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Idaho spud experts advise late blight precautions

By John O’Connell

Capital Press

Experts advise Idaho potato growers to take precautions for late blight due to extremely wet weather.

BLACKFOOT, Idaho — Crop disease experts warn Idaho potato growers that extremely wet weather has created ideal conditions for the spread of late blight disease, and it’s critical that they keep current on spraying fungicides.

University of Idaho Extension potato pathologist Phil Nolte said samples taken Aug. 11-12 from three separate fields in Bingham County have tested positive for the fungal disease, which thrives in prolonged high humidity and warm temperatures. Late blight — the culprit behind the Irish potato famine of 1845 — creates lesions in foliage, surrounded by light-green halos, and can rot tubers.

“I expect what we’ve gotten so far is just the beginning,” Nolte said. “The opportunity for this thing to be explosive in its spread is definitely there.”

It takes four to five days for late blight to incubate, and Nolte said laboratories often place samples in moist baggies overnight to propagate spores and facilitate detection. The disease was far more advanced in this season’s samples, he said.

Shortly after late blight was confirmed, another thunderstorm moved through the area, likely distributing the spores for several miles. Nolte is hopeful a turn toward drier weather in the extended weather forecast will help curb the spread.

Syntenta agronomic service representative Glenn Letendre said the disease can be controlled effectively through preventative spraying, but once infections occur it can “take a field down pretty darned quick.” He said growers applying broad-spectrum herbicides, such as Bravo or Dithane, roughly every 10 days as part of routine programs early blight or white mold should be in good shape.

“If growers have stretched applications to save some money, I would recommend they get in the field and put an application on there,” Letendre said. “It’s a whole lot easier to keep this disease out of a field than to eradicate it once it’s in a field.”

Jeff Miller, president of Miller Research in Rupert, said products that have shown especially good control against late blight include: Omega, Gavel, Tanos, Reason, Ranman, Forum Previcur and Curzate.

“I’ve heard rumors of other samples maybe being found. None of those have been substantiated yet, but with the weather we’ve had it wouldn’t be a surprise,” Miller said.

Miller said at least one case of late blight has been reported in Idaho during each of the past four years, and it was most recently widespread in the state in 2004. He encourages growers to report any late blight detections as a courtesy to neighbors.

In Declo, Mark Darrington has consistently sprayed for early blight but plans to change his chemistry for upcoming treatments to better target late blight. Darrington said he worries about late blight and scouts his fields for it every year.

“We’ll spend the money and switch products and get to something that can control late blight,” Darrington said.

Aberdeen grower Ritchey Toevs believes the chemistry he’s been regularly using for early blight — still his chief concern — should effectively protect him against late blight, too.


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