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Wireworms

Melanotus spp., Agriotes mancus Say, and Limonius dubitans LeConte

Appearance and Life History

Adult wireworms are called click beetles. Their name comes from the clicking sound they make while attempting to right themselves after falling or being placed on their backs. Several species of wireworm larvae damage cereal and forage crops while feeding on underground portions of plants.

Wireworms are slender, hard-bodied, wire-like larvae that can damage young corn plants. They are shiny yellow to brown in color and range in size from 1/2 to 1-1/2 inches (13 to 38 mm) long. Since the life cycle of certain wireworm species may last from 4 to 7 years, larvae may damage several successive crops.

Click beetles lay tiny, white, round eggs in the soil, usually near the roots of grasses or grass-like crops in the spring. Damage by first-year wireworms is minor, feeding by the larger larvae in subsequent years is normally when economic damage occurs.

Damage

Wireworm larvae may feed on the germ of corn kernels or completely hollow out the seeds, leaving only the seed coat. This damage results in gaps in the rows. Wireworms may also cut off small roots or tunnel into the underground portions of the root or stem of young corn plants. These plants will appear stunted or wilted with the whorl leaves wilting first.

Wireworm damage occurs mainly during the early stages of plant growth. Damage commonly occurs when corn is planted early and the weather turns cold, slowing seed germination. Wireworm infestations are usually noted in areas of a field that stay moist for long periods of time. As soil temperatures warm, wireworms move deeper in the soil profile, eventually to where they are no longer a threat to the growing corn.

Sampling Method

Corn fields likely to be attacked by wireworms are those in which sod or small grains were grown the previous year(s), were in set-aside, or which have a history of such damage. Two to three weeks before planting, bait stations should be established in suspected wireworm fields (see following page). In 5 randomly selected areas of a field, bury a mixture of untreated corn and wheat seed (a handful of each) 6 inches (15 cm) deep in the soil. Cover the site with a piece of black plastic to help heat up the soil and mark each site with a flag so that the bait stations can be easily found at a later date. After 2 to 3 weeks, or just before planting, dig up the bait and check for the presence and/or damage of wireworms.

Another pre-plant sampling method is to dig up a 2 feet long by 1 foot wide by 6 inches deep (60 x 30 x 15 cm), 1 cubic foot, section of soil in each of 5 areas in a field approximately 10 days before planting. Place the soil on a piece of black plastic or cloth or 1/4 inch (6 mm) hardware cloth and carefully search through the soil, counting the number of live wireworms found.

If suspected wireworm damage (i.e., wilted plants or gaps in the rows) is found during an early season field visit, sample the field immediately. In the area(s) where such damage is found, and in 5 randomly selected areas of the field, dig up a 2 feet long by 1 foot wide by 6 inches deep (60 x 30 x 15 cm), 1 cubic foot, area centered over and along the row. Place the soil on a sheet of black plastic or cloth or 1/4 inch (6 mm) hardware cloth and carefully sort through the sample for live wireworms. Also examine the plants for wireworm feeding damage, most notably small, cleanly bored holes at the base of the plants.

Management Guidelines

Corn Insect Control Recommendations: E-series 219-W (PDF)

Control may be necessary at planting if:

1. using a bait station sampling method - an average of one live wireworm per bait station is found or
2. using the soil screening sampling method - an average of one live wireworm per cubic foot is found.

Several insecticides are labeled for wireworm control and can be used as pre-plant or planting-time applications. Control may be highly variable. It may also help to use a seed treatment, if low populations are noted. No insecticides are available to be applied as rescue treatments. If a field is replanted due to wireworms and the wireworms are still present and actively feeding, use a soil insecticide and/or a seed treatment depending on the wireworm population.

The following chart may help when on is considering replanting a damaged field. For example, corn planted on April 25 but with only 16,000 plants per acre because of wireworm damage, is at 86% optimum yield. Replanting on May 21 and obtaining a population of 25,000 plants per acre should increase your optimum yield to approximately 95%. Although this is a 9% increase in potential yield, one must consider factors such as seed and machinery/labor costs, hybrid maturity, and extended weather forecasts before replant decisions are made.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.