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Grape Production and Management

Wine grape growing workshop helps grow the Virginia wine industry. 

Relevance: The Virginia wine industry adds 50 to 100 acres of new vineyard per year and currently comprises about 3,000 acres and more than 190 wineries. Wine grapes are a high-value horticulture crop requiring as much as $15,000 or more per acre in total establishment costs. Added to these costs is a large body of technical knowledge required by the beginning grower.

Grape Field

Vineyard site evaluation, choice of varieties, training system design, and pest management considerations must be generally understood upfront before embarking on vineyard establishment. Mistakes made in the preplant and vineyard establishment phases reduce the potential profitability of the vineyard and can delay the onset of commercial harvests. Prospective growers benefit from access to accurate and objective information on vineyard establishment.

Our response: An in-depth workshop for new and prospective grape growers was held at the Middleburg Agricultural Research and Extension Center in March 2011. Thirty-five potential grape growers attended this meeting, which was taught by Extension agents and specialists. Subject matter included market conditions, vineyard site evaluations, economics, variety selection, and basic vineyard design and operation.

Results: The workshop provided an orientation to the commercial grape-growing industry and introduced prospective growers to the concepts necessary for sustainable and high-quality grape production. In a follow-up questionnaire, attendees reported that they had greatly increased their knowledge and understanding of the basic requirements for vineyard establishment and operation. The workshop also provided an opportunity for Extension agents to learn and present components of the workshop and to increase their own awareness for future grape-growing questions.

Extension specialists and agents: Leslie Blischak, Tremain Hatch, Kenner Love, Mizuho Nita, Tim Ohlwiler, Alex White, and Tony Wolf.

Documentation of grape leafroll disease and determining management strategies

Relevance: Grape leafroll disease (GLD) is caused by several viruses called grapevine-leafroll-associated viruses. The typical visual symptoms in red-fruited varieties include a reddening of the interveinal area of the leaf blade while vein tissues remain bright green. In white-fruited varieties, visual symptoms include a slight chlorosis of the interveinal areas of the leaf blade. With heavy infection, both red and white varieties can exhibit symptoms that include leaves rolling downward, reduced vine vigor, reduced berry color and sugar content (Brix), and a potential overall reduction in crop yield of 30 to 50 percent total loss.

Because these viruses cause systemic infection, the only remedy to the situation is removal of infected vines; however, symptoms of GLD can be easily mistaken with various nutrient deficiencies, vascular diseases, and water stress. Therefore, it is important to determine the presence of viruses.

Transmission of these viruses can be accomplished through vegetative propagation, grafting, and insect vectors. These insect vectors (mealybugs and soft scales) seem to play a vital role in the spread of leafroll — especially mealybugs, because they are much more likely to move between vines. Thus, mealybug control should offer an effective means of minimizing the spread of grapevine-leafroll-associated viruses throughout a vineyard.

Our response: Although it was speculated that GLD is present among Virginia commercial vineyards, there was no information on the extent of infestation. We responded to this issue by developing a survey project involving molecular-based diagnostics of leafroll-associated viruses and analyses of spatial and temporal movement of the viruses. The collaboration between Mizuho Nita’s lab and Naidu Rayapati’s lab at Washington State University was established to provide services to each other.

In addition, we have been conducting a field experiment to determine the efficacy of insecticide applications against established mealybug populations. The Virginia Wine Board and also USDA’s Viticulture Consortium-East program have supported this research. A master’s level graduate student, Taylor Jones, joined the Nita lab for this project in fall 2010. In addition, a molecular-based diagnostic capability for detection of viruses was added to the Alson H. Smith AREC facility in spring 2011.

Results and expected outcomes: The survey effort collected more than 800 samples from 140 sampling sites. At this point (2009-2010), we have identified more than 50 percent of surveyed vineyards with some level of infestation by common leafroll-associated viruses (GLRaV-2 and -3). The preliminary data showed high correlation between the age of the vine and the presence of virus, probably due to a lack of clean plant materials prior to 1990.

