‘We’re just seeing the tip of the iceberg’ when it comes to wireworms

Populations are growing and control methods shrinking, says provincial crop specialist

Wireworm damage to field crops is poised to escalate, says a provincial crop specialist.

“For several decades, Lindane (Vitavax Dual, etc.) insecticide applied to crops on the Canadian Prairies kept wireworm numbers low,” said Neil Whatley, crop specialist at the Alberta Ag-Info Centre.

“Since the ban of this organochlorine pesticide in 2004, wireworm damage in field crops is rebounding. Some entomology research scientists say we’re just seeing the tip of the iceberg.”

The problem varies from region to region as the approximately 30 different pest wireworm species exhibit diverse behaviours and life cycles, making a single control measure improbable. Some regions may have more than one wireworm species.

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Depending on the species, the worm-like larvae can feed on plant roots and germinating seeds for up to three to five years before developing into the adult click beetle stage.

Wireworms prefer to eat annual or perennial grasses, so their populations can build up in fields with long periods of cereal or pasture production. Pulses, oilseeds, potatoes and sugar beets are susceptible to wireworm damage when grown in rotation with cereals. Crops grown in recently broken sod are especially vulnerable while grassy ditches and undisturbed field borders can also harbour wireworms and click beetles.

While current insecticidal seed treatments may repel wireworms for a growing season, populations will increase as these treatment measures begin to fail, said Whatley.

“Even these insecticides may be phased out,” he said. “Clearly, an integrated management method that also applies non-pesticide approaches will be required for optimal wireworm management.”

Agriculture and Agri-Food Canada’s wireworm research team is identifying species and researching new control measures. Haley Catton, cereal crop entomologist of AAFC Lethbridge, is the Prairies representative on this team.

“The team is looking at an integrated management approach that includes improved understanding of the contribution of beneficial insects as well as realizing how wireworm communities are affected by various agronomic techniques, including crop rotations,” said Whatley.

“They need to know which specific wireworm species dominates in your farming region so the correct control options can be applied as the problem worsens. The team is asking producers to submit wireworm species from their fields.”

Baiting and capturing wireworms

“Early spring and prior to seeding is the best time to bait and capture wireworms,” he said. “They migrate upwards, towards the soil surface where there’s more moisture. They will ultimately come in contact with the rooting zones of plants in the early spring when the soil temperature rises above 5 C.”

Baiting can be as simple as burying a cup of a cereal-based product (such as flour, bran or wheat seeds) to a depth of four to six inches into the soil at marked locations. The carbon dioxide emitted by germinating plants in the spring attracts wireworms, so the bait material attracts them by mimicking this process prior to plant germination.

Dig up the baits 10 to 14 days later, and collect wireworms and some field soil that is not too wet. Sort through the sample, and pick out as many wireworms as possible. Place them in a small vial with rubbing alcohol as a preservative. There may be more than one species present, so collect as many wireworms as possible.

Wireworm samples should be mailed to:

Dr. Haley Catton
Agriculture and Agri-Food Canada
Lethbridge Research and Development Centre
5403 1 Avenue South
Lethbridge, Alberta  T1J 4B1

Include a brief description of when and where the sample was collected (nearest town or address), information about the crop rotation in the sampled field over the past four years, name and telephone number. Once the species are identified, producers will be contacted with the results.

Catton and colleagues are also writing a wireworm field guide, expected to be released later this year.

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