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Fire blight grows worse in Okanogan

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Dan Wheat
An apple and pear tree-killing bacteria occurred in Honeycrisp in 2013 and was worse in the northern part of Central Washington while declining in the south.

WENATCHEE, Wash. — Fire blight, a bacteria that kills apple and pear trees, was worse in the northern part of Central Washington in 2013 and was found in Honeycrisp apple trees, a scientist who tracks it says.

“We’re starting to get ahead of it in the Tri-Cities and Yakima (the south) but it was worse in the north,” Tim Smith, Washington State University Extension tree fruit specialist and plant pathologist, told growers at North Central Washington Apple Day.

The meeting at the Wenatchee Convention Center, Jan. 23, was sponsored by WSU Extension and the North Central Washington Fieldmen’s Association.

The bacteria overwinters in trees and reactivates in oozing cankers around blossom time. It attracts flies and other insects that spread it to blossoms. Within a week or two, infection is ahead of portions of the tree that show withering.

It was once only a concern in pears but has been a concern in apples since 1993, with 1997 and 2012 being the worst years, Smith wrote in a 2012 paper. Thousands of acres of older Gala and Fuji apples were blighted in 2012 when rain followed a late April warming, he wrote.

Temperatures rising to 94 in late April and then falling to 52 with rain contributed to its spread in 2013, he said at Apple Day.

More thunderstorms than usual whipped trees causing minor wounds on fruit tips and new wood that presented more area for bacteria to grow, he said.

“Okanogan County (in the north) had fire blight on many different crops. We found out Honeycrisp is susceptible to fire blight. They are planting a lot of it up there and they found it on them,” Smith said.

On the whole, the fire blight problem in Central Washington is improving and it is manageable, he said. Antibiotics, copper fungicides, minerals and biological controls are used. No perfect tool has been found, he said.

Infected portions of trees should be cut out when spotted instead of waiting until winter, he said. Cleaning clippers between trees with soap and water hasn’t been proven to help but makes sense, he said.

Fire blight started in southeastern Canada and spread to other parts of the world, Smith said. New Zealand is the only Southern Hemisphere country with it, he said.

All the “-stan” countries — like Afghanistan and Kazakhstan — have it and are where apples originated, he said.

“Our (WSU) breeding program is looking at some strains of apples from that region to find fire blight resistance. We should be able to find some and use them in our breeding,” he said. Crab apple is resistant but tastes bad, he said.

From the “-stans” it’s likely to spread to China, where it could be a big problem for millions of small apple growers, he said.



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