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Mature larvae of the Hypnoidus bicolor (top) and Selatosomus destructor, the two most important wireworm pests in the Prairie provinces.

Controlling Wireworms

As the situation worsens in potato fields in Prince Edward Island and other areas of Canada, the search is intensifying for a chemical replacement for Thimet. Is bifenthrin, the active ingredient in recently registered pesticide Capture, the answer?

With wireworms on the rise in Canada — and the main weapon against them soon to be taken off the market — it’s a question that’s top of mind for many potato producers these days.

Is there another silver bullet out there that will take the place of Thimet?

Wireworms are thin, hard-bodied larvae of the click beetle that feed on the roots of cereals and other crops including potatoes. In recent years, Thimet 15G has been the insecticide of choice for potato growers fighting to control this voracious pest in the hardest-hit areas of the country, such as Prince Edward Island where producers have been plagued by wireworms for years and the problem continues to worsen.

However, Canada’s regulators are phasing out Thimet as a result of environmental concerns, and the organophospate insecticide will no longer be available for use on potatoes as of Aug. 1, 2015.

This move is part of the National Pesticide Risk Reduction Strategy for Wireworm, devised by Agriculture  and Agri-Food Canada along with Health Canada’s Pest Management Regulatory Agency.

The AAFC’s webpage outlining the strategy states: “Traditionally, wireworms have been controlled using organophosphate insecticides. There is significant risk associated with the use of organophosphate products and they are therefore being withdrawn from registration. The strategy developed for wireworm risk reduction is thus centered on the need to find lower risk replacement pest control products and practices for the control of wireworm in Canadian agriculture.”

Under the strategy, researchers have been investigating new options for wireworm control, which include numerous initiatives involving different combinations of crop rotations as well as insecticide efficacy studies.

Many in the industry have held out hope that fipronil, a successful weapon against wireworms in potatoes in the United States, could be the silver bullet to replace Thimet and provide effective, long-lasting control of the pest in Canada.

Fipronil, however, isn’t registered in this country, and it’s up to the chemical industry to decide to pursue registration of the product for use on potatoes in Canada. That hasn’t happened yet and isn’t likely to anytime soon, according to Bob Vernon, who leads an AAFC national wireworm research project.

Tuber containing mature larvae of the Pacific Coast wireworm, Limonius canus.

Tuber containing mature larvae of the Pacific Coast wireworm, Limonius canus.

Vernon says a top priority for his team is finding a replacement for Thimet. One of their strategies involved combining very low amounts of fipronil with low amounts of an neonicotinoid insecticide, creating an effective treatment for wireworms in cereal crops.

“It (fipronil) was a perfect fit for wireworm control in Canada,” says Vernon, adding that the low dosage of fipronil used in his wireworm treatment — less than one gram of fipronil per acre — would result in a much lower environment impact than Thimet, for example.

New Product on Market

There may be hope on the horizon, however. The industry is welcoming a new weapon against wireworm this year with the introduction of Capture. Registered by FMC for controlling wireworm in potatoes and raspberries this past May, the new insecticide features a synthetic pyrethoid known as bifenthrin as its active ingredient.

“Bifenthrin does not degrade in light or soil like regular pyrethoids and will give the growing season control of wireworm damage,” says McMillan, FMC’s business manager for Eastern Canada.

McMillan says the company’s bifenthrin product is known as Brigade in the United States, and that it’s has been used extensively for many years to control wireworm damage in potatoes south of the border. However, he sounds a cautionary note for Canadian growers hoping for a silver bullet.

“It’s not the silver bullet that’s going to eliminate the wireworm issue,” he says. “Wireworms are still going to be an issue. But Capture certainly provides a protective zone like Thimet to help protect the tubers against wireworm attack.”

McMillan maintains Capture studies conducted in Canada over the past few years have concluded the product compares favorably to Thimet in controlling wireworm damage.

He says growers in Prince Edward Island have used Capture on potato fields this summer for the first time and they will be able to evaluate for themselves how the pesticide stacks up against Thimet. McMillan says his preliminary observations during a recent visit to Prince Edward Island looked very promising, indicating that Capture would likely give the same tuber protection from wireworm that Thimet does.

Tracy Shinners-Carnelley, research and quality enhancement director for Manitoba’s Peak of the Market, says with the clock is ticking down on Thimet, growers are eager for any good news related to alternative wireworm treatments.

“There is certainly interest to try bifenthrin on a field scale at the farm level to get a good sense of how it really does compare to Thimet,” she says.

Vernon and his team have assessed the efficacy of the new insecticide in plot trials and he says in trial work, bifenthrin works quite well. Because the product in not systemic, he adds, the best results were produced when Capture was used in combination with a neonicotinoid insecticide like Titan or Admire to provide above-ground protection against pests like Colorado potato beetle.

Wireworm populations right across Canada are growing and in some areas they are reaching epidemic levels. And if we don’t have something that will control them, then we’re in big trouble.

– Bob Vernon

“Bifenthrin, along with a neonicotinoid, appears to give the same level of crop protection in general as Thimet does,” says Vernon. He stresses, however, that additional field studies and continued research are required to adequately assess whether wireworms are actually killed by Capture, or if they are just being repelled or suppressed by the chemical.

Vernon says the fact that some growers have been able to trial Capture on their own farms this year will go a long way towards determining the product’s efficacy on a large scale.

“I’m somewhat optimistic about bifenthrin, but I’m a little worried that we’re going to be taking one product off the market and simply replacing it with another, leaving farmers with just one chemical,” he says. “It would be great to have two products that you can use to combat this pest in terms of resistance and that sort of thing.”

Vernon also stresses the urgency of having a proven alternative to Thimet in place and readily available for potato producers — before Thimet is taken off the market next summer.

“Our farmers have to have something that gives them exceptional control, especially in Prince Edward Island where wireworm pressure is extremely high and getting higher,” he says.
“This is also happening on the Prairies —wireworm populations right across Canada are growing and in some areas they are reaching epidemic levels. And if we don’t have something that will control them, then we’re in big trouble.”

1 Comment

James Bridges - Reply

I am having a great deal of problems with the wire (devils) as I call them. I live on Vancouver Island and would be very interested in any thing you could recommend to me that is legal for use here. Thanking you for being here to help. ( the stick in the potato trick is not of much help on a large property)

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