seed treatment will protect the seeds but will not prevent wireworms from attacking the stem beneath the soil surface. If your baiting procedure pinpoints 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.--Mike Gray and Kevin Steffey