Potato blights develop fungicide resistance

(REVISED) — Leaf samples taken last summer by provincial potato specialists and ag chem firm Bayer CropScience show “widespread” presence of fungi that have mutated to resist the fungicides used most often to control them.

The sampling program found 113 isolates of Alternaria solani, the cause of early blight in potatoes. Of those, Bayer said in a release last week, over 80 per cent carried the F129L mutation that causes “reduced sensitivity to strobilurins.”

That’s not to say strobilurins won’t work at all, but that they “don’t work as well as they have in the past for controlling early blight,” Bayer said.

Early blight leaf tissue samples were collected during the summer of 2008 in Alberta, Manitoba, Ontario and Prince Edward Island by potato specialists and Bayer sales reps, the company said.

“Initial results confirm that mutant strains are widespread in Alberta, Manitoba and Ontario, which is not surprising given the widespread distribution of mutant strains of the early blight fungus in the United States,” said Rick Peters, a research scientist with Agriculture and Agri-Food Canada at Charlottetown, in Bayer’s release.

“To date, P.E.I. is the only area that we’ve surveyed where all samples were still sensitive to strobilurins, likely due to the less frequent use of strobilurins in this province.”

“We’re putting our heads in the sand if we ignore this growing issue with reduced sensitivity to strobilurins,” said potato pest specialist Tracy Shinners-Carnelley of Manitoba Agriculture, Food and Rural Initiatives at Carman, Man., also in Bayer’s release.

“When the risk for early blight is high, look at the tools available and use them appropriately in a planned program. And if strobilurins are part of that program, they must be tank mixed with a protectant fungicide.”

The strobilurins include Group 11 products such as Syngenta’s Quadris and BASF’s Headline, both of which are registered for control of early blight in potatoes. Reason, another Bayer product, is also a Group 11 and for early blight control is tank-mixed with Bravo or Dithane fungicide.

Some products, such as Bayer’s Group 9 fungicide Scala, are also registered for use on early blight in potato crops and allow growers to rotate their disease control products. Scala recently picked up registration for use on the Prairies and is registered as a control for early blight in potatoes when tank-mixed with Bravo.

CORRECTION FROM SOURCE, March 17: An earlier version of this story which stated Bayer CropScience’s Scala fungicide is not registered on the Prairies was incorrect.

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