No cure for disease that leaves fruit bitter, small

By DAN WHEAT

Capital Press

WENATCHEE, Wash. -- Continued grower vigilance next spring is needed to keep little cherry disease under control, a Washington State University research scientist says.

Cool, wet springs for two years in a row has increased visibility of the virus, which in warmer years mostly hides from growers, said Tim Smith, WSU Extension tree fruit specialist. Hot weather suppresses its activity.

The virus poses a potential threat to the Northwest cherry industry, Smith told growers at the North Central Washington Stone Fruit Day at the Wenatchee Convention Center on Jan. 19.

Short of cutting down trees and replanting, there is no cure for the virus, which wiped out the British Columbia cherry industry in 1933, Smith said.

"They lost 60,000 trees, which was 90 percent of their crop and had to start over," Smith said. The outbreak that spread by mealy bugs from ornamental cherry trees.

Washington, Idaho and Montana cherry trees suffered lighter damage from that outbreak.

British Columbia experienced another serious episode in the 1970s, Smith said.

In the last two or three years there have been smatterings of little cherry disease reported throughout Central Washington. The greatest concentration has been in the Wenatchee area from Malaga and Rock Island to Orondo, Smith said.

The disease was confirmed in eight orchards in that area in 2011 and in 10 in 2010, he said.

The apple mealy bug spread the disease years ago but is nearly nonexistent now, Ken Eastwell, WSU virologist in Prosser, has said. The grape mealy bug is a carrier now.

The virus also spreads through root grafting, roots from an infected tree growing into roots of surrounding trees, Smith said.

Growers cannot diagnose the disease from looking at their trees, he said. Symptoms include fruit being pinker when healthy fruit is red, about half the size of normal cherries and flat on one side, he said. But the clincher is a bitter, acid flavor. "No one wants to eat a second one," Smith said.

Usually just portions of trees are infected, so it's not uncommon to have good and bad fruit on the same tree, he said. Growers have thought weak limbs were winter damage only to find out it's the virus. It can spread rapidly within an orchard.

The best treatment is to cut down infected trees and treat the stumps with Roundup to protect neighboring trees, he said.

"Growers don't like to tear out trees, but if they wait they can lose more," Smith said. "You have to be brutal with this disease or it will spread."