Late blight continues to spread in Idaho: UPDATED REPORT

UPDATE: On Friday, August 14, Jeff Miller reported that late blight has been confirmed in four more Idaho counties: Madison, Fremont, Jefferson and Cassia.

As of August 12, 2015, late blight has been confirmed in four counties, Minidoka, Bingham, Power and Bonneville. The US 23 late blight strain has been identified in Minidoka, Bingham and Power, samples from Bonneville County have been submitted for testing.

Phil Wharton, potato pathologist at the University of Idaho’s Aberdeen Research and Extension Center, said that weather conditions have been perfect, cool nights with rainstorms moving through, for late blight to spread through Idaho potato fields.

Late blight was first identified in Idaho on July 10.

He said that the most likely cause for late blight was volunteer potatoes.

There were perfect conditions for volunteer survival over the winter,” Wharton said.

“I would basically consider everything to susceptible to US 23,” he said.

“With the weather that we’ve had, with the thunderstorms and the humidity, the spores will have been moved everywhere,” said Jeff Miller, of Miller Research.

The one item of good news for growers is that the late blight US 23 strain is sensitive to Ridomil or mefenoxam, Miller said. Mefenoxam is in FRAC Group 4.

“There’s a lot of fungicides that are available,” Miller said. “We’re recommending that growers go on a seven-day schedule, every week, if they’re in a county that’s affected.”

However, if the weather stays wet or growers see more rainstorms, he advises growers to go to a five-day application schedule in this video.

By Bill Schaefer

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