Wireworms are among the so-called secondary insect pests that have caused considerable damage to cornfields in recent years. Along with grape colaspis, white grubs, and a few other notables, wireworms have become a focus of attention for a lot of agriculturists in Illinois. Everyone should realize wireworm infestations cannot be controlled with "rescue" treatments after the fact (i.e., after the damage is discovered). Consequently, knowledge of the presence (or absence) of wireworms before planting corn is the best way to make plans for their control. Although anticipating the occurrence of most secondary insect pests is challenging (to say the least), wireworms can be detected before planting.|
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 corn occurs, primarily because the larvae live for 2 to 6 years in the soil. Fields with the greatest potential for wireworm problems include corn planted after small grains (including corn planted after double-cropped soybeans) and grass pastures or grass hay. Many species of click beetles (the adult stage of wireworms) prefer to lay their eggs in grasses. Depending on the species (there are many that occur in Illinois), wireworm populations may be concentrated in low, poorly drained areas of fields or in high, drier areas of fields.
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. 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 always win out.
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 usually are hard, smooth, dark reddish brown, and wirelike. However, some species are soft-bodied and are white or yellowish.
Wireworms found in a cornfield.
6. Place about a dozen bait stations per 40 acres. Your placement of the bait stations should represent different areas of a field.
A video clip that shows the procedure for placing a solar bait station can be accessed at http://ipm.uiuc.edu/publications/videos/video.html. The video also is available on the IPM Online Companion CD.
If you find an average of one or more wireworms per bait station, consider the use of a registered seed treatment or a soil insecticide (refer to Table 1 for options). A hopper-box seed treatment (e.g., Agrox DL Plus, Kernel Guard) 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.--Kevin Steffey