Scouting for Wireworms

April 2, 1999
Wireworms are among the handful of soil–dwelling insect pests that concern corn producers each growing season. We still believe that wireworms damage less than 1 percent of the corn crop in Illinois every year. Consequently, concern about potential wireworm damage does not justify the widespread use of soil insecticides on first–year corn planted after soybeans. Unfortunately, infestations of wireworms are quite difficult to predict from one year to the next. The occurrence of wireworms is usually related to the crops or weeds that were growing in the field two to four years before damage to the corn in the current growing season becomes obvious.

Fields with greatest potential for wireworm damage include corn planted after small grains and grass sod. Growers who plant corn after soybeans double–cropped with wheat also may experience wireworm problems.

Wireworms have very long life cycles and can live in the soil as larvae for two to six 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 of the weed populations that tend to occur in those areas. In other instances, wireworms are concentrated in high areas of the field. In fact, typical wireworm infestations are spotty rather than uniform throughout a field. A review of the field history and the previous conditions of infested areas may provide some insight into the potential for wireworm problems.

Wireworms attack either the seed or the base of the corn stem below ground level, damaging or killing the growing point. Infested fields usually have spotty stands with significant reductions in plant population in some areas. Because there are no effective rescue treatments for wireworms 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:


  1. Dig a hole about 4 to 6 inches deep and 9 to 10 inches wide at the soil surface.
  2. Place a mixture of 1 cup of shelled corn and 1 cup of wheat into the bottom of the hole. The germinating seeds will attract wireworms.
  3. Fill and slightly mound each station with soil.
  4. Cover each mound with an 18–inch square of clear plastic. The plastic collects solar radiation and speeds germination of the corn and wheat.
  5. Cover the edges of the plastic with soil to prevent the wind from blowing the plastic away. A cross section of a wireworm bait station is illustrated in Figure 2.
  6. 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 0.5 to 1.5 inches long and are usually hard, smooth, dark reddish–brown, and wirelike. However, some species are soft bodied and are white or yellowish.
  7. Place about a dozen bait stations per 40 acres. Your placement of the bait stations should represent all areas of a field. If you find an average of one or more wireworms per bait station, consider the use of a seed treatment (diazinon + lindane) or a soil insecticide. A seed treatment will protect the seeds but will not prevent wireworms from attacking the stem beneath the soil surface. Suggested soil insecticides are presented in Table 2. 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.--MG, KS


Figure 2. Cross section of a solar bait station for wireworm detection.


Table 2. Insecticides suggested for control of wireworms in corn.


Insecticide

Amount of product

Placement

Aztec 2.1G*

6.7 oz. per 1,000-ft row

Band, furrow

Counter CR*

6 oz. per 1,000-ft row

Band, furrow

Force 3G*

4 to 5 oz. per 1,000-ft row

Furrow

Fortress 5G*

3 oz per 1,000-ft row

Furrow

Lorsban 4E

4 pt

Broadcast, preplant incorporated

Regent 80WG*

0.149 oz. per 1,000-ft row

Furrow

Thimet 20G*

6 oz. per 1,000-ft row

Band

* Use restricted to certified applicators only.

 



Author: Mike Gray Kevin Steffey