Wireworm larvae can damage grain, seedlings, plant roots, and stem bases. Shortly after the plants emerge, brown, discolored leaves appear, and growth typically stops. The larvae feed on the tissue, leaving fibrous feeding spots on the roots and stem bases. If the wireworm larva feeds upwards through the root head, it first affects the heart leaf, followed by the younger leaves, which die. However, the infestation usually occurs from the side, towards the growing point. The outermost leaves may change color irregularly and die quickly after the leaf veins are severed. The plants usually die, possibly producing heavy tillering, and are unable to reach their full yield potential. Areas with increased wireworm infestation are typically easy to recognize.
Symptoms can be confused with frit fly damage or emergence diseases.
The damaging wireworm larvae have a highly resistant chitinous layer, are 2-4 cm long, round, and yellow-brown. The adult click beetle is brown to black and about 10 mm long. It prefers moist, densely vegetated, and humus-rich soil, where it lays up to 230 eggs in early summer. The first larval stage hatches in 4-6 weeks. The entire larval development takes 3-5 years, with damage increasing over time, as larvae cause more harm from the second year onward. Wireworms are particularly common on former grassland, where they can only cause damage 2-3 years after plowing.
The damage threshold for maize is 1-2 wireworms per square meter. The type of wireworm affects the extent of the damage, but determining the wireworm load in a field is difficult. The distribution and activity of the larvae depend on many factors.
Containment measures include: