Wireworms

Wireworm larvae feed on germinating seeds or young seedlings. Stems of young seedlings are shredded, usually causing the central leaves to die. Damaged plants soon wilt and die, resulting in thin stands.

Host Crops

Wireworms prefer grasses but often attack corn, carrots, potatoes, wheat, barley, sugar beets, lettuce, and onions. Strawberries are also attacked.

Biology

Wireworms are slender, jointed, and hard-bodied. They have 3 pairs of legs behind the head, and the last abdominal segment is flattened with a keyhole-shaped notch. Full-grown larvae may reach a length of 1-4 cm (0.4-1.5 in.).

Adult beetles emerge from the soil in the spring. From late May through June, the female beetles lay 200-1400 eggs in loose or cracked soil and under lumps of soil. The young wireworms hatch and begin feeding on roots or germinating seeds.

The larval stage lasts anywhere from 1-5 years, depending on the species involved. When full grown, usually in July, the larvae pupate in the soil. The adults do not emerge until the following spring.

May	June	July	August	September
Overwintering larvae become active, some feed, some pupate	Some larvae continue feeding, new adults emerge, mate, lay eggs in soil	Eggs hatch, new larvae begin feeding, older larvae feed, some pupate	Larvae continue feeding, some pupate	Larvae and pupae begin overwintering

Scouting Techniques

Soil samples can be sieved to find any wireworms present in the field. Samples can be collected using a post-hole auger and a series of soil sifting screens or by marking out areas 50 cm x 50 cm (20 in. x 20 in.) and sieving the soil to a depth of 15 cm (6 in.). Repeat in different areas of the field to determine an average number of larvae per square metre (sq. yd.).

Sometimes, wireworm damage is confused with cutworm damage. Remember that, with wireworms, the plant is wilted and discoloured but remains attached to the root. With cutworms, the plants are usually cut off completely at or near the soil surface.

Economic Thresholds

An action threshold of about 32 wireworms per square metre (sq. yd.) is often recommended. If wireworms are found at this or a higher density, seed treatment is usually warranted in following years.

Control Tips

Some agronomists recommend that growers treat seed for 2 consecutive years after breaking sod to reduce the problem to a non-economical level. This should be done only if the risk of an infestation is high.

If wireworms are found in an emerging crop, there is no 'quick fix'. Often, the damage occurs or is seen too late to reseed the damaged patch. Also, the loss in yield does not justify the cost of re-seeding. The best plan is to consider what action may be necessary for the following year.

For further information, contact your GO representative.