Non-traditional Vineyard Canopy Management for Increased Crop Yield and Improved Fruit Quality
As planned, grant funds were used solely for labor by experienced vineyard workers assisted by student help.
Spring 2009: Prior to bud break, seven rows of 3-year-old vines were traditionally cane-pruned, 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 (for sun exposure), weed control (non-standard manual hoeing), 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 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: 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.
• Canopy vigor of the test vines far exceeded that of the controls. Growth of vegetation was so great for the traminette and vidal that 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.
• Control fruit started ripening about two weeks before the test grapes, but whereas this process continued until harvest, the test group showed more even ripening. The early start of the controls may have been due to stress induced by insufficient vegetation to support the crop load. The more even ripening of the test clusters may have resulted from their having sufficient vegetation, or because of weather change over the two week lag period, or because the test vines had more mature canes to start with.
• 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 the controls, although there was some overlap between the two sets of data.
• Average weight of the combined clusters per vine was 22% greater for the test group than that of the control vines.
• 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. Clearly the test fruit caught up with the ripeness of the control berries.
Given these first season results, it is tempting to conclude that the study only partially supports Winkler’s work. Standard pruning of the control vines resulted in less crop load, but the test vines only showed 22% more fruit, not even close to his report that “…vines produce twice as much as the normally pruned vines.“ Fruit quality was about the same for each group contrary to Winkler stating, “…fruit also was of superior quality.” Moreover the extra rot found on the test clusters arguably lessens suitability of those grapes for winemaking.
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 this year. Several local growers lost some crop to rot. One grower in frustration stated, “Thankfully this is a one in twenty-five year event.”
The one certain conclusion that may be drawn at this time is that at least another growing season will be required to compare with Winkler’s results.
WORK PLAN FOR 2010
For next season’s work plan to most closely repeat this year’s study, the alternating rows of test and control vines will be interchanged so that the non-pruned vines of this year will be traditionally pruned next spring, while the pruned vines from this year will become the non-pruned control group.
Next year the same protocol will be followed with one exception: if the season again proves to be too wet and cold, then the test vines will be more aggressively sprayed with organic fungicide to prevent rot.
Field days will be conducted next growing season which will surely be less wet and cold! This year only my two winegrower advisors were regularly apprised of progress. One site visit was made.
No results were available for the workshop presentation at Harmony Hills Vineyards as planned. A description of the project underway and some early indications of progress were communicated to interested attendees.
A project website will be completed to post the proposal, data, and conclusions, together with photographs.
The remainder of planned outreach will also be done next season with one sad exception: our student is destined for deployment overseas.