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Wily wireworm remains a mystery

Lack of effective control allows pest to flourish

Dallas Leduc says he hasn’t noticed any particular yield losses he can blame on wireworm damage in crops on his southern Saskatchewan, grain, oilseed and pulse crop operation, but then for many years they’ve also made a point of using recommended seed treatments as well.

“The pest is out there and we may have the odd spot where we see the effect, but nothing too serious,” says Leduc who farms near Glentworth, about two hours southwest of Moose Jaw. “My dad was always a big fan of using seed treatments. Years ago, he always used Vitavax Dual, and today we continue to use recommended products.”

The old Vitavax Dual was a seed treatment that contained the active ingredient lindane. It was a very effective product that actually killed the crop pest, but after years on the market it was withdrawn due to its residual nature that caused environmental and health concerns. That was in 2004.

This photo of a wireworm-infected field was taken near Pincher Creek, Alta., in May 2017.
photo: Haley Catton

Since then many of the common seed treatments used today were developed around a family of chemicals known as neonicotinoid pesticides (commonly referred to as neonics) with active ingredients such as clothianidin, imidacloprid and thiamethoxam. These neonic seed treatments have protected crops, but really haven’t done anything to control the pest. The neonic chemical stuns, or paralyzes, or puts the feeding wireworm larvae into sleep mode during a critical crop growth stage, but it doesn’t actually kill the pest. That’s led to a fairly robust wireworm population over an ever-expanding area of Western Canada.

“Since lindane was removed from the market we are starting to see wireworm in areas where it hasn’t been before,” says Scott Meers, Alberta agriculture entomologist. “Wireworm was generally considered a pest of southern Alberta or the southern Prairies, but now we are seeing farmers in central Alberta struggling to get crops established due to wireworm. The existing seed treatments put the pest to sleep but don’t control it.”

As prevalent as wireworm has become, there really isn’t a great understanding of the pest, says Haley Catton, a research scientist, cereal crop entomology, with Agriculture and Agri-Food Canada at the Lethbridge Research Centre. She has been studying wireworm for the past 3-1/2 years.

Catton was checking out a theory that including canola in crop rotations might help, reduce wireworm populations. “In Eastern Canada it appears brown mustard in rotation has an effect on wireworms,” says Catton. “We don’t have brown mustard, but we do have canola, but apparently it doesn’t seem to be a factor here.”

Wireworm refers to the larval stage of the adult click beetle, and there are several different species of click beetles, says Catton. The several species found in Western Canada are all native pests and well adapted to their environment, while many of the eastern wireworms were actually introduced from Europe.

Wireworms are a tough pest to get a handle on. There are several different species with a range of life cycles depending on the species. They can stay in the larval stage anywhere from three to seven and even up to 11 years, and depending on the time of year the larvae move up and down through the soil profile. “And not every worm that is in the soil is a wireworm,” says Catton. “So they’re not all harmful.”

The dead patch in this field was created by wireworm. This photo was taken in July 2017.
photo: Haley Catton

While the pest is commonly associated with cereal crops — where the click beetle lays its eggs — the wireworm larvae can inflict damage on a wide range of crops from cereals, to pulse crops and even corn. And depending on the infestation, damage can be limited to a few thin patches up to as much as 50 per cent of the crop lost.

“Plowing or tillage doesn’t seem to have an impact on the pest,” says Catton. “Crop rotation also doesn’t seem to have an effect either. Some people recommend seeding early, while others recommend seeding late — so there just doesn’t seem to be any effective cultural practices to help control the pest.”

Catton says field and cropping history may hold some clues to understanding the pest better. “I’ve seen situations where there are two fields side by side and one has a high wireworm population and the other doesn’t, so understanding field history might provide some answers,” she says.

While research, so far, hasn’t produced any effective control measures, Catton is working to produce a field guide to help farmers better understand the pest.

BASF plans true wireworm control

BASF is expecting its new seed treatment product, Teraxxa, will be a game changer in helping western Canadian farmers control what appears to be an ever-expanding wireworm population.

Teraxxa, expected to be on the market for the 2021 cropping season, is the first seed treatment since lindane, that actually kills the pest, says Chris Hewitt, BASF brand manager, seed treatment.

“It is a new mode of action that rapidly induces wireworm mortal- ity upon contact,” says Hewitt. “It doesn’t just put the pest to sleep, it actually reduces resident popula- tions of the larvae in the soil for true control.”

Farmers and crop entomologists alike, have observed wireworm populations increasing into non-traditional areas of Western Canada over the past 15 years since lindane was removed from the market due to environmental and human health concerns.

Newer seed treatments developed around a family of chemicals known as neonicotinoid pesticides (commonly referred to as neonics) have been effective in protecting the crop, but not in controlling the pest. The larvae would rebound as the chemical wore off. In most cases the crop would have sufficient growth and vigour to with- stand later feeding pressure by the larvae.

While the neonics are Group 4 insecticides, Teraxxa has a Group 30 new mode of action developed around the active ingredient brolanilide. Initially the new product will be registered for wireworm control in cereals such as wheat, barley, oats, rye and triticale.

About the author

Field Editor

Lee Hart is editor of Cattleman’s Corner based in Calgary.

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