Issue link: https://read.dmtmag.com/i/506700
10 MAY 15, 2015 GOOD FRUIT GROWER www.goodfruit.com T he Washington State grape and wine indus- try has recognized management of viral diseases as one of the highest priorities if the industry is to maintain its growth trajectory. Viral diseases affect vine health, fruit yield, and quality and lead to poor quality wines. Thus, the industry must instill concerted and collaborative approaches among the stakeholders, researchers, and regulatory agencies to thwart the increasing threat of viral diseases in vineyards. This is of paramount importance for advancing sustainable growth of an industry that continues t o m a k e s i g n i f i c a n t contributions to the state economy. One aspect of viral diseases that remains unresolved is the effect that they can have on the prof- itability and sustainability of Washington's vineyards. To address this question, a project was funded by the Washington State Department of Agriculture's Specialty Crop Block Grant Program to determine the economic impacts of viral diseases on growers' pocketbooks. Washington State University scientists teamed up with agricultural economists, Trent Ball and Ray Folwell of Agri-Business Consultants, to estimate the operating returns lost by a grower due to viral diseases. The team has initially focused on the economic impact of grapevine leafroll disease, by far the most insidious viral disease in Washington vineyards. The study used yield and fruit quality data obtained from previous WSU research that studied a commercial Merlot vineyard from 2009 through 2012. In that trial, yield was reduced from 12 percent to 28 percent during the four years. Further, Brix, which is a measure of sugar in the fruit, dropped below 23.5°, the desired contract minimum in seasons with below average growing degree-days (heat accumulation). Brix was measured at 23.1° and 22.5° in 2010 and 2011, respectively. There can be as much as a 2 percent price reduction penalty for each 0.1° Brix reduction below the 23.5° minimum. Yield and quality losses Data from the Merlot study were used to answer two questions: 1. How much is lost (in terms of operating returns) when fruit yield is reduced by 10 percent, 20 percent, or 30 percent? 2. How much is lost (in terms of operating returns) from a combination of reduced fruit yield and price penalty imposed by wineries when grapes have less than expected sugar levels? A base-line scenario for a Merlot vineyard was created using an average annual yield of 4.5 tons per acre and a three-year average price of $1,127 per ton. The associated variable costs were calculated using the Northwest Grape Costs of Production Calculator using 2014 prices and production practices for a vineyard in full production. Industry stakeholders participated in discussions and validation of costs estimated for grape production. Annual operating returns (excluding fixed costs) were calculated for a Merlot vineyard that had no virus infection as the base-line scenario. The base-line operating returns of $2,619 per acre were compared to the operating returns for vineyards managed under various virus infection scenarios of crop losses and reduction in fruit quality, especially sugars measured as Brix. (See Figure 1.) The study used two Brix Is 'Grape Virus Tax' hitting GOOD TO KNOW Annual losses from grape leafroll virus ESTIMATED IMPACT PER ACRE FROM REDUCED YIELD ONLY ESTIMATED IMPACT PER ACRE FROM REDUCED YIELD AND BRIX FIGURE 1 Net income $2,000 per acre $1,000 per acre Yield loss 0% –10% –20% –30% –$459 per acre –$918 per acre –$1,377 per acre Net income $2,000 per acre $1,000 per acre 0% –0° Yield loss and reduced °Brix –20% –0.4° –20% –1.0° –30% –0.4° –30% –1.0° –$1,243 per acre –$1,730 per acre –$1,661 per acre –$2,087 per acre SOURCE: AGRI-BUSINESS CONSULTANTS AND WSU Losses from grape leafroll virus over 20-year period LOSS OF OPERATING RETURNS PER ACRE FROM LOWER YIELDS AND FRUIT QUALITY FIGURE 2 –$4,000 per acre –$8,000 per acre –$12,000 per acre –$16,000 per acre –$20,000 per acre NPV* –10% –0.4° –10% –1.0° –20% –0.4° –20% –1.0° –30% –0.4° –30% –1.0° Yield loss and reduced °Brix *Net Present Value (NPV) was used to analyze JYXYVIGEWL¾S[W and account for the time factor. –$3,005 per acre –$8,272 per acre –$11,772 per acre –$16,443 per acre –$15,711 per acre –$19,799 per acre SOURCE: AGRI-BUSINESS CONSULTANTS AND WSU A new study estimates the economic losses from grape leafroll disease. by Naidu Rayapati and Doug Walsh, Washington State University COURTESY WASHINGTON STATE UNIVERSITY The Merlot vines on the right, with red leaves, are infected with grape leafroll disease. Notice the smaller clusters in the infected vine compared to a healthy vine on the left.