At the same time, we found several newer vineyards with GLD, suggesting potential contamination at nurseries. We have been collecting data on the vector for this disease (mealybugs in particular), and we have identified grape mealybugs and the potential of a newly introduced mealybug species (it is suspected to be Gill’s mealybugs) in Virginia vineyards.

Field experiments with insecticide application showed:

  1. If new grapevines were planted adjacent to old, infected vines with mealybugs, transmission of the leafroll virus could happen within a few months.
  2. Regardless of insecticide application, mealybug population was sustained in the vineyard, suggesting the difficulty of controlling this insect.
  3. Seasonal changes of mealybug population seemed to be different each year; thus, environmental factors could be a key to determining its behavior.

In 2011, we added another field trial at a commercial vineyard to determine the efficacy of two newer systemic insecticides.

As of 2011, distributions of grape leafroll viruses in Virginia commercial vineyards have been documented, associations among different grape viruses have been examined, and management methods (insecticide application) have been examined in the field. We will continue this effort to gain a clear picture of the GLD situation in Virginia and to obtain more information on mealybug management.

Because of this research/Extension effort, growers are now aware of the extent of this important disease and the presence of mealybugs in their vineyards. In addition, the management options (obtaining “clean” grapevines, mealybug management, and rouging of infected vines) are communicated through various Extension channels, including Virginia vineyard association meetings, vineyard Extension meetings, and face-to-face meetings.

Because the principal investigator has done the sampling, this survey effort has also served as a face-to-face meeting opportunity for the investigator and growers. At these meetings, grape disease management issues in addition to GLD have been discussed. More than 50 meetings were held through this program in the 2009-2010 seasons.

Extension specialist: Mizuho Nita.

Extension and research efforts for effective grape fungal disease management

Relevance: Environmental conditions in Virginia are conducive for several fungal grape diseases that can cause significant economic damage. Growers may apply fungicides 10 or more times during the course of a season to manage diseases. While many of these spray applications are done properly, others may be unnecessary.

Grape Field

The misuse and overuse of fungicides not only raises economic issues (e.g., cost for chemicals, fuel, labor, etc.), but also environmental issues (e.g., fungicide resistance, fungicide drift, groundwater contamination, carbon dioxide output, etc.) and sociological issues (e.g., fungicide use in proximity to residential and/or public facilities, fungicide residues on crops). Thus, it is important to inform growers about effective uses of fungicides in order to reduce their misuse.

Our response: Both Extension and research approaches have been taken to address this important issue. Extension education has been made available through multiple avenues in collaboration with the Virginia grape industry. In addition to traditional site visits (more than 30 visits per year), phone consulting, and emails (more than 300 per year), grape disease management was discussed at vineyard meetings that were conducted six to eight times per year. More specialized integrated pest management (IPM) workshops were held one to two times per year.

Numerous grape-disease-related publications, such as the “VCE Pest Management Guide,” “Virginia Wine Grape Spray Guidelines,” and the “Southeast Regional Bunch Grape Integrated Pest Management Guide” were made available to the public. Several Web-based approaches, such as use of a blog and other social media (e.g., Virginia Tech’s Scholar site, Twitter, etc.), have been investigated and implemented.

In addition, we are developing a Web-based, disease risk-assessment system that has been supported by the Virginia Agricultural Council since 2010. We also conducted field trials where new fungicides were tested for efficacy against common grape diseases.

Results and expected outcomes: Dissemination of information to stakeholders has been one of the top priorities for addressing this issue. We have observed an increased awareness and application of IPM approaches, including diligent canopy management, increased interest in efficacy reports on newly introduced materials, and more interest in environmental, social, and economic sustainability among growers. Attentive growers are more aware of the biology of major grape pathogens, and they are seeking to manage diseases using both cultural and chemical options instead of relying solely on chemical management options.

Extension specialists and agents: Leslie Blischak, Tremain Hatch, Michael Lachance, Kenner Love, Mizuho Nita, Tim Ohlwiler and Tony Wolf .