Issue link: http://read.dmtmag.com/i/459886
22 FEBRUARY 15, 2015 GOOD FRUIT GROWER www.goodfruit.com "It could be that the plants lost infection over time," he said. "Or the infection could be from environmental contamination, such as fecal matter left by leafhoppers." Bahder and the research team have been studying how the virus moves within a vineyard. They are tracking its spread in a Cabernet Sauvignon block planted in 2001 at UC Davis' Oakville Station. Since red blotch was first identified in the block in 2011, extensive testing has been under way. Testing of all vines in the block was completed last year. Researchers used a new diagnostic tool for red blotch disease called qPCR (quantitative polymerase chain reaction) to analyze the samples. Evidence shows that it can be transmitted by grafting. Preliminary analysis shows there is evidence for spread in the vineyard, but more concrete results are needed to confirm the rate of spread. It also appears there may be two genotypes or variants of red blotch. Close examination of Bahder's vineyard map that pinpoints each infected vine showed that many of the new positive finds in one particu- lar corner of the block in 2013 were of the newly identified genotype. He also found one sample had a mix of both red blotch genotypes. Bahder stressed that the two genotypes in California have not yet been compared to any genetic variance that may exist in Washington State. Clean vines Red blotch virus has been frustrating for growers who purchased cer- tified plant material, only to end up with the virus in their new plantings. When purchasing certified plant material, growers should ask which viruses have been tested for, including red blotch. Growers must also be on constant lookout for suspicious looking leaves in their vineyards. The Washington Wine Industry Foundation received specialty crop research funding to sponsor a clean plant ini- tiative and has held numerous workshops and field days to educate growers and workers about grapevine diseases. Additionally, the wine foundation has distributed a disease identification pocket field guide in Spanish and English. Washington growers who think they have disease in their vineyard can contact WSU's Dr. Naidu Rayapati at naidu.rayapti@wsu.edu. • COURTESY OF WASHINGTON STATE UNIVERSITY A Merlot grapevine shows redleaf symptoms on mature leaves in the lower portions of the canopy. Symptoms are easily confused with grapevine leafroll disease.