The recent economic impact study on the VA wine industry showed an annual contribution of $1.3 billion dollars to the state’s economy. The total acreage of certified organic grape production has increased from 12,575 acres in 1995 to 38,664 acres in 2011. However, only three Virginia vineyards have been approved by the USDA for their organic management practices for wine grape production, and only one has a winery. The main reason why organic wine grape production is not common in VA or any other states located the east of Rockies is fungal diseases, which are driven by frequent rain events during summer months. Thus, the Nita lab has established two experimental vineyards with financial aid from the USDA/NIFA VDACS Specialty Crop Research Initiative Block Grant in 2012. Although we identified several cultivars that may do well with the organic practice, there are two big challenges: a disease called black rot, which none of the OMRI-certified chemicals works sufficiently, and a potential loss of copper fungicides due to a trend of tighter regulations in other countries. Rather than searching for other chemical components, which is usually in the hands of chemical companies, what we proposed is the use of paper bags or umbrella to individually protect grape clusters. These bags and umbrellas are made out of water resistant paper, designed to fit grape cluster, easily applicable with an embedded wire, with small holes for ventilation and water drain, and expected to last for a whole season. (Note: light exposure to the cluster is not required for berry maturity.) The bagging practice most likely reduces the number of fungicide and insecticide applications because once bagged, clusters are protected from water and insects. Although application will be very labor intensive, a conversation with our farmer cooperator (and the only certified organic winery owner and grower in VA), Mr. Hambsch, revealed an extremely high cost of intensive removal of disease berries that is necessary for his production. Thus, even without the bag, they are already spending a lot of time and resources to the point that it will affect their profitability.
We will set up two vineyard trials to: 1) Determine the efficacy of paper bags and umbrellas against development of multiple fungal diseases on wine grape cluster grown with organic practices; 2) Determine the timing of bagging/umbrella application for the optimal disease control; 3) Examine the efficacy of fungicide-pre-coated paper bags; and 4) Examine economic benefits and hurdles of using individual cluster protection method. The information obtained from this study will be shared with our stakeholders through Extension meetings and other media outlets.
Basic idea here is to provide a physical barrier to prevent wetting of clusters, which is the condition for many fungal disease developments. In some countries, grapes are grown under a cover (Fig. 2), but with a high cost. Assuming it is similar to building a simple frame high tunnel, it will be approximately $1.50-$2.50 per square foot . Even if we cover only 1/3 of the area where grape canopy occupies, the cost will be $27,780 – $36,360 per acre (acre = 43,560 sq ft). An acre of wine grape yield 3-5 tons of fruit, and a ton of fruit ranges from $1,000-$3,500 , thus, each year, the revenue will be $3,000 to $17,500 per acre, but the price of high yielding cultivars is more likely to be at a lower end of the price range, thus, a revenue of $17,500 is very unrealistic. Unless you have highly productive vine that can be sold in high price, another capital investment may not be feasible. Plus, we lack information on how these over-the-trellis umbrellas can actually reduce wetting of clusters, or the adverse effects due to the lack of light penetration to the canopy.
Therefore, our proposed approach is the use of paper bags (Fig. 3) or umbrella (Fig. 4) to individually protect grape clusters. These bags and umbrellas are made out of water resistant paper, designed to fit grape cluster, easily applicable with an embedded wire, with small holes for ventilation and water drain, and expected to last for a whole season (Hosino Inc., Niigata, Japan). (Note: light exposure to the cluster is not required for berry maturity .) The bagging practice most likely reduce the number of fungicide and insecticide applications because once bagged, clusters are protected from water and insects. Although application will be very labor intensive, a conversation with our farmer cooperator (and the only certified organic winery owner and grower in VA), Mr. Hambsch, revealed that he sends out his crew of two only to remove diseased leaves and clusters during the critical times of black rot infection, which is three- to four-week period after bloom. This accounts for $1,664 per acre per season (2 people x 8 hr per day x 2 day x 4 pass x $13 per hour wage). Thus, even without the bag, they are already spending a lot of time and resources to the point that it will affect their profitability. With this intensity of disease management, bagging of cluster will not only reduce the labor cost, but also reduce soil compactions and CO2 emissions that are associated with traffics in the vineyards. Typically, cost of a bag is around 1-3 cents, and our current estimate of the cost for time to apply bags is about 2 cents per cluster. I.e., with 3-5 cents per cluster, we can produce wine grape organically while reducing pesticide usages.
Approach and Methods
Our objectives are: 1) Determine the efficacy of paper bags and umbrellas against development of multiple fungal diseases on wine grape cluster grown with organic practices; 2) Determine the timing of bagging/umbrella application for the optimal disease control; 3) Examine the efficacy of fungicide-pre-coated paper bags; and 4) Examine economic benefits and hurdles of using individual cluster protection method.
Field experiments will be conducted at two locations 1) Organic experimental vineyard at AHS Jr. AREC, Virginia Tech, Winchester, VA (hereafter referred as AHS AREC vineyard), and 2) Loving cup vineyards, North Garden, VA.
