Wireworm populations and their damage to crops are increasing and you can help to find a solution for your distinct farming area. Wireworms are the larval stage of click beetles. Lindane (e.g., Vitavax Dual, etc), an organochlorine insecticide, kept wireworm levels low for several decades but this insecticide has been banned since 2004. As wireworm damage in field crops rebounds, entomologist Bob Vernon, is heading a research team investigating new approaches to keep wireworm problems in check.
“A silver bullet approach has disappeared. Wireworm is not like other insect pests where dealing with only one species makes control measures relatively easy,” says Neil Whatley, crop specialist with Alberta Agriculture and Rural Development. “There are some 30 different wireworm species that exhibit variable life cycles and behaviours.”
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Wireworm species vary from region to region and a single field may contain more than one species and, therefore, more than one type of wireworm behaviour. Instead of persisting for only one season like some insect pests, a single larva can feed on plant roots and germinating seeds in the soil for three to five years, depending on the species, before developing into the adult click beetle stage. While some seed treatments (e.g., Cruiser Maxx and Raxil WW) can repel wireworms, these products do not cause them to die and their populations can continue to increase. The effectiveness of these seed treatments also varies with different species.
“Wireworm damage shows up early as crop thinning during stand establishment and most loss occurs during the earlier part of the growing season before larvae burrow deeper in the soil to escape warm summer temperatures,” says Whatley. “Wireworms feed on the seeds, roots and stems of developing seedlings, often burrowing into the stem of larger plants at ground level. Unlike cutworms, wireworm larvae appear to shred or produce holes in seedling stems, at or below the soil surface, rather than cutting them off. While central leaves die, outer leaves often remain green for some time before eventually wilting and dying, resulting in thin or patchy crop stands.”
Crops grown in recently broken sod are especially vulnerable for one or two years, then damage decreases rapidly only to gradually increase in succeeding years if no wireworm control measures are applied and cereal crops are in the rotation. Wireworms prefer eating annual and perennial grasses, so due to extensive egg-laying in these habitats, populations can build up in fields that have extended periods of pasture or cereal crops. This means that wireworm risk remains high when canola, potato, sugar beet, etc. are subsequently incorporated into the field rotation after cereals and pasture.
“When wireworms complete their life cycles and adult click beetles are formed in a year when a cereal crop is planted, the conditions are optimal for a huge, single-year increase in wireworm populations in that field,” says Whatley. “This increased threat will persist for the next three to five years until the adult click beetle generation is eventually formed again. This scenario may account for situations where wireworm populations are reaching epidemic proportions in some areas and in some fields.”
Send samples
By sending wireworm samples to Vernon and his technician Wim van Herk, you contribute to finding a solution for your region. The research team needs to know which specific wireworm species dominate in your area so the correct control option(s) are selected.
To obtain live wireworms, you may need to bait them by burying whole potatoes or bait balls (gauze packets containing about one cup of wheat seeds, bran, or other cereal-based product) about four to six inches deep at marked locations randomly across a field (or, if the crop is up, in thin, patchy areas) in either early spring or early to mid-August when the worms are nearer to the soil surface.
Dig these baits up 10 to 14 days later (no longer or the baits become repulsive), searching for wireworms and their tunnels. Collect wireworms, along with some of the field soil that is not too wet, and put them in a hard plastic container for shipping. There may be more than one species present, so collect as many as possible. Mail these wireworm samples to: Bob Vernon Agriculture and Agri-Food Canada 6947 #7 Hwy P.O. Box 1000 Agassiz, B.C. V0M 1AO Please include a brief description of where the sample was collected (nearest town or address), what crop the wireworms were found in, any information about previous rotations in that field over the past four years, your name and phone number. Once identified, you will be contacted with the results.
