One of the best management strategies wine grape growers have to manage vines infected with grapevine leafroll disease is to rogue them out of the vineyard, but growers face an unknown question: What is the economic cost to this strategy over the long term?
Trent Ball, agriculture department chair at Yakima Valley College, aimed to answer that question by examining the on-farm costs of vine removal, factoring in the rate of spread, compared with a do-nothing approach, and the resulting impacts to grape and wine yield and quality.
Then, Ball compared these costs over time. “It’s not just what it would cost me next year. This roguing strategy is something you would do over time, that’s perpetual,” he said at the Washington Winegrowers conference in February. For that reason, Ball said, the study examined the cost on an annual basis over a period of 20 years.
If one of the best management strategies is to rogue infected vines, is it financially viable over the long term?
Recent research by Washington State University plant pathologist Naidu Rayapati, director of WSU’s Irrigated Agriculture Research and Extension Center, has shown grapevine leafroll disease can spread very quickly, infecting more than 50 percent of a Washington vineyard in just a couple of years, or slowly over time. Management practices vary depending on the rate of spread at a specific site.
Yields also fall on average by about 20 percent for leafroll-infected vines. However, grapes also could see a Brix reduction. “The quality implications can be significant as well,” Ball said. “Based on your contract with your buyer, you may have a Brix minimum — 23.5 on red is typical — and there can be a penalty for any Brix below that.”
Generally, growers should be scouting for disease in the fall, identifying those vines that look infected and testing and removing those infected vines in the winter.
For Ball’s analysis, roguing costs ranged from $10 to $16 per vine. Included in those figures were the costs for scouting and testing for disease, vine removal, replanting followed by vine training in year two, and special irrigation that might be required to accommodate a young, new vine in an older vineyard (see Figure 1).