At AHS AREC vineyard, a section of organic experimental vineyard which consists of four cultivars (‘Arandell’, ‘Corot Noir’, ‘Petit Manseng’, and ‘Vidal blanc’) will be used. These vines were planted in 2012, and trained in cane-pruned vertical shoot positioning system (VSP). Vine spacing within a row is 4 ft and between rows is 9 ft. The vineyard consists of four rows, and each rows contains four replications of each cultivar, which are planted in triplicate (i.e., three consecutive vine of the same cultivar). In between each replication (or block within a row), there is three vines of Arandell to provide a buffer space. The experimental design will be a split-plot design where each row will be considered as a main plot, and a set of cultivar will be considered as a sub-plot. The main plot factors are: 1) Copper + bag; 2) Copper + umbrella; 3) Copper alternatives + bag; 4) Reduced input conventional fungicides + bag. At sub-plot level, there will be five treatments: 1) No cover; 2) Cover at bloom; 3) Cover at pea-size; 4) Cover at bunch closure; and 5) Cover at veraison. Each treatment will be assigned randomly within each cultivar. Three clusters per vine (= nine clusters per sub-plot) will receive each treatment, thus, a total of 36 clusters will receive the same combination of the main and sub-plot treatment. Copper (Cueva, Certis USA) applications will be made with 14-day interval, with an exception of one additional application at bloom. This typically resulted in 12 applications per year. Copper alternative will be Serenade Optimum (Bayer) or other biological agents and compost tea (or components of compost tea, which can to be used as alternatives) applied with the same timing as copper applications. Reduced input conventional treatment is a combination of protective [Stylet Oil (JMS Stylet Oil), Quintec (Dow), Revus (Syngenta), Cueva] and systemic materials [Luna Experience (Bayer), Vivando (BASF), Abound (Syngenta), and Prophyt (Helena)], applied eight times a season.
At Loving Cup vineyards, four rows of a cultivar ‘Corot Noir’ will be used for the experiments. The experimental design will be a randomized complete block design. Each row of 60 vines will be considered as a block, and within a block, there will be four subplots of 15 consecutive vines that will receive treatments: 1) No cover; 2) Cover at pea-size; 3) Cover at bunch closure; and 4) Cover at veraison, which will be assigned randomly to subplots. This larger scale experiment will allow us to record the time required for application to determine the true cost of application. I.e., how long does it take to apply these bags in a filed setting. Twenty clusters per sub-plot will be randomly sampled (= 80 total clusters per treatment) for the assessment at harvest.
The second experiment is to examine the efficacy of fungicide-coated bags. Since Loving Cup is certified organic, this experiment will be conducted only at the AHS AREC. The second vineyard at the AHS AREC consists of cultivars ‘Cabernet Franc’, ‘Chambourcin’, ‘Chelois’, and ‘Vignoles’. This vineyard has two rows, and the two main plot factors will be 1) Copper and 2) Reduced input conventional fungicides, and at the sub-plot level, there will be five treatments: 1) No cover; 2) Bag cover at pea-size; 3) Fungicide-coated bag cover at pea-size; 4) Bag cover at berry touch; 3) Fungicide-coated bag cover at berry touch. As with the other AHS AREC vineyard, nine clusters per sub-plot will receive each treatment randomly; thus, a total of 36 clusters will receive the same main and sub-plot treatment combination.
All proposed experiments will be conducted in two seasons to validate repeatability of the treatments. Assessments will be made at the time of harvest, and we will measure disease incidence (yes/no) and severity (% area infected), insect/animal damage (feeding, etc), average cluster weight and size, and average berry size and weight based on 100 random samples. Diseases to be examined are: black rot, Botrytis gray mold, downy mildew, powdery mildew, Phomopsis fruit rot, ripe rot, sour rot, and other rots that we may encounter. Additionally, pool of 100 random berries will be send out to VT’s enology lab for juice quality. Brix (% soluble sugar), pH, Malic acid, titratable acidity, Yeast Assimilable Nitrogen, and color profile (Anthocyanin) will be measured. In order to minimize cost, we will only submit samples from “copper + bag” and “conventional + bag” main plots, cultivar Corot Noir, of the AHS AREC experiment, and one sample per treatment from Loving Cup vineyard experiment. Also, a small temperature/relative humidity sensor with a data logger  will be placed in one of bags to monitor changes in temperature and relative humidity in the bag.
Disease, feeding, cluster, berry, and environmental data will be analyzed using a generalized linear mixed model (PROC GLIMMIX, SAS, ver. 9.4, SAS Institute, Cary, NC) to determine the effect of treatments.
At both AHS AREC and Loving cup locations, black rot was the major disease that developed in the 2017 season. At Loving cup location, we found both the proportion and disease severity of clusters with black rot were found to be significantly affected (P < 0.05) by the bagging practice, and the degree of the reduction of black rot also depended on the timing of bag application.
