Wireworms
Pacific Coast Wireworm
Sugar Beet Wireworm
Western Field Wireworm
Columbia Basin Wireworm
Great Basin Wireworm
Description
Adult: Adults are known as click beetles. They are about 6 to 13 mm long, with a hard-shell body that is black to brown. They make a distinctive clicking noises with a “hinge” between the thorax and abdomen and use this clicking mechanism to fling their body to escape threats.
Egg: Small, round, and white, eggs are laid singly or in clusters in the moist soil of grassy areas.
Larva: About 13-38 mm long when mature with a wiry look, larvae are shiny white at first, but become light brown or straw-colored with age.
Pupa: White-colored, a pupa is contained in an earthen cell in the soil.
General Life History
Adults overwinter in the soil and emerge in late April to early May in northern Utah. Between late May and early June, females lay 50 to 400 eggs in the soil about 6 inches deep. Larvae live in the soil for 1 to 6 years and are closer to the soil surface in spring and fall. During hot summer periods, larvae move deeper into the soil. Some larvae can be found at depths of 1-5 feet.
Damage
Limonius species (Pacific Coast, sugar beet, western field, Columbia Basin wireworms) favor moist conditions while Ctenicera pruinina (Great Basin wireworm) prefers dry lands where annual rainfall is less than 15 inches. All crops are susceptible to wireworm attack; however, bean, grain, corn, potato, and other annual crops are preferred hosts.
Wireworms may feed on planted seeds, causing failure to germinate. They can also feed on plant roots, causing the death of young plants. Bare spots in the fields and dead or wilted young plants may indicate wireworm infestation.
In Utah, the Great Basin wireworm has reportedly chewed holes through drip tape.
Monitoring
Inspect the soil surface for wireworms after plowing or disc ing fields. Baits such as carrots, untreated corn or wheat seed, or ground whole wheat flour can also be used to detect wireworms. Place baits 4-6 inches deep in the soil when soil temperatures are at 50 °F. If wireworms are detected, collect soil samples in spring with a 6-inch post hole digger and a shake/sifter to estimate the density of wireworms. Table 6.3 shows a soil sampling guide from the University of California.
Wireworm Soil Sampling Guide
| Acres in Field | Number of Soil Samples | Treatment Threshold (#of wireworms) |
|---|---|---|
| 10 | 30 | 1 |
| 22 | 45 | 2 |
| 40 | 60 | 2 |
| 90 | 90 | 4 |
| 160 | 120 | 5 |
Management
Wireworms are common in Utah, but do not often cause damage. Once present in a field, wireworms can be difficult to eradicate.
Cultural
- Establish a dense plant stand. Reduce the impact of wireworm damage.
- Rotate crops. Fields previously planted to grasses, including grass grains or pasture, are at a higher risk for high wireworm populations. Red and sweet clover and small grains, especially barley and wheat, can increase wireworm populations. Include alfalfa and mustards in crop rotations to reduce wireworm populations over time.
- Practice sanitation. Remove dead plants throughout the season and at harvest.
- Dry the soil. Sugar beet and Pacific Coast wireworm (Limonius spp.) populations prefer moist soil and can be reduced by drying the top 15 inches of the soil for several weeks at midsummer. This will especially kill eggs and young larvae. Soil drying is more effective in light sandy to silt loam soils. Conversely, Great Basin wireworms (Ctenicera spp.) prefer dry soil and can be eradicated by converting dryland fields to continual irrigation.
- Flood the soil. Thoroughly saturate or flood soils for at least 2 weeks when soil temperatures are above 68 °F to significantly reduce wireworm populations. To increase wireworm mortality, alternate periods of flooding and drying.
- Use intensive plowing. Reduce wireworm populations plowing three or more times during late spring and early summer.
- Maintain soil health. Maintaining healthy soils with compost, manure, or green manures, may reduce wireworm damage.
- Place drip tape atop of the soil rather than covering it with soil. This avoids holes created by chewing larvae.
Chemical
Chemical options for wireworm control are few. Organophosphate chemicals are most effective and consistent when applied at preplant as a broadcast treatment, or at planting time as a furrow application.
Biological
Birds may feed on wireworms in recently plowed fields but will not reduce populations below economic levels in seriously infested areas. There are no known biological insecticides.