Block grant to support affordable testing to fight little cherry disease

Cherry trees infected with little cherry disease bear small, bitter or bland fruits that often lack attractive coloring.

Washington State University will help Washington cherry growers test more trees for the damaging little cherry disease thanks to a Washington State Department of Agriculture Specialty Crop Block Grant received by the Washington State Tree Fruit Association.

Named for its most distinct symptom—small, colorless fruit—what growers call ‘little cherry’ is a simultaneous outbreak of little cherry virus-2 and the X-disease phytoplasma, both of which produce similar symptoms on infected cherry trees and are difficult to tell apart, even by experts. This is more difficult because symptoms are usually noticed only a few weeks before harvest.

The pathogens are spread in orchards by small insects: the virus by mealybugs, and the phytoplasma by leafhoppers.

Tests are available for growers to learn if a tree is infected, but they can be expensive. The new three-year, $530,000 grant will help to expand testing capacity at WSU’s Plant Disease Diagnostic Lab in Pullman with more equipment and supplies. This support will reduce testing fees by approximately 50%, to $50 per test.

“Affordable and available testing is a key element of our industry’s response to little cherry disease” said Jon DeVaney, WSTFA President. “Washington’s cherry growers appreciate the support of the WSDA Specialty Crop Block Grant Program and WSU’s Plant Disease Diagnostic Lab in this effort.”

“Active, aggressive tree removal is the best way to suppress this outbreak and prevent further spread, and testing is an essential tool to identify trees in the early stages of infection,” said Scott Harper, WSU virologist and director of the Clean Plant Center Northwest. “It will help growers make informed management decisions for their orchards.”

Harper’s lab supported the initial wave of testing in 2018-2019, and commercial labs took over testing in 2020, but few growers could afford to test every tree that they suspected might be infected.

“WSU and collaborating laboratories are working hard to provide growers with little cherry testing services,” said Tianna DuPont, a WSU Tree Fruit Extension Specialist. “Additional support for the WSU Plant diagnostic lab is essential to provide sustainable robust public diagnostics so growers can identify and quickly manage the multiple problems that attack their trees.”

Removing infected trees quickly is the best way to fight the disease, as there is no treatment and early removal can limit spread of the virus to nearby trees in an orchard, Harper said. Testing also helps avoid removing a tree exhibiting symptoms that look like the disease, but isn’t infected with little cherry pathogens.

WSU tree fruit scientists work closely with growers to fight diseases and support the Washington cherry industry, which produces more sweet cherries than any other state.