Wireworms

Wireworms represent the larval stage of the click beetles of the family Elateridae. There are around 9,300 species worldwide, but it is a small handful of species that cause problems in our fields and gardens. Click beetles are 1-2cm long, quite narrow in shape, and can be brown, grey, or black. Most obviously, when turned on their backs they use a special mechanism to right themselves, which produces an audible “click.”

The larvae themselves are tan to orange in colour, cylindrical, hard-bodied (unlike many garden grubs), and 1-4cm when mature. These larvae may live in the ground for 2 to 3 years – some species spend as long as 6 years in their larval stage before pupating and emerging as adults, which then mate and deposit the next generation of eggs back in the soil. This long lifecycle makes wireworms difficult to control.

Female click beetles typically lay their eggs in June and July, which hatch about a month later. The grubs feed most actively in September/October, and again in March to May.

Wireworms may be abundant in lawns without showing any signs of their presence. Lawn space or fields converted to vegetable gardens are particularly prone to wireworms, as well as vegetable plots that abut lawn space, pasture, or other grassy fields. To test if an area is infested, bury full-grown carrots 8cm (3”) deep at 10 or so sites around the plot and check them after 3 days. If the carrots show signs of damage (small pinholes or tracks) then wireworms are present. Grains, carrots, and potatoes are prime targets for wireworms.

Control

There are no effective insecticides against wireworm. Crop rotation will reduce damage. Keep the garden area free from weeds – particularly grasses. Deep cultivation of the soil will expose the larvae, which can be hand picked or left for birds to eat. Inter-row hoeing will produce the same effect.

Perhaps the most effective control is the use of predatory nematode, Heterorhabditis megidis. Predatory nematodes can be applied any time of the year if the soil is above 12°C, or in the spring once weather is regularly abovew 14°C, and when the soil is thoroughly wet. More information on predatory nematodes and their application is available on this site. It may take three applications (in spring, fall, and the following spring) to develop the necessary population of nematodes with which to control wireworms.

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