Good Fruit Grower

November 2013

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Rapid test needed L ittle cherry disease is not the only cause of small fruit. A variety of factors—nutrition, irrigation, crop load, and other viruses—can result in little fruit. The current method of identifying infected trees involves running leaf samples through a bioassay in a laboratory, a cumbersome, time-consuming process. Washington State University's Dr. Ken Eastwell and other scientists at WSU's Prosser research station have been working to develop a rapid test for little cherry virus 2. Last year, WSU partnered with a private company to develop a 30-minute test that could be run in field offices. However, the company decided not to commercialize the technique due to inadequate market size. Eastwell is now putting the test components together and hopes to have a method ready soon that can be used in the field (or grower's office). In the past, cherry growers weren't that concerned with little cherry disease and funding for broad scale research was not available, he said. But the recent spread of the disease and its severity has the attention of the cherry industry. —M. Hansen Eastwell said because mealybugs don't usually cause an economic impact in cherries, few growers follow a spray program aimed at mealybug. Compounding the difficulty of mealybug control are the different life cycles of the two pests. Apple mealybug has one generation per year, while grape mealybug has two, requiring different spray timing for the two species. Some things are known about the virus, said Smith, who works with tree fruit growers in north central Washington. It's not spread through pollen, or mechanical means like pruning. It needs physical, tree-to-tree contact, which is why root grafting is one means of transmission. Vectors carrying the disease from tree to tree is the other means, he said. "But we still don't have a good handle on how rapidly the virus is spreading," Eastwell said. Beers agrees. "We need more information on how widespread grape and apple mealybug populations are, region by region," she said. "We have little information following the disease in an orchard. We have way more questions than answers." Eastwell and Beers are teaming up in a transdisciplinary project to learn more about the virus and vectors. Baseline data was collected last summer from an infected orchard and the researchers are following its spread within the block. They also hope to work together on a research project designed to develop disease management strategies for growers. Eastwell recommends that when removing a tree, growers cut it three feet above the ground and apply herbicide to the freshly cut tree. The herbicide application will kill any root suckers and help identify nearby rootgrafted trees that will also need to be removed. For growers who cannot burn but must chip trees, there is concern that mealybug could survive the chipping process, he warned. "So be sure to spread the chips in a nonhost location. "And always replant with certified trees," Eastwell stressed. • www.goodfruit.com Good Fruit Grower NOVEMBER 2013 15

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