Good Fruit Grower

February 15

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18 FEBRUARY 15, 2014 GOOD FRUIT GROWER (Continued from page 16) Western X phytoplasma Eastwell reported that there's been a significant increase in the last few years in Western X in Washing- ton orchards, particularly in southern cherry- producing regions of the state. Peach trees are the primary host, although it can severely impact cherries. During a statewide peach tree survey in the 1940s, Western X was found mostly in Asotin, Ferry, Garfi eld, Grant, Whitman, and Stevens counties. In Benton County, .03 percent of trees were infected near Prosser, but near White Bluffs, almost 13 percent were infected. During the peach tree survey, the disease was found to be most prevalent near virgin, sagebrush, and desert land. Western X was fi rst diagnosed in Washington cherry trees in 1946. A survey conducted in 1947 found nearly 1,500 infected trees out of about 170,000 inspected. Symptoms spread slowly through the tree but quickly through an orchard. Fruit from infected trees are small, pale, and bitter tasting. "With Western X, the fruit doesn't just taste insipid as with little cherry virus, it tastes bad," Eastwell said. Mahaleb rootstock appears to be hypersensitive to Western X. In California, where Mahaleb is commonly used, trees can die within nine months of infection. In Washington, infected trees usually take two years to die from the disease. In California, where most of the transmission data comes from, cherry leafhopper and sharp-nosed leafhop- per appear to pick up the disease from weeds and then transmit it from tree to tree, he reported. "We don't have cherry and sharp-nosed leafhoppers in Washington, but we do have mountain leafhopper, the major vector here." Leafhoppers overwinter on winter annual weeds near water, with adults migrating to orchard weeds in late spring. "The leafhopper doesn't really like cherries, but, like a port in a storm, it will colonize if that's the only plant available," Eastwell explained. In Washington, scientists believe that leafhoppers bring the disease into the orchard from nearby weeds. The plant host list is extensive and includes alfalfa, Cal- ifornia burclover, clovers, curly dock, dandelion, sweet clovers, and several vetches. "In California, it appears to spread from cherry tree to cherry tree," said Eastwell. "But I'm not sure that is true here in Washington." He added that peach trees are a dead-end host, and there's been no evidence that cherry trees are picking up disease from peach trees. • Consider for your next planting: • BRUCE PONDER • SUSAN WILKINSON • ADAM WEIL • DAVE WEIL 503-538-2131 • FAX: 503-538-7616 BENEFITS: • Disease tolerant • Cold hardy • Adapts well to all cherry-growing districts • Forms flower buds and comes into bearing quicker than Mazzard with a better distribution of flower buds Roots available for SPRING DELIVERY Call Tree Connection: 800-421-4001 Dwarfing Cherry Rootstock Krymsk ® 5 Krymsk ® 6 [cv. VSL-2, USPP 15,723] [cv. LC-52, USPP 16,114] "Krymsk ® 5 and Krymsk ® 6 cherry rootstocks have proven to be the best rootstock for our orchards. They are yield efficient, grow and adapt well, and are cold hardy." —John Morton The Dalles, Oregon T he appearance of little cherry diseases calls for aggressive action, says Dr. Ken Eastwell, plant pathologist for Washington State University. "When it comes to little cherry diseases, inaction is not an answer," he said, adding that the disease can spread from infected trees to adjacent trees and neighboring orchards, causing severe economic impact. How fast the disease spreads depends on the level of disease management. "You need to remove trees as soon as you see symptoms, keeping them contained as they're taken out of the orchard," he warned. "If infected trees are left in the orchard, disease incidence increases greatly." He advises growers, when roguing trees, to kill vectors infesting the diseased trees so they are not spread throughout the orchard as trees are removed. Spray diseased trees with the appropriate insecticide seven days before cutting them down. Eastwell offered the following suggestions for managing little cherry disease: Little cherry virus 2 1. Plant only virus-free trees, including pollinators. 2. Remove symptomatic trees, being wary of root grafting, and replant with clean stock. (Remove entire orchard if more than 10 percent trees are infected). 3. Take care when removing trees to avoid spreading vectors throughout orchard. 4. When replanting, remove bitter cherry plants near the orchard. 5. Control apple and grape mealybug vectors in orchard. Little cherry virus 1 1. Plant only virus-free trees, including pollinators. 2. Rogue infected trees based on economic impact. 3. No vector has been identifi ed. Western X phytoplasma 1. Plant only virus-free trees, including pollinators. 2. Manage nearby ornamental hosts of choke- cherry and bitter cherry, removing or treating with insecticide. 3. Treat orchard for leafhopper vectors, using delayed dormant oil sprays and insect control until leaf drop. 4. Control weeds that harbor leafhoppers and phytoplasma. —M. Hansen DISEASES require action "When you have small fruit, it means that something is interfering with the vascular system of the tree." —Ken Eastwell PLAY scan to watch Diseases & Disorders

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