Issue link: https://read.dmtmag.com/i/314286
www.goodfruit.com GOOD FRUIT GROWER JUNE 2014 37 advantageous to rogue infected plants versus removing the entire vineyard and starting over. The study is based on yield and quality data collected from a commercial Merlot vineyard from 2008 to 2012 by Rayapati. Preliminary numbers show annual yield losses due to the virus ranging from 12 to 28 percent, with an average loss of 18 percent and Brix reductions ranging from 4 to 8 percent. Using operating cost numbers provided by growers and an average yield of 4.5 tons per acre valued at $1,127 per ton, Ball calculated the economic return per acre. The return did not include fixed costs such as management, land costs, depreciation, and interest. Under this scenario, a Merlot block with no leafroll virus returned $2,683 per acre; the same block with a 10 percent yield reduction returned $2,224 per acre. A yield reduction of 30 percent resulted in $1,377 per acre less return than the noninfected vines. Ball is expanding the analysis to include the economic impact from declining quality, noting that many winery contracts set a minimum Brix and implement price penalties if grapes don't meet minimums. Also, he's extending his analysis to reflect the long-term life of a vineyard, while considering management tools of roguing infected vines and replanting. "Ultimately, we want to learn when the economic impact from grapevine leafroll virus is high enough to warrant removing the entire vineyard," he said. Mimi Nye, vineyard manager of Ste. Michelle Wine Estates's Canoe Ridge Estate, shared her experiences of trying to manage leafroll virus while striving to produce world-class grapes. "I've been vineyard manager since Canoe Ridge Estates was planted in 1991," she said. "Imagine my horror when we discovered grapevine leafroll virus." Symptoms were first noticed ten years after planting the 63-acre block of Caber- net Sauvignon near Paterson, Washington, but Nye thinks the disease was there in the beginning. "We just weren't scouting for it." Vine removal costs include a three-person crew to use a front-end loader and pull out each vine. It works out to $132 per acre or 18 cents per vine, according to Rick Hamman. PHOTOS COURTESY OF RICK HAMMAN VAPOR GARD ® FOR CHERRIES AND APPLES SEE LABEL FOR ADDITIONAL INFORMATION AND ALWAYS READ AND FOLLOW LABEL DIRECTIONS N o G en e r i c S ub s ti t u t e ! A CONSISTENT PERFORMER CONFIDENCE Comes from 40 years and over 150,000 acres treated with VAPOR GARD. That's why many Growers, Consultants, Pest Control Advisors and Packing Houses understand VAPOR GARD's BENEFITS and VALUE on CHERRIES. 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I see that my cherries stay firmer longer with Vapor Gard. Vapor G ard has more benefits than just rain protection." LIVING WITH grapevine leafroll virus T he best way to manage grapevine leafroll virus is to remove infected vines annu- ally and control the grape mealybug vector, says the vineyard manager of Canoe Ridge Estates near Paterson, Washington. Mimi Nye gives the following tips for managing leafroll virus in a wine grape vineyard: 1 Scout red varieties and randomly test whites. Red leaf symptoms in red wine grapes are most easily observed in September. If you wait too long in the fall, it becomes hard to distinguish symptoms from a natural change in leaf color. Random testing in white varieties is suggested because symptoms are subtle and difficult to detect. 2 Tag suspected vines. She tags vines with colored zip ties, using a different color for each year. If you have to go back in that area again, you'll be able to see if the virus is spreading to other vines. 3 Test suspected vines. Test the suspicious vine to confirm infection. Contact Dr. Naidu Rayapati, Washington State University scientist, for assistance. 4 Use visuals to teach scouters. Show workers and scouters photos of infected vines and leaves and also show them examples in the vineyards. It's not enough to show one leaf. Know what other factors can cause red leaves. 5 Remove infected plants to stop spread of virus. 6 Replants need extra water. She uses larger drip emitters on the replanted vines, and even runs a PVC pipe down to the root to ensure enough water is getting to the roots. 7 Monitor and control mealybug and scale vectors. 8 Practice sanitation measures to prevent spread of vectors. Use separate tools for clean and infected blocks; wash equipment when moving from infected to clean blocks; don't move field crews from infected to clean blocks on the same day. —M. Hansen