Non-traditional Vineyard Canopy Management for Increased Crop Yield and Improved Fruit Quality

Final Report for FNC08-743

Project Type: Farmer/Rancher
Funds awarded in 2008: $6,000.00
Projected End Date: 12/31/2010
Region: North Central
State: Ohio
Project Coordinator:
Stephen Pearce
Ohio River Vista Vineyard, Winery & Research Station
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Project Information


The Ohio River Vista Vineyard and Research Station is located in Clermont County, Ohio. The 5.42 acre site overlooks the Ohio River in a southwesterly view 200 feet below and six-tenths of a mile distant. The unglaciated soil is rich in clay over limestone underlayment providing suitable drainage. To mitigate erosion, the vineyard rows are terraced east-west, perpendicular to the 30 percent, steeply-sloped ground. This ideal terroir is capable of supporting 3,000 vines producing as much as 1600 cases of fine wine per year. Vinifera varietals grown include cabernet sauvignon and cabernet franc. French hybrid varietals include traminette and vidal blanc. A field research facility hosts faculty and students of four nearby universities who are conducting collaborative projects. This new outbuilding houses processing and laboratory test equipment along with experimental seedling cultivars.

Beginning in 2006, we have strived to implement as many sustainable practices as possible for a vineyard planted on a steep slope. A water diverter positioned above the vineyard helps control hillside runoff. Native perennial ajuga is planted on the terrace banks to control erosion.

Weeds are allowed to grow along the terrace rows to disperse our more than ample seasonal rainfall and serve as a natural means of controlling vigor of the vines. Weed whackers are used to maintain this cover crop between two and ten inches high.

Because our vineyard has never used synthetic chemicals as pesticides, we are eligible for organic certification. We are fortunate to have sufficient beneficial insects for control of grape berry moths, cutworms and aphids. Fungus is dealt with as best we can using lime sulfur, copper hydroxide, Serenade and Regalia, all OMRI registered for organic cultivation. Careful positioning of vines in our vertical shoot positioned trellises along with sufficient leaf pull promotes air circulation for drying the canopy. Composting of vineyard cuttings along with lees (sediments), skins, and seeds from the winery is returned to the vineyard each year.

Goals: The purpose of this project was twofold:
(1) To replicate the results of a milestone study conducted at the University of California (Winkler, 1931) that has had significant and continuing impact on the growing of grapes by both large and small operations, and
(2) To demonstrate that a heretofore overlooked alternative interpretation of the results of the Winkler study, namely both increased crop yield (even doubling) and quality may be achieved at the expense of additional labor.

Winkler’s research has been quoted repeatedly in the decades following his work (Jackson 2000, Lakso 1999, Nuzzo 2006, Wagner 1996, et al.), and his recommendation to utilize the second best (in terms of crop yield and quality) canopy management system is universally followed. However, his study was directed toward large commercial growers whose labor costs were ever-increasing, and the small family farm situation was not addressed.

In overview, Winkler recommended moderate pruning of dormant vines along with appropriate thinning of flower clusters and immature grapes. Today this is referred to as ‘balanced pruning,’ and many different algorithms have been put forward to guide the vintner’s pruning efforts as prescribed by Winkler, the grape variety being cultivated, and the site’s historical production record. Yet to the contrary, Winkler’s results clearly show that the highest yields and best quality were obtained by cluster thinning (CT) only, and no pruning at all (NP+CT). Winkler states (see p. 296, Winkler et al., 1974) that when the crop is NP+CT managed:
“…vines produce twice as much as the normally pruned vines. The fruit also was of superior
quality – large clusters of uniformly large berries, with a high degree of Brix. In addition, these vines made the most growth of any of the vines with crop. Both vigor and capacity were high.”

‘No pruning’ and ‘cluster thinning only’ along with the phrases ‘twice as much crop’ and ‘superior quality fruit’ sounds too good to be true, but to the family farmer not overly concerned with increased labor it could prove to be a great boon. Clearly, if the cost of labor is not a limiting factor (i.e. on the family farm), the NP+CT technique of no pruning together with crop thinning is to be preferred.
1. Jackson, Ron S. 2000. Wine Science. Academic Press.
2. Lakso, Alan N. 1999. Physiology of Minimal versus Normal Pruning of Concord Grapes
3. Nuzzo, Vitale, Matthews, Mark A. 2006. Response of Fruit Growth and Ripening to Crop Level in Dry-Farmed Cabernet Sauvignon on Four Rootstocks. Am. J. Enol. Vitic. 57: 314 – 324
4. Wagner, Philip M. 1996. Wine Growers Guide. Wine Appreciation Guild; 3rd edition.
5. Winkler, A. J., Cook, J.A., Kliewer, W. M., Lider, L. A. 1974. General Viticulture. University of California Press; 2nd edition . (See pp. 287-300).
6. Winkler, A. J. 1931. Pruning and thinning experiments with grapes. California Agriculture
Experimental Station Bulletin, 519:1-56.

