Phosphoric Acid Helps In Late Blight Fight

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Manitoba potato producers are looking forward to phosphoric acid being registered for both pre-and post-harvest application for control of late blight.

The product, registered under the trade name Confine in Canada, is a promising post-harvest application that prevents the spread of late blight infections in storage to healthy tubers.

It’s also showing promise as a foliar application with a systemic component, says Rick Peters, a research scientist with Agriculture and Agri-Food Canada in Charlottetown, P.E.I.

Peters said that in-crop application is a couple of years away at least, but that it looks promising.

“Currently it’s only registered for post-harvest application, where it’s very good at treating the infections on the surface of the tubers and preventing their spread, but it doesn’t get inside them and get at it,” Peters said.

That means producers – and processors – will see greatly reduced blight issues and less spoilage in storages. That’s most welcome news to the industry, but it’s the much-anticipated approval for foliar applications that really has growers interested. Phosphoric acid foliar applications offer the first true systemic late blight control component that they’ve had in a long time.

“It’s systemic, it moves through the plant to the tubers and it prevents infection in the fields,” Peters said. “All of the products we’ve had since Ridomil resistance became an issue are either surface applications or only have a little bit of movement within the leaves. This is our first true new systemic.”

Preventive, not treatment

But growers shouldn’t be hoping for a return to the good old days of Ridomil either. That’s because Ridomil offered growers exceptional protection and it could do something that none of the subsequent late blight products have been able to replicate – it could wipe out an infection once it was already established in the field.

“In the old days, prior to the mid-1990s, Ridomil could kill the infections in the plant,” Peters said. “But then the populations of the disease changed and we lost that control.”

And will phosphoric acid replace it and offer the same kind of easy and effective control? In a word, no, though it will be a better and more effective option than the current options.

“It definitely won’t be the sort of control we saw with Ridomil,” says Peters. “It will be part of a program. It’s not going to be a stand alone like Ridomil was.”

The 2010 crop marks the first major test of phosphoric acid as a storage treatment in Manitoba. Trevor Thornton, of Crop Care Consulting in Portage la Prairie, said growers in Eastern Canada have been using it for the past three years, but this is Manitoba’s first post-registration battle with late blight.

He said just how effective the product is remains an open question, as you’d expect with any new entry in the market. But anecdotally he says growers are saying they’re seeing an effect.

“Infected tubers are definitely degrading to the point that lesions are opening up on the surface – but those infections do not seem to be spreading to healthy tubers,” Thornton said. “That is exactly what they were told to expect to see.”

But there aren’t any hard numbers to back these observations up, something Thornton says is an issue with any storage product.

“It’s not a field trial where you can compare yields, for example,” he said. “Here you’re looking at what’s happening, but there isn’t necessarily anything to compare it to.”

Except in one case, where a grower noticed that he was finding late blight partway through harvest and began applying Confine to a partially filled storage. There Thornton says the contrast is clear as day.

“You can clearly see the line in the storage where be began the application – there’s no question at all that it’s working,” said Thornton. “We don’t have enough light power, but I keep saying we need to get a picture of it to document it.

“We think it’s doing what we were told it would do – and for the price of it, we’re sure hoping that it’s working.”

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“Youcanclearlyseethelineinthestoragewherebebegantheapplicationthere’snoquestionatallthatit’sworking.”

TREVOR THORNTON

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