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Wireworm Control A Looming Problem

Wireworm control could become a troublesome issue for Canadian potato growers in the next couple of years, says a research scientist from AAFC’s Agassiz Research Centre in British Columbia.

But Bob Vernon told the recent Manitoba Potato Days meeting that the best control tool on the market is about to disappear, which could leave Canadian growers at a disadvantage to their American colleagues.

“Thimet will be gone in 2012, and they’ll probably still have it in the U. S.,” Vernon said.

It was set to be pulled from the market in the fall of 2008 by Health Canada’s Pest Management Regulatory Agency (PMRA) due to concerns over the active ingredient, a restricted organophosphate insecticide called phorate.

It received a four-year reprieve because there were no “reasonable alternatives” but Vernon says that deadline is rapidly approaching. There are other products in the approval pipeline, but none seem to be quite as effective as the old chemistry and exactly when they’ll be registered is uncertain.

Thimet will be available for sale in Canada until Dec. 31, 2011 and can be sold by its retailers and distributors until May 1, 2012. Farmers will be able to use the product until Aug. 1, 2012.

But in the spring of 2013, wireworm control will be a whole new ball game.

“These old-school chemicals are good – they all kill wireworms,” Vernon says.

LESS TOXIC, LESS EFFECTIVE

If there’s a common theme among all the major new candidates for a Thimet replacement, it is that they’re less toxic, but also generally less effective.

Vernon says it remains unclear whether the proposed replacements will work as well, how they work and whether they will outright kill the pests or only offer growers a window of protection.

One major chemistry class that’s being examined is the neo-nicotinoid family and Vernon says field trial results look impressive – at least initially.

“When wireworm is exposed to a neo-nicotinoid, they’ll writhe around, fall to the ground, lay there and appear dead,” Vernon says. “Then they’ll recover three to four months later.”

That means growers aren’t going to have the type of multi-year control they’re accustomed to getting with their current control options.

Pyrethroid-based products have shown a similar control-not-kill activity on wireworm as well, but more importantly the treatment seems to repel the pests from treated crops before they receive a toxic dose.

Chlorpyriphos products such as the organophosphate Lorsban, on the other hand, do kill the pests, but not immediately. It takes seven to 14 days to show its full activity, says Vernon.

NOT APPROVED IN THE U. S.

One of the best chloropyriphos options appears to be Pyrinex 480EC, which gives control that appears roughly equal to Thimet. It and Pyfiros 15G are available on a minor-use registration for potato growers. There’s just one hitch for Canadian growers that are dependent on export markets to the U. S., such as Manitoba process growers.

“Chloropyrifos is not registered on potatoes in the U. S., so there’s a zero tolerance for residue,” explains Vernon. “If the potatoes are destined for the U. S. in either raw or processed form, don’t use chloropyrifos.”

There’s also the broad-spectrum insecticide fipronil, which works by disrupting the central nervous system of insects. It works too, but just how effective it is depends on the size of the dose. In a very large dose it kills the insects quite quickly, but in a smaller dose it’s not as clear cut, Vernon says.

“They’ll appear perfectly healthy, then die about four months later,” says Vernon.

In the larger doses it appears to have a lot of promise – but when or if it will be available to Canadian growers is an open question, says Vernon.

“Registration in Canada is going to be a challenge,” he says.

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Gord Gilmour

Gord Gilmour is Editor of the Manitoba Co-operator.

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