Keep Eyes And Ears Open For Corn Wireworms
The corn wireworm (Melanotus communis) is a major pest of corn, sugarcane, potatoes, and sweet potatoes. It also may attack carrots, cucurbits, beans, peppers, and celery, as well as various grasses and flowers.
Wireworms attack mostly seeds, roots, shoots, and crowns of plants below the soil surface. In corn, damage appears in the form of hollowed out corn kernels, leaving only the seed coat. In later stages, larvae also may cut off small roots or tunnel into underground portions of the root or stems of young corn plants. The damage can be recognized in a field by the presence of gaps in rows or stunted or wilted plants with whorl leaves wilting first.
In potatoes, corn wireworms destroy planted seeds, tunnel into plant stems, and bore into roots and crown tissues. They feed on the seed pieces, causing weak stands. But the major yield losses are due to tunneling into tubers, leading to rotting.
The adults are commonly known as “click beetles.” The larvae are hard-bodied and darker colored than most maggots or grubs. They are glossy and yellow-brown, with a wire-like hard, cylindrical, jointed body ranging from 0.51 to 1.5 inches. First-instar larvae are pale yellow and change to reddish brown in later stages. First-year larvae do not cause significant damage.
Survival And Spread
Overwintering adult beetles are nocturnal and emerge from soil in late March or early April. They are most numerous in Florida during April to August, with peak oviposition in May.
Mated females prefer weedy or grassy fields for egg laying. The eggs are tiny and are usually laid in batches of 50 to 130. The larvae develop throughout the summer and overwinter as second-instar larvae in the soil. Most continue to develop over the next five years and undergo molting once or twice each year, but some larvae develop fully in three years. The larvae pupate in the soil for two weeks before emerging as adults. This is the only stage of wireworms that is found above ground.
Scouting of wireworms is very important for its management and it can be achieved by using bait traps. Fields with high wireworm densities in the past tend to retain populations over the years. Low-lying areas and high organic matter also promote wireworm populations.
Few predators and parasitoids are reported for biological control of wireworms. Pre-plant disking and summer plowing of fallow fields might reduce populations but does not prevent Melanotus communis from reaching economically damaging levels. Planting rice or fallow field flooding may eliminate the need to use a soil insecticide the following season.
No insecticides are available for wireworm control once the crop is planted. Preplant broadcasting and furrow application of soil insecticides are commonly used as a preventative measure. Newer insecticides provide effective wireworm control with less environmental impact and fewer potential human safety concerns compared to organophosphates. Consult UF/IFAS recommendations for currently labeled insecticides for wireworm control in Florida vegetables.