In short, we found significantly lower the proportion of grape cluster with black rot when we applied the bag at pea-sized berry, and the proportion increased as the timing of bagging moves away from the fruit set (i.e., bagged later).
The trend was very similar when we examined the disease severity (% of area diseased).
We found the significant effect of bagging to the severity of black rot on grape cluster. Although it was numerically lower, application at pea-size and berry touch did not significantly differ (P > 0.05) from each other.
We also examined the temperature in the fruit bag.
As we expected, the temperature inside of a fruit bag tended to be higher when the ambient temperature was high and the temperature also depended on where the cluster was located. For example, at the ambient temperature 90F, the temperature inside of the bag at shaded cluster was 97F and at sun-exposed cluster was 100F. On the other hand, when the ambient temperature was low, the temperature inside of the bag tended to be lower. For instance, when the ambient temperature was 50F, the temperature inside of the bag was in lower 40F. We think this refect the temperature during the night. The air inside of the bag was probably cooled down during the night, and took a longer time to be warm up when the sun comes up. We did not see any noticeable difference between bagged and unbagged clusters in terms heat-related damages (burning of berries, etc.).
We are still examining the data from AHS AREC where we had more factors to be tested. A preliminary result showed that umbrella was not very effective means of protection, and the fungicide amended bag did not add any more benefit to black rot control. As with other field experiments, we need to repeat at least in two years to confirm that the practice will be repeatable. However, we are encouraged by the positive outcome of the 2017 trials, and looking forward to the 2018 season.
In 2018, we are also planning to have a field day to discuss pros and cons on bagging exercise. We do not see the bagging practice to be applicable to all grape growers in VA, but it will be a good tool for organic growers as well as small-scale growers who may not have time to apply pesticide weekly. This practice may also be applicable to commercial growers who produce premium quality wines.
One potential drawback of the bagging is the reduction of color with red-fruited cultivars. We noticed noticeable changes in the color at both locations. It will be beyond the scope of the proposed research, but it would be worth investigating to determine the reduction actually affect wine quality.
Educational & Outreach Activities
An oral presentation was given at the 93rd Cumberland-Shenandoah Fruit Workers Conference, which was held in Winchester, VA in 31 Nov. to 1 Dec. in 2017. The target audience is University researchers, consultants, and chemical company representatives. An abstract was submitted for the proceedings.
We are currently preparing an industry newsletter article which will be published on April 2018.
Importance of protection of grape clusters against pathogens
The three pillars of the sustainable agriculture are: environment; economy; and social (common ones used in different disciplines) and/or profit, stewardship, and quality of life (proposed by SARE) . VDACS ranks grapes as the 18th most profitable commodity in Virginia in 2014 , a total of $740 million annual economic impacts by the VA wine industry was reported in 2011 , and more than 250 wineries exist throughout the commonwealth in 2016. Although the upward trend may continue for a while, we need to think ahead and come up with strategies to help the sustainability of vineyard operations and winery businesses, which are the backbone of our industry. The increased profitability with organic production can be achieved by potentially higher price tags accepted by target consumers, and/or by avoiding potential loss of market share by apt to the increased demands for organic certified options .
The practice we proposed here will reduce unnecessary environmental outputs while increasing profit margins by reducing the use of insecticides and fungicides, which covers both profit and environmental stewardship. It touches the quality of life because people living within proximity of vineyards will benefit from reduced fungicide drifts. Additional profitability potentially achieved by the covers are: bird and animal protection (no need for bird netting or squirrel and raccoon hunting), less need for leaf pulling (very common and time consuming practice), potentially no needs for deer fencing (another expensive capital investment and aesthetically not pleasing), and increase in yield and quality (Fig. 4). The proposed practice, which uses a compostable paper material to reduce pesticide usage, probably face less oppositions from citizen and government entities than traditionally farmed operations, thus, it will help the improvement of neighbor and community relations . The use of environmentally sound practice most likely can be used as a marketing tool to attract more customers to the winery. “Handcrafted wines from individually bagged clusters for low pesticide usage” should appeal to wide range of customer groups.
Thus, with the proposed project, each pillar interacts to each other, which is how the sustainability develops. This study will generate new integrated pest management tools for sustainable viticulture in Virginia that will further help the industry expand and provide more revenue for vineyard owners and the state of Virginia. We do not envision every cluster in VA vineyards to be covered, but growers most likely to implement this for high-value cultivars that can earn a premium price. Lastly, we proposed to utilize the covers in organic wine grape production because this approach seems to fit better with organic practices; however, it can be adapted to conventional grape growing methods. In fact, with the availability of systemic fungicides and insecticides, it may appeal better to conventional growers who want to drastically reduce the use of fungicides and insecticides. Due to its simplicity, the cover can be used on vineyards in other states in the South (which is also increasing in numbers) as well. To our knowledge, there are no other grants that overlap with the proposed research.
It would be nice to have a longer timescale for the project. Especially when we want to measure the sustainability of a practice using in-field experiments, 2 years is too short.