Food & Health
Pulse Crops: Pea, lentil, chickpea
Wireworm larvae are hard, smooth, slender, wire-like worms varying from 1 to 2 inches in length when mature. They are a yellowish-white to a coppery color with three pairs of small, thin legs behind the head. The last body segment is forked or notched. Adult wireworms are bullet-shaped, hard-shelled beetles that are brown to black in color and about an inch long. The common name "click beetle" is derived from the clicking sound that the insect makes when attempting to right itself after landing on its back.
Wireworms usually take three to four years to develop from the egg to an adult beetle. Most of this time is spent as a larva in the soil. Generations overlap, so larvae of all ages may be in the soil at the same time. Wireworm larvae and adults overwinter at least 9 to 24 inches deep in the soil. When soil temperatures reach 50 to 55 degrees Fahrenheit during the spring, larvae and adults move nearer the soil surface. Adult females emerge from the soil, attract males to mate, then burrow back into the soil to lay eggs. Females can re-emerge and move to other sites where they burrow in and lay more eggs. This behavior results in spotty infestations throughout a field. Some wireworms prefer loose, light and well drained soils; others prefer low spots in fields where higher moisture and heavier clay soils are present.
Larvae move up and down in the soil profile in response to temperature and moisture. After soil temperatures warm to 50 F, larvae feed within 6 inches of the soil surface. When soil temperatures become too hot (>80 F) or dry, larvae will move deeper into the soil to seek more favorable conditions. Wireworms inflict most of their damage in the early spring when they are near the soil surface. During the summer months the larvae move deeper into the soil. Later as soils cool, larvae may resume feeding nearer the surface, but the amount of injury varies with the crop.
Wireworms pupate and the adult stage is spent within cells in the soil during the summer or fall of their final year. The adults remain in the soil until the following spring.
Wireworm infestations are more likely to develop when pulse crops follow grasses, including grain crops or pastures. Wireworms damage crops by feeding on the germinating seed or the young seedling. Damaged plants soon wilt and die, resulting in thin stands. In a heavy infestation, bare spots may appear in the field and reseeding is necessary.
There is no easy way to estimate wireworm infestations. Two methods are currently used.
Sample 20, well-spaced, 1 square foot sites to a depth of 4 to 6 inches for every 40 acres being planted. If an average of 1 wireworm per square foot is found, treatment would be justified.
In September, establish bait stations for 2 to 3 weeks before freeze. Place bait stations randomly through the field, but representing all areas of the field. There should be 10 - 12 stations per 40 acre field. Place one cup wheat and one cups shelled corn in a 4- to 6-inch deep hole. Cover grain with soil and then an 18-inch square piece of clear plastic. Dig up the grain. If an average of one or more wireworm larvae is found per station, treatment would be justified.
Several insecticides are approved for use as seed treatments to protect seeds from wireworms and other soil insect pests. Insecticides applied to the seed just before planting time is an inexpensive means of reducing wireworm damage to growing crops. For maximum benefits, treat shortly before seeding; prolonged storage after treatment may reduce germination. If on-farm treaters are used, be sure they are properly calibrated to apply the recommended dosages. Soil applied insecticides also are used to prevent damage to plants from soil insect pests. They are applied as a preventive measure since rescue treatments are generally ineffective. Use of these products should be based on some knowledge of the pest being present which is determined by field scouting. Using soil insecticides strictly as insurance against injury is discouraged.
Click beetles (adult wireworm)
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