'Bing' cherries a few days before harvest. The cherries on right are from a tree infected with Little Cherry Virus 2; the cherries on the left are from a neighboring (normal) tree.
How to Sample for Little Cherry Disease
Trees showing signs of Little Cherry Disease (LCD) should be flagged when symptoms are evident. The best time to see obvious LCD symptoms is a few days prior to harvest, although they may appear several weeks before harvest. While you should to mark the tree when symptoms are evident, it can be sampled later in the summer. Not all limbs show the same degree of symptoms; mark the most symptomatic limbs for sampling.
A total of 10 leaves per tree should be collected from symptomatic limbs. Place the leaves Ziploc bag, and label the bag with the orchard information. Keep the leaf sample on ice or refrigerated until testing can be completed. Dry, brittle leaves are not acceptable samples, regardless of age. If sending multiple samples, make sure the label on the bag clearly distinguishes the sample contents.
Send samples to Clean Plant Center NW for testing
Samples can be sent to:
Clean Plant Center Northwest/Hamilton Hall
Prosser Irrigated Agriculture Research & Extension Center
24106 N Bunn Rd. Prosser, WA 99350-8694
Attn. Tina Vasile
Contact for the lab is Tina Vasile, 509-786-9382 (http://healthyplants.wsu.edu/elisa-lab/). Drop the samples off at Prosser, or send them via overnight mail in a Styrofoam shipping container with an ice pack, to the address listed above. Be sure to include your name and contact information with the package. Avoid sending samples on Thursday or Friday.
Using PCR methods, the lab can test for all three LCD causing pathogens: Little Cherry Virus 1 (LChV1), Little Cherry Virus 2 (LChV2), and Western X (WX). However, testing for multiple pathogens might cost more than testing for a single pathogen. Check with the lab for details of testing costs.
What is Little Cherry Disease?
Little cherry disease (LCD) is caused by one or more of three pathogens and all are known to occur in Washington State: Little cherry virus 1 (LChV1), Little cherry virus 2 (LChV2), or Western X phytoplasma (WX). Trees with LCD produce cherries of small size and poor color and flavor making the fruit unmarketable. Little cherry disease became a statewide problem in 2010 and has since resulted in unpicked limbs/trees, tree removal, and even orchard removal. While the exact amount of infected acreage in Washington is unknown, LCD has been verified in commercial sweet cherry orchards in Grant, Chelan, Douglas, Yakima, Benton, and Okanogan counties.
How does it spread?
Little Cherry Virus 2 is spread from tree to tree by the apple mealybug (Phenacoccus aceris (Signoret)), and the grape mealybug (Pseudococcus maritimus (Ehrhorn)). Both mealybug species can be found in sweet cherry orchards in North Central Washington, and their presence has been verified in LChV2 infected orchards. However, the natural rate of mealybug movement between trees, and hence their role in the epidemiology of this disease is poorly understood. The virus is also readily transmitted by all types of grafting.
Little Cherry Virus 1 can be spread by propagation. The insect vector is not known. Some species of ornamental or wild flowering cherries can be symptomless carriers of the disease.
Western X phytoplasma is primarily spread by a leafhopper, and can occur in sweet and sour cherries, peaches, and nectarines.
It has not been demonstrated that any of the LCD causing pathogens are spread by pollen, seed, in the soil, or via pruning tools.
Developing a Management Strategy for Little Cherry Disease
NEW: Presentation now available on PDF.