Miserable weather may fuel destructive disease
By DAN WHEAT
Washington cherry growers say they are worried about fruit size and little cherry disease as they continue dealing with too much cool weather.
Cumulative lack of heat leads to poor cell division and smaller fruit. It also increases the likelihood of little cherry disease, a virus that leaves small, misshapen fruit of poor flavor and color.
Washington State University AgWeatherNet stations in Yakima and Manson show the coldest spring since 2003, said Jim Holcomb, meteorologist at Clearwest Inc., Wenatchee.
"Overall, you have to go back to 1955 to find a spring (March through May) as cold as this one," he said.
Wenatchee's average daytime high in May is 73 degrees but it had been about seven degrees lower this year, Holcomb said on May 26.
Growers in the southern part of the state report good cell division, said B.J. Thurlby, president of Northwest Cherry Growers in Yakima.
"Some are seeing 11 row, which is pretty good. They'll get larger," he said.
Cherry size is measured by the number of cherries in a row in a 20-pound box. Large cherries get up to 8 row. Small is 12 and 13 row.
Ken Eastwell, a virologist at the Washington State University Irrigated Agriculture Research and Extension Center in Prosser, said little cherry disease is a big concern.
"It's what wiped out a large portion of the industry in British Columbia in the 1940s and '50s and impacted Washington, Idaho and Montana," he said.
It was transmitted by the apple mealy bug back then. That pest is almost nonexistent now but has been replaced by the grape mealy bug, he said.
"We don't know yet if the grape mealy bug will transmit the virus but we know closely related viruses are transmitted by a wide variety of bugs," Eastwell said.
Mealy bugs can be combated with pesticides but once a tree is infested with the virus, removal is the best remedy, he said.
"Last year, it reached a point it couldn't be ignored anymore," he said.
He knew of 40 orchards with a portion of their cherries too small to market last year. About half had that virus and a quarter had other viruses, he said.
Thurlby said the impact of little cherry disease is relatively small but that growers fear it could expand. Viruses were much on the minds of growers at a May 25 meeting, he said.
Lambert, Sam and Deacon -- all older varieties -- are most susceptible to little cherry disease but it occurs in Bing and Sweetheart, Eastwell said.
It isn't noticeable until cherries reach straw stage, turning from green to pink, he said.
It was most prevalent in the Wenatchee area last year, said Mike Bush, WSU tree fruit specialist in Yakima.
Harold Schell, horticultural manager of Chelan Fruit Cooperative, said he doesn't believe little cherry disease is widespread. He said he's more worried about getting heat to build size but that so far size and cluster set look good.
"Cherries can gain size later, so if the weather improves we are in good shape for hitting size," he said.
The jury is still out on winter freeze damage, he said. The question is how much fruit will prematurely drop from trees when the weather warms.
"We came pretty close to having this whole industry rocked back on its heels pretty hard, cherries, apples and pears," he said.