Wireworms, the larval stage of the click beetle, represent a persistent and often destructive challenge for gardeners and agricultural producers. These soil-dwelling pests damage seeds, roots, and tubers, leading to stand loss and unmarketable produce. Managing this pest requires a dual approach: combining immediate treatment actions with long-term strategies to prevent future infestations. This article provides actionable steps for eliminating existing populations and modifying the growing environment.
Identifying Click Beetles and Wireworm Damage
The adult click beetle is an elongated, hard-shelled insect, typically dark brown or black, which poses no direct threat to plants. Its name comes from the characteristic “click” sound it makes when it flips itself over after landing on its back. The wireworm, its larval form, is the true culprit, spending most of its life feeding underground.
Wireworms are slender and cylindrical, often resembling a piece of shiny wire, with colors ranging from yellowish to reddish-brown. They are hard-bodied and vary in length from one-quarter inch up to one and a half inches when fully grown. The wireworm life cycle is long; larvae remain in the soil and actively feed for two to six years before maturing into the adult beetle.
The damage caused by wireworms is concentrated beneath the soil surface. They bore into germinating seeds, hollow them out, and sever the roots and lower stems of young plants, often resulting in wilting and death. Root crops such as potatoes, carrots, and sweet potatoes are particularly susceptible, exhibiting tunnels and holes that make the tubers unusable. Infestations are often most severe in fields recently converted from grass pasture, as adult beetles prefer to lay eggs in grassy or weedy areas.
Direct Control and Treatment Options
Addressing an active wireworm infestation requires immediate action focused on reducing the population. One effective non-chemical approach is using baits, which draw the larvae to a specific point for easy removal. Gardeners can bury pieces of potato or carrot a few inches deep near susceptible plants, marking the location. Checking these traps every few days allows for the collection and disposal of the wireworms that have congregated.
A targeted biological method involves introducing beneficial nematodes, specifically species like Steinernema carpocapsae or Heterorhabditis bacteriophora, into the soil. These microscopic roundworms seek out and infect the wireworm larvae, killing them within a few days. Nematodes should be applied as a soil drench when soil temperatures are above 54°F (12°C) to ensure they are active and move effectively through the soil.
For severe infestations, chemical applications may be necessary. Soil insecticides, such as products containing bifenthrin or pyrethrins, are most effective when applied before or at planting time to protect vulnerable seeds and seedlings. Newer active ingredients, like broflanilide, are utilized as seed treatments to provide protection. Applying any insecticide requires strict adherence to local guidelines and label instructions.
Mechanical control also aids in population reduction by exposing the larvae. Tilling the soil during warm, dry periods brings the wireworms to the surface. Once exposed, the larvae are vulnerable to desiccation from the sun and predation by birds. Repeat tillage during the late spring or early summer, when wireworms are closer to the surface, can disrupt the larval and pupal stages.
Long-Term Prevention Through Cultural Practices
Long-term management of wireworms is achieved by making the growing environment less hospitable to the adult click beetles and their larvae. Implementing strategic crop rotation is an effective preventative measure. Since adult beetles prefer to lay eggs in grassy areas, rotating susceptible crops like potatoes and corn with non-host crops disrupts the life cycle.
Planting legumes, such as peas and beans, or certain cover crops like buckwheat and mustard, can reduce wireworm populations. Brown mustard, for example, releases natural compounds into the soil that suppress the pests. Waiting three or four years after tilling a grassy area before planting a highly susceptible root crop minimizes damage risk from the long-lived larvae.
Soil management practices also influence wireworm presence, as the larvae thrive in cool, moist, and heavy soils. Improving soil drainage reduces the damp conditions favored by the pests, making the area less attractive for egg-laying and larval development. In poorly drained areas, flooding the soil for at least two weeks when temperatures are warm can also significantly reduce populations.
Controlling grassy weeds and volunteer grains is a necessary preventative step because these plants attract the egg-laying female beetles. Maintaining a clean garden or field edge reduces the number of initial egg deposits, lowering the wireworm population. Adjusting the planting schedule to avoid peak wireworm activity in the upper soil layers can also protect young plants during their most vulnerable stage.