To replicate the UC Davis research, one-quarter acre of 3-year-old vines in alternating rows were managed according to the Winkler study using two contending techniques: No-Pruning-plus-Crop-Thinning (NP+CT) and Balanced-Pruning-plus-Crop-Thinning (BP+CT).

By way of further explanation, the expression “no pruning” does not mean to let the vines grow in wild disarray, rather this technique calls for careful positioning of vine shoots to avoid layering and entanglements of leaves and grapes. “No pruning” means that rather than trimming vines at the beginning of the growing season to reduce the bud count along with supporting foliage, all buds are allowed to leaf out. As a consequence, careful shoot positioning and removal of layered leaves that would otherwise overly shade is required. Clearly this NP+CT practice is highly labor intensive and not subject to automation.

Crop thinning without pruning requires the grower to make multiple passes through the vineyard starting at bud break and continuing throughout the growing season up to harvest. Flowers are removed wherever there is likely to be crowding of future fruit. As the season progresses, a balanced fruit load is achieved by removing clusters (up to 50 percent with some varietals). Crop thinning by this means also requires lots of manual labor.

Contrariwise, crop thinning by balanced pruning (BP+CT) trims dormant canes and spurs only once in late winter or early spring. This standard commercial practice may even be automated with certain trellis systems. Clearly this is the preferred technique for large production farms.

The significance of verifying the UC Davis study and re-interpreting the results with the small family farm as a focus cannot be overstated, namely both increased crop yield (even doubling) and quality may be achieved at the expense of additional labor. For the small family farm, greater crop yield obtained by greater labor is a reasonable tradeoff. Moreover, this farm, like other organic growers is very much interested in improving quality of produce as well as quantity. It is particularly important for organic fruit to present well in order to induce buyers to pay for the additional cost of organic production.

Spring 2009: Prior to bud break, seven rows of 3-year-old vines were traditionally canepruned, and the remaining fruiting canes were tied to fruiting wires. These vines served as the project control group. An additional set of seven rows (alternating with those of the control group) were purposely not pruned. Instead, the canes from the previous growing season were carefully positioned and tied to trellis supporting wires so that maximum separation of the canes was achieved. These seven rows served as the test group of vines.

At inflorescence, it was clear that the test vines had more flowers emerging than the control vines produced. This was a sure indication that fruit loading would be different. Also, it was noted that bud break began earlier for the non-pruned test vines. Flowering on control vines did not require thinning. Wherever crowding occurred on the test vines, flowers were pinched off
(as per Winkler).

Summer 2009: Both control and test vines were subjected to standard vineyard practice including support tying of new growth, north-side leaf-pull (to enhance air drying while limiting sun exposure), weed control (non-standard manual weed-whacking), and organic spraying (for fungus control). No insecticides were used, since each previous year demonstrated that enough beneficial insects were present to control their prey. Control group vines were topside hedged as usual (to limit vegetative growth). Contrariwise, test vines were allowed to fully propagate vegetation, although extra leaf-pulling and cane positioning was necessary to prevent the canopy from becoming too densely shaded. As expected, the test vines required considerably more labor to position the new growth shoots amongst the non-pruned canes of the previous season. Repeated passes through the test vine rows were required to ensure proper positioning of the excess growth to allow sunlight to penetrate the canopy.

As at inflorescence, thinning of clusters at berry set (to improve grape sugar content, flavonoids, and acidity) was not done to the control group because there appeared to be no excessive crowding. The test vines were minimally thinned wherever crowding was present.

Because the growing season was exceptionally wet, organic fungicide was liberally and equally (by volume) sprayed on the vines of each group to control black rot and bunch rot. As it turned out, by using the same limited spray regimen for both groups as determined by what the control vines needed was a mistake resulting in the test vine clusters experiencing undue bunch rot.

Fall 2009: Berries were tested for ripeness as harvest neared. Somewhat surprising was the finding that the test group fruit was lagging behind in sugar content (about one degree Brix) and acidity (albeit less than 0.2 % difference), although pH, tastes and appearance of similarly ripe grapes from each group were essentially the same. This appeared to present a serious problem with respect to harvest scheduling. For the study to be objective, it was felt that fruit from each of the groups should be harvested on the same day. Fortunately the weather cooperated and allowed the average sugar content to reach a minimum of 22 Brix, and although not all seeds examined had turned brown, it was decided to harvest before too much additional rain and cold weather arrived to possibly ruin the harvest.

Harvest 2009: Clearing weather with one day of sunshine allowed harvest to proceed under muddy conditions. Unfortunately the far from normal season, cool and wet, rotted the cabernet sauvignon fruit, so these 75 plants were not used in the study. The 75 cabernet franc vines were harvested, but a miscommunication resulted in the number of clusters per vine not being counted, only the clusters’ weight per vine. Fortunately, good data was obtained for the 30 traminette and 30 vidal blanc vines, both number and average weight of clusters per vine.

