Good Fruit Grower

October 2012

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Grapes Clean vines keep viruses out A lot goes into making sure growers have access to clean planting material. by Melissa Hansen ashington State's grape industry teamed up with researchers and regula- tory officials last summer to educate growers and vintners about the importance of clean plants and about the process of certifying plant materials. Grapevine leafroll disease and other viruses have become a serious problem in Washington vineyards in recent years for several reasons: shortage of certified plant material during grape planting booms, spread of disease into clean vineyards from vectors like grape mealybug, improved technology that detects viruses better, and aging vineyards susceptible to crown gall. Grape leafroll disease is economically important, because it reduces vine vigor, affecting yield and quality of grapes, and can delay fruit ripening. This year's grape field day held in August and sponsored by the Washington Association of Wine Grape Growers included demonstrations of how grape plant tissue is analyzed for viruses, how plant selections are screened for diseases, and how selections are propagated for planting in the foundation block housed at Washington State University's Irrigated Agriculture Research and Extension Cen- ter in Prosser. The day included visits to a custom budwood nursery, the state's largest certified grape nursery, and a tour of the teaching vineyard and winery of Yakima Valley Community College's vineyard and winery technology program. Regulatory support For more than 40 years, the state agri- culture department has implemented a certification program to provide grape growers with access to clean plant mate- rial. Inspection by state officials is required of all plant material brought into the state to protect established vineyards from unwanted diseases and pests like phylloxera. As part of the certification program, mother blocks at certified nurs- eries are registered with the state; depart- ment of agriculture officials inspect the blocks twice a year to look for signs of virus and test vines with suspicious symp- toms. The state also conducts random testing of mother block vines. New grapevine selections are brought into the state through the Clean Plant Center-Northwest Grapes to be tested and indexed of virus. The center provides quarantine services for grapes, along with centers for tree fruit and hops. Facilities for all three crops are located at WSU's research station in Prosser. After grape selections are cleared of virus, a process that can take two to three years, they are planted in the registered foundation block, also maintained by the Clean Plant Center. Commercial nurseries obtain cuttings and budwood from the registered vines for planting in their mother blocks. Each vine in a mother block must be traced to a single vine in the foundation block as part of the certification process. In addition to being planted in the foundation block, one vine of each selec- tion is also grown in a screenhouse at WSU for protection against vectors and winter injury. It can take four to five years from the time the selection screening process begins to the time when budwood is dis- tributed to commercial nurseries for propagation. New testing But even the certified program has not been foolproof, says Tom Wessels of the Washington State Department of Agricul- ture. "We're always playing catch-up," he said explaining the program during a tour of the Clean Plant Center. "Some of these mother blocks from the 1970s that we Gary Ballard worries that contaminated soils can infect clean plants. PLANT IN CLEAN ground clean plant material can quickly be undone by planting in dirty soil, says manager Gary Ballard. For nearly a decade, Ballard has managed the grape program at Clean Plant G A Growing Legacy Sinc A Growing Legacy Since 1816 or Shawn Debi D ella 36 OCTOBER 2012 GOOD FRUIT GROWER Stark Bro's Nurseries & Orchards Co. Center-Northwest Grapes (formerly the Northwest Grape Foundation Service), overseeing the quarantine testing procedures and maintenance of the four-acre grape foundation block. Since the grape foundation program was re-invigorated in the early 2000s, more than 325 grape selections have gone through the quarantine program, with 32 selections entered this year. Any grower can arrange for a selection to come into the program. The process is virtually free if the selection will be made public. Fees for exclusive selections can run into the thousands of dollars when years of maintenance in the foundation block are accounted for, said Dr. Markus Keller of Washington State University. No other grape certification program indexes for crown gall, Ballard said, which makes the Northwest program the cleanest in the nation. "There's no agribacterium in any of the plant material that goes into the founda- tion block," he said emphatically. "But it's easy for a grower to compromise the no- crown-gall status by planting in dirty ground. Growers need to realize how easy it is to take years of work and throw it away by being careless." Grape leafroll disease has been known to move into even clean vineyards, Ballard said, adding that grape mealybug, a known vector, can bring the disease into the vineyard by hitchhiking on equipment, clothes, and riding the wind. "But if you start clean, with certified vines, you can at least slow up the progression of the disease." —M. Hansen rape selections that come out of the Clean Plant Center-Northwest Grapes are certified to be free of known grape viruses and crown gall disease, making them the cleanest in the nation. But years of work to test and maintain the Photo by Melissa hansen

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