As the cherry harvest wraps up, growers in Central Washington should launch their leafhopper control programs, reducing the risk of the insects spreading the Western X phytoplasma which causes little cherry disease.

That’s the message from the Cherry Institute board, which sent an email to members urging them to take the threat from leafhoppers seriously.

“Western X disease is on the rampage throughout the Yakima Valley, Mid- and Upper Valley, and the Columbia Basin,” according to the Institute news release. “The only way to control the spread of Western X is to kill the vectors (leafhoppers) and remove infected trees that serve as a source for the spread of the disease.”

Pasco-area grower Denny Hayden is one of the Cherry Institute board members sounding the alarm. He said he’s concerned, after talking with growers and fieldmen, that not enough were preparing to mount an aggressive vector control program.

“I think most people don’t appreciate the gravity of the situation,” he said, despite how much little cherry disease was discussed at winter meetings. “We’re trying to get the word out that we need to start covering these things postharvest through November.”

One postharvest spray won’t cut it, Hayden said.

Craig Harris, a Yakima Valley grower who has been battling Western X for several years, said that last year leafhopper populations persisted in the orchard until November, and, from California growers who have battled Western X for many years, he’s heard that fall sprays are key.

“We’re going on four years of removing trees and it’s still spreading. Removing the trees isn’t enough, we need to control the vector,” Harris said. He joined Hayden in urging other growers to adopt aggressive spray programs right away — with the guidance from crop consultants. That’s in addition to pulling symptomatic and infected trees.

There are lots of unknowns remaining about how best to control leafhoppers, such as the best targeted chemistries, life cycle and timing. Washington State University entomologist Tobin Northfield has undertaken studies to answer those questions, but growers can’t afford to wait for that guidance, Harris said.

Northfield is one of many researchers participating in the Little Cherry Disease Task Force (see related story: Big response for little cherry disease) that’s brought industry, science and policy experts together to find solutions to the problems posed by Western X and little cherry virus 2, which is the main vector of little cherry disease in Northern Washington and is spread by mealybugs.

That task force is doing great work, Hayden said, but he stressed that there are things growers can do right now, such as spray for leafhoppers every two to three weeks until they go dormant.

“It’s a lot more extended coverage than we’ve ever dealt with,” Hayden said. “But it’s at epidemic levels at this point in time and we’ve got a very short term to get our arms around it before it replants our industry.”

More information can be found on the WSU extension website: treefruit.wsu.edu/crop-protection/disease-management/western-x/ and http://treefruit.wsu.edu/crop-protection/disease-management/little-cherry-disease/

—Kate Prengaman