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Searching for a Silver Bullet

The clock is ticking on Thimet 15G, the insecticide of choice for controlling wireworm in potatoes in most areas of Canada. Because Canada’s regulators have decided to phase out Thimet due to environmental concerns, the pesticide will no longer be available for use on potatoes as of Aug. 1, 2015.

With wireworm populations steadily rising in Prince Edward Island and other parts of the country, there’s a question hanging over the potato industry that’s being asked more and more often: What will take Thimet’s place?

Fipronil has been viewed by many in the industry as a potential silver bullet for wireworm control. The insecticide is registered in the United States for use on potatoes, and it’s said to be effective against all species of wireworm (and there are many).

However, fipronil is not registered in Canada. It’s up to the chemical industry to decide whether to pursue registration of the product for use on potatoes in this country. That hasn’t happened yet, and there is growing doubt within the potato sector that it ever will.

The irony is that potatoes grown using fipronil are being consumed by Canadians. The United States can export fipronil-treated potatoes into Canada because they don’t exceed the general maximum residue limit (MRL) of 0.1 ppm as specified in Health Canada’s list of MRLs regulated under the Pest Control Products Act.

A further irony is that Canadian potatoes grown with a wireworm treatment like chlorpyrifos can’t be shipped to the United States. That’s because chlorpyrifos is not registered for use on potatoes either grown in the U.S. or imported into that country, and a MRL situation such as that pertaining to fipronil-treated potatoes isn’t possible under American regulations.

All this has some growers in Canada feeling the deck could be stacked against them in their fight against wireworm in the coming years.

That’s not to say there isn’t hope. There are numerous research initiatives involving crop rotations and insecticide efficacy studies underway designed to come up with new ways to combat this destructive potato pest.

In addition, the industry is welcoming the registration just this year of a new insecticide called bifenthrin (Capture) for control of wireworm on potatoes. Growers in different parts of the country are trialing bifenthrin on potato plots this summer to see for themselves how the chemistry stacks up against Thimet and other available wireworm control measures.

For the sake of Canada’s potato industry, here’s hoping everyone is pleased with the results.

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