Issue link: https://read.dmtmag.com/i/506700
www.goodfruit.com GOOD FRUIT GROWER MAY 15, 2015 11 Disease has hidden costs R ick Hamman of Hogue Ranches in Prosser, Washington, says the losses from grapevine leafroll disease estimated in the Washington State University study by agricultural economists are real, though they are often hidden from growers. "These are real numbers, and they do hurt your pocketbook," said the viticulture manager. "A lot of times, you don't really see the numbers because you tolerate and live with the disease." Hamman, who helped validate grape production costs used in the economic study on leafroll disease, has firsthand experience with what he calls a "virus tax." In the last ten years, he's been involved with replanting eight blocks infected with leafroll and other diseases. He says there are hidden costs involved with replanting, including demolition costs of pulling out trellis posts and wires and digging out roots that could harbor disease. Moreover, it takes three years before a replanted vineyard returns to full production. "That's why it's very important to use only clean plants," Hamman said. "And you probably need to test plant material even if it's certified. We bought certified Chardonnay Clone 37 from a California nursery, and in the second leaf I noticed we had funny colored leaves, which I initially thought was related to potassium deficiency." But what really got his attention was when sugar levels in the block seemed stuck and never rose above 21° Brix, even four weeks after everything else was har- vested. Eventually, leafroll disease was confirmed in the eight-acre block, but only after wood was used to propagate a second five-acre block. Both blocks had to be removed. He believes losses from leafroll disease hit a small grower with limited acreage even harder than one who has several different blocks and can better absorb a hit to operating revenue. —M. Hansen your pocketbook? reduction scenarios—a loss of 0.4° and 1.0° Brix. Assuming a 20-year life span for a healthy Merlot vineyard, the Net Present Value (NPV) approach was used to estimate the operating return that would be lost due to leafroll disease. (NPV is a method of analyz- ing future cash flows. The overriding concept is $100 today is worth more than $100 ten years from now, because of the time value of money. NPV accounts for the time factor and brings all future cash flows to the present.) In the best case scenario, a grower experi- encing 10 percent decrease in yield and 0.4° Brix decrease would lose an estimated $3,005 per acre over the 20-year span of the vineyard. The estimated loss for the worst case scenario of 30 percent yield decline and 1.0° Brix decrease was $19,800 per acre over the 20-year period. (See Figure 2.) For the first time, the data gen- erated from this project provide reliable estimates of crop losses in Merlot and sci- ence-based information on how grape leafroll disease can impact growers' operating income in Washington vineyards. The results from this study indicated that reduction in fruit yield and quality due to leafroll infec- tion is real, tangible, and significant. It is important to note that, even at a minimum loss of 10 percent yield, leafroll does impact a grower's pocketbook negatively over the life of a vineyard. Although this study is confined to one cultivar, it is likely that leafroll disease can cause substantial eco- nomic impact to other wine grape cultivars. Preliminary analysis of the economic impact of red blotch in Merlot also indicates that the disease could cause substantial losses to growers' operating returns. The research team is currently extending these studies to determine economic impacts and financial implications of viral diseases in other wine grape cultivars. In addition to estimating operat- ing returns lost due to viral diseases, the team will be assessing the eco- nomic benefits of implementing control strategies such as roguing, or removing virus-infected vines, and vector control and to iden- tify economic thresholds (when losses due to viral infections in a vineyard exceed operating returns) of viral diseases to help growers decide when to replant vines or replace infected vineyards. A clear articulation of the financial benefits of management of viral diseases will promote rapid adoption of best management practices by grow- ers and strengthen industry efforts in advancing clean plants for healthy vineyards. • CHRIS BEAVER/WSU Merlot wine made from grape leafroll- infected fruit was lighter colored than wine from uninfected Merlot grapes of the same block. 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