Wireworms can be destructive to corn, potatoes, wheat, barley and onions in Manitoba. The larvae feed on germinating seeds or young seedlings, shredding the stems but seldom cutting them off. The central leaves die but outer plant leaves often remain green for some time. Damaged plants soon wilt and die, resulting in thin stands. Because thinning can also be caused by poor seed and dry conditions, many wireworm infestations are passed off as being poor seed or poor germination.
Wireworms do 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 where it is cooler and where moisture is plentiful. They may feed on the small roots of host plants, stunting and sometimes killing the plants. Tubers of potatoes may be burrowed into, rendering them unmarketable. The fact that wireworms prefer well-drained sandy soils may have something to do with their prevalence in these areas. Mortality caused by bacterial diseases is especially high in soils of high moisture content.