Good Fruit Grower

May 15

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newly recognized virus has Washington State's wine grape industry seeing red, and not just from red blotchy leaves, symptoms of the disease. The emerging disease is frustrating to those who used certified plant material tested to be free of known viruses—and could have the new disease anyway. But it's also a learning opportunity and demon- strates the need for vigilance when it comes to grape diseases. The new virus, called grapevine red blotch-associated virus, was first recognized in 2008 in a Napa, Califor- nia, vineyard. It's so new that scientists are still learning about it. "What we do know is how to recognize it in vineyard situations," said Dr. Marc Fuchs, plant pathologist at Cornell University. Symptoms are red blotches or specks on leaves near harvest, often starting in the center and spreading out to the upper portion of the leaf. Older leaves may fall off prematurely. "A telling symptom is that the primary and secondary veins on the leaf underside turn red," he said, "but red veins by themselves are not descriptive of the virus. You have to see red specks also on the upper part of the leaf to know." Fuchs made his comments at the annual meeting of the Washington Association of Wine Grape Growers in February. Red blotch virus has been confirmed in all types of grapes and in all kinds of rootstocks from coast to coast and in Canada, he said. Although initial reports point to the disease being a North American problem, Fuchs believes that with the global movement of plant material, it will be found wherever grapes are grown. The virus has been extensively dispersed across the United States and detected in at least ten states and in two Canadian provinces. "There's little doubt that is has spread through propagation and uncontrolled use of infected grafting material," Fuchs said, but added that more research is needed to definitively identify the means of transmission. "On the East Coast, there's been no evidence of red blotch moving vine to vine or from vineyard to vineyard. But California is a different situ- ation. A few exceptions there suggest that the virus has spread." Washington State University scientists found that Virginia creeper leafhopper (Erythroneura ziczac) was capable of transmitting the virus from vine to vine under confined, greenhouse conditions. Research is needed to confirm the insect's ability to vector red blotch in the field field. The virus significantly impacts fruit quality and affects ripening. "There have been reports of Brix being reduced by five to six degrees at harvest," Fuchs said, "but so far there are no indications of effects on yields, like those of grapevine leafroll virus. The new virus also substan- tially reduces anthocyanins and tannin compounds in grapes." Scientists have developed a diagnostic assay to iden- tify the disease. Tissue samples (leaves, petioles, dormant canes, etc.) can be tested at any time during the growing season using PCR (polymerase chain reaction) assays. 42 MAY 15, 2014 GOOD FRUIT GROWER Grapes A leaf from Merlot grapevine showing red veins and red blotches on margins and interveinal regions, typical symptoms of red blotch disease. 888.638.1955 • • Parka is a trademark of Cultiva. SureSeal is a trademark of Oregon State University. Always read and follow label directions. ©2014 Cultiva. Don't let another wet spring put the damper on your profits... Reserve your Parka today. Two applications, first at straw color and a second 7 - 10 days later are all that's needed to reduce rain induced splitting on your cherries. Pick Parka today and sleep better when the black clouds roll in. For more information call Cultiva at 888.638.1955. Parka Saves Time, Money and Cherries Who'll Stop the Rain? New grape virus in Washington Don't assume that red leaves mean grapevine leafroll virus— they could be symptoms of a new disease. by Melissa Hansen Map of red leaf blotch disease detections in North America. MAP COURTESY OF MARC FUCHS, CORNELL UNIVERSITY

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