Spring 2010: As according to the previous season, dormant canes were pruned (control group) or positioned (test group) without pruning. As before it was noted that bud break began 4-6 days earlier for the non-pruned test vines. As expected at inflorescence, test vines had more flowers emerging than the control vines.

Summer 2010: Vineyard practice was followed according to that of the 2009 season. Because rainfall was less frequent than that of 2009, both groups of vines received the same organic treatment for fungus.

Fall 2010: Berries along the fruiting wires in both groups tested the same for ripeness as harvest neared. It was noted that berries of the test group that were distant from the fruiting wire were not as consistently ripe to the same degree as those on the fruiting wire.

Harvest 2010: Data was collected per 2009, both number and average weight of clusters per vine.

Two Ohio River Valley winegrowers volunteered their time contributing valuable suggestions, namely, Ron Barrett of Kinkead Ridge Vineyard and Bill Skvarla of Harmony Hill Vineyards. Dr. Mike Ellis of Ohio State University Extension was always willing to return phone calls and suggest reference materials.

• Canopy vigor of the test vines far exceeded that of the controls. Daily leaf pull became necessary following veraison. This practice not only kept the canopy open for air flow and sun penetration, but allowed for adequate spraying of organic fungicide.
• Fruit in the (non-pruned) test group started ripening about two weeks before the control group grapes, but whereas this process continued until harvest, the control group (balanced pruning) showed more even ripening.
• The average size and weight of individual grape clusters was statistically the same within one standard deviation.
• As expected, the test vine grape clusters outnumbered those of the controls. Although there was some overlap between the two sets of data, cluster counts were 1.4 times higher for the non-pruned test group.
• Weight of the combined clusters per vine was only 28 percent greater for the test group than that of the control vines. (40 percent more weight per vine would be expected based solely on cluster count).
• The appearance of the individual ripe berries was the same in both groups, but there was more bunch rot among the test clusters which appeared to be more crowded. This difference in cluster density may have resulted from the early shoot development and bud break of the test vines. It is likely that this could have been avoided if Winkler’s advice was more aggressively followed as far as thinning flowers at inflorescence (not fully explained in his reports). After crush, standard measurements of the juice showed no significant difference in pH, acidity, or degree Brix.
• The log of labor hours surprisingly showed only a 33 percent increase in hours spent on the test vines.

From these results it may be concluded that this two-year study only partially supports Winkler’s work. Standard pruning of the control vines resulted in less crop load, but the test vines only showed 28 percent more fruit weight albeit 40 percent greater cluster count. This result is not even close to Winkler’s report that “…vines produce twice as much as the normally pruned vines.“

Moreover, fruit quality was about the same for each group contrary to Winkler stating, “…fruit also was of superior quality.”

Conducting this study in the high-disease-pressure Ohio River Valley certainly introduces a variable that Winkler’s experiment did not have to deal with in California. Exacerbating this was the severely wet and cold growing season experienced during the first year of this study. It may be that the different climates could account for the different outcomes.

This project followed as closely as possible the procedure Winkler outlined in 1931 whereby he compared the harvest results of non-pruned vines with those of balance-pruned vines, and wherein he found that crop yields and quality were greater for the non-pruned group.
The results of this two year project only partially corroborated Winkler’s results. Instead of realizing a crop yield nearly twice that of the control group vines, this study showed a vine’s weight yield to be only 28 percent greater for the test group. Instead of harvesting fruit of superior quality as stated by Winkler, this study found the fruit from both groups to be comparable in terms of acidity and sugar content as well as taste.

Clearly the climate of California’s Central Valley is vastly different (drier, warmer, longer growing season) from the climate of the Ohio River Valley. This may account for the somewhat different outcomes of the two experiments.

Even though the two-times-crop yield results of Winkler cannot be substantiated for our North Central Region, it seems reasonable for the small family farmer to spend 33 percent more time tending vines in the non-pruned-plus-cluster-thinning manner to achieve 28 percent greater crop yield.

Drawbacks to adopting this practice include the greater difficulty in achieving adequate spray penetration to prevent fungal growth, and the unevenness of cluster ripening requiring additional harvest days.

Over the next several years, our plan is to continue this project by converting additional rows of vines to Winkler’s practice with the modification of limited pruning in place of no pruning. We will continue using vertical shoot positioning for our trellis system, but will advise growers of new vineyards who wish to follow the NP+CT technique to seriously consider doing so on a Geneva double curtain, lyre, or split canopy trellis system.

One scheduled field day was held mid-summer with only 14 growers attending, probably due to the poor weather. At least a half-dozen unscheduled field events were conducted once the word spread further.

The project overview was presented at our winegrowers’ annual gathering. Several farmers asked for additional information including the project website url.

Two growing seasons is limiting for some projects. Perhaps the Council would consider funding additional contiguous years for such projects showing promising results.


Participation Summary
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.