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Regulatory changes by the Pest Management Regulatory Agency (PMRA) are limiting fungicide options for Ontario potato farmers.

That means more cost and more chance of resistance, says Darin Gibson with Gaia Consulting Ltd. in Manitoba. He spoke on the topic at the 2020 Ontario Potato Conference held in Guelph March 5.

Why it matters: The number of products with more limitations will mean significant new labels to learn and restrictions to manage.

Group M fungicides are under evaluation by the PMRA regarding regulatory issues and concerns for human and environmental health.

Group M fungicides have a multi-site mode of action making it easy for potato producers to use them all season long with low resistance potential.

“This year the biggest change is chlorothalonil. We are down to three applications now,” says Gibson.

Metiram, which is found in Polyram, has been discontinued.

Producers are waiting for the final decision on Mancozeb expected this June. Gibson says they may settle on having three applications but no one is sure.

Captan, although not traditionally used on potatoes, is a reliable option with a maximum of three applications.

“(Farmers) are going to have to depend on different modes of action, mostly single site products with a higher risk of developing resistance.”

Gibson says that although products may be tank mixed, late and early blight programs should be considered as two separate things.

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When reviewing early blight products, such as Quash, Aprovia Top, Quadris Top, Sercadis, Luna Tranquility and Scala, most of them are limited to only three applications and mainly consist of Group 3 and Group 7 fungicides.

“Lots of products (are available), but you have to watch the groups.”

There are numerous other factors for farmers to consider with the loss and potential loss of important fungicides because many are required to be tank-mixed with other products.

For example, Forum fungicide must be tank-mixed with either Polyram DF, Dithan DG Rainshield or Bravo 500.

“Polyram has been discontinued, dithane is a proposed cancellation and Bravo has been limited to three applications. We don’t even use Bravo 500 anymore; we use Bravo Zn.”

Group M pre-mixes will also be affected as Gavel 75 DF and Ridomil Gold MZ contain Mancozeb at 66.7 per cent and 64 per cent respectively.

Looking at a typical Manitoba fungicide program there are 13 applications with Penncozeb, six of these applications being tank-mixed with Quadris Top, Luna Tranquility and Phostrol.

“This happens to the best price point, at least it was last year at $195.”

Gibson suggests a new program for 2019 as regulation will only allow three applications of Penncozeb.

However the suggested 2019 program has already become obsolete as Bravo/Echo is down to three applications, Polyram is gone, if the proposed Mancozeb decision stands and if Captan isn’t available.

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Mancozeb and Polyram will need to be replaced with more expensive products and additional early blight products will be needed. This will create more cost for farmers.

Gibson’s suggested new program has a 85 per cent price increase.

“If you don’t like the $200 program, you’re going to hate the $400 program.”

There are new early blight products coming down the line from BASF and Syngenta, which is promising, but again they are Group 3 and Group 7 fungicides.

“You can be selecting for both late and early blight resistance if you don’t rotate your products.”

It’s important for producers to follow the labels once they are published and use PMRA to find the official label.

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“Use the label (on the bottle) to get the PCP number and then go to the website to get the proper label.”

It’s important growers start to consider late blight and early blight fungicide programs separately with more single site options.

“It’s going to get more expensive and more complicated to protect your crop,” says Gibson.