The proportion of organically produced crops in the United States has been steadily increasing. The 2016 certified organic survey conducted by the U.S. Department of Agriculture’s (USDA) National Agricultural Statistics Service (NASS) in conjunction with USDA’s Risk Management Agency showed that U.S. farms and ranches produced and sold $7.6 billion in certified organic commodities in 2016, up 23% from 2015. During the same year, the number of organic farms in the country increased by 11% to 14,217 and the area increased by 15% to 5.0 million certified acres. Similarly, organic grape (Vitis sp.) production has increased from 12,575 acres in 2000 to 27,358 acres in 2017 (USDA-NASS, 2017).
Interest in organic or biodynamic viticulture is also high in other wine-producing regions of the world as reported in Willer and Lernoud (2019), and as shown by the volume and diversity of research on the effect of nonconventional management practices on grape quality (e.g., Bunea et al., 2012; Núñez-Delicado et al., 2006; Reeve et al., 2005; Vian et al., 2006; Vrček et al., 2011). This interest is driven by increasing awareness of the negative effects that conventional agriculture has on the environment, and a willingness by a section of consumers to pay a premium for food with a smaller environmental footprint (D’Amico et al., 2016; Desta, 2008).
Wine grapes are an important specialty crop in the Commonwealth of Virginia. The Virginia Department of Agriculture and Consumer Services (VDACS) ranked grapes as the 10th most profitable commodity in Virginia with cash receipts of $19.1 million in 2017 as reported by the USDA (USDA-NASS, 2019). Virginia wineries and associated vineyards have increased appreciably over the past 10 years to ≈291 wineries (Conway, 2019) and more than 3300 acres of bearing vines (USDA-NASS, 2019). However, as of 2016, there was only one certified organic winery in the state of Virginia (Quality Certification Service, 2013).
In a 2008 survey conducted by the Virginia Wine Board, industry members identified sustainable production practices (78.9%), organic farming systems (47.7%), and cultivar and clonal selection and evaluation (71.1%) as priority areas for state viticulture research (Virginia Vineyards Association, 2008). These research areas are important for Virginia vineyards because of the need to capitalize on growing demand for organic wine and to avoid losing market share to wine regions that have adopted organic production methods. U.S. sales of organic wines reached $292 million in 2016, representing a 126% increase over a period of 10 years (Conway, 2018).
In the midwestern and northeastern United States, fungal and other weather-mediated grapevine diseases are typically the most difficult to control organically. Among them, powdery mildew (Uncinula necator), downy mildew (Plasmopara viticola), black rot (Guignardia bidwellii), phomopsis cane and leaf spot (Phomopsis viticola), and botrytis bunch rot (Botrytis cinerea) are some of the biggest challenges in wine grape production (Schilder et al., 2002).
In the current study, disease resistance and potential for organic production of four wine grape cultivars were tested under Virginia conditions. Compared with a majority of competing viticulture regions, Virginia’s humid growing season creates an environment conducive to the spread of fungal and other diseases. Black rot, downy mildew, powdery mildew, phomopsis cane and leaf spot, and botrytis bunch rot are common diseases that are especially difficult to control in the humid Virginia environment (Wolf, 2008). Any of these diseases can lead to total crop loss when environmental conditions are conducive, and organic copper, sulfur, and lime sulfur have historically been options for their control. However, these materials are not effective, particularly against black rot, and cannot guarantee vine survival or a healthy crop under typical Virginia conditions (Wolf, 2008).
Two of the cultivars chosen for this study: Arandell and Corot noir, represent new specialty wine grape cultivars developed by the Cornell-Geneva grapevine breeding and genetics program at Cornell University that thus far have limited representation in Virginia. These two red-fruited cultivars have been bred for disease resistance and quality wine characteristics. Trials with these cultivars conducted in New York State by Cornell University with minimal or no agrochemical input produced healthy vines with superior disease resistance and quality wine charac-teristics (Reisch et al., 2013). The other two cultivars, Petit Manseng and Vidal blanc, both white, were chosen based on their superior resistance against black rot compared with other traditional wine grapes. These cultivars are also known for high-quality wine and are already represented in Virginia viticulture.
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