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Little cherry disease on the rise

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Dan Wheat
A disease that causes small, bitter cherries is increasing in Washington and growers need to take it seriously before it "takes out the industry," a scientist warns.

WENATCHEE, Wash. — Little cherry disease is threatening the Washington cherry industry and growers need to take it seriously, a Washington State University research scientist says.

The virus, which results in small, bitter-tasting cherries that are unmarketable, took a big jump in 2013, Tim Smith, WSU Extension tree fruit specialist, told growers at North Central Washington Stone Fruit Day, Jan. 21.

The meeting was sponsored by WSU Extension and the Washington State Fruit Commission and was held at the Wenatchee Convention Center.

“I’m not sure everyone recognizes how serious it is,” Smith said of the disease. “We need to jump on it now and get ahead of it before it takes out the industry.”

There is no cure and the only treatment is tree removal, he said. Fieldmen at Stemilt Growers Inc. were “getting very good at spotting it” last fall and 200 acres of cherry trees were yanked out on Stemilt Hill and Wenatchee Heights, Smith said.

“I would guess another 200 to 400 acres need to come out in the Wenatchee area,” he said. “Malaga has taken out a patch or two. Had they not, they would be in serious trouble by now.”

The virus is difficult to detect because it’s only visible at harvest when growers are “busy doing 100 other things,” Smith said. The tree looks fine, but cherries on an edge or part of a tree aren’t ripe, he said. They finally turn red, but never taste good and are always small and sometimes heart-shaped, he said.

Growers are busy so they don’t notice or if they do they think it’s just an oddity that will be gone the next year, Smith said. But they need to stop and mark those trees and check them out when they have more time, he said.

It’s difficult to detect in Bing and Sweetheart, Washington’s most common varieties, and the disease spreads rapidly, seeming to “cross an orchard in lickety-split time,” he said. Fumigating the ground after tree removal doesn’t help so its best to let ground lie fallow for a year and watch trees that are left, he said.

The disease is spread by mealy bugs and by roots of trees grafting into each other, Smith said.

The Washington Tree Fruit Research Commission and Oregon Sweet Cherry Commission agreed in December to spend $63,479 in the first of three years of study to find out why it is increasing and develop management strategies.

In 1933, the virus all but wiped out the British Columbia cherry industry and 60,000 trees, 90 percent of the total, were removed, Smith has previously said. British Columbia experienced another serious episode in the 1970s.

It’s been detected in Washington since the 1930s but has never been a serious problem, he told the growers. Wet, cool springs, he believes, contributed to an uptick in 2010 and 2011.

In 2010, Smith confirmed the disease in 10 out of 10 orchards he suspected. In 2011, it was eight out of eight and in 2012, it was three out of six. “In 2013, we had many suspected orchards. Too many for me to count,” he said. “Almost all were tested and confirmed.”

It’s known to be throughout Central Washington and in Hood River, Ore., he said.

Contacted later, Kyle Mathison, vice president of Stemilt Growers Inc. and president of Kyle Mathison Orchards, said he removed more than 100 acres on Stemilt Hill and Wenatchee Heights in 2013 and that several other growers made up the rest of the 200-acre removal. He owns hundreds more acres in the vicinity and said he’s worried.

“You have to bite the bullet and take them out and start over,” he said. “Hopefully we won’t have reinfection. That’s our biggest concern. The economic loss is way bigger than a rainstorm or hailstorm because you have to wait five to six years to get back into production. It’s just devastating.”

Ken Eastwell, a WSU plant pathologist in Prosser, said the disease is a significant concern but manageable with effective control of mealy bugs and tree removal. It appears to be most prominent in Wenatchee perhaps because mealy bugs prefer apples and pears and there are a lot of cherries in close proximity to apples and pears, he said.

Mealy bugs are increasing for several reasons including softer, more targeted pesticides, he said. Older, harsher chemistries used for cherry fruit fly were perfectly timed to hit apple mealy bugs, he said.



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