Progress report for OS17-107

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 [7]. 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 [8], 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.

Figure 2. Tunnel structure to cover the grape canopy, Okayama Prefecture, Japan

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 [9].) 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.

Figure 3.  Fruit bags on grape clusters. Winchester, VA Sept 2017

Figure 4. Fruit umbrellas on grape clusters, Winchester VA, September 2017

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 [12] 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.