Grape Growing in Pennsylvania In Spite of the Weather
By: Bryan Hed and Michela Centinari
The winter of 2014 will be remembered as one of the harshest for Pennsylvania grape growers. To begin with, the polar vortex that brought the ‘arctic’ to Pennsylvania in early January, caused severe damage to many wine grape varieties, especially cultivars of Vitis vinifera. During that event, temperatures in the Lake Erie region of Pennsylvania, fell from 47 F to below zero within 16 hours. Temperatures bottomed out at about -12 F (-24 C) and remained below zero (F) for about 20 hours. This was followed by steadily rising temperatures over the next several days, warming back up into the 50s. But the rollercoaster ride didn’t end there; there were several more severe cold events over the next 8 weeks as wave after wave of frigid air flowed through Pennsylvania vineyards. Our initial mission was to assess the damage to grape buds and compare the hardiness of the many grape varieties grown at two of our research farms: Rock Springs near the main Penn State campus (dead center of the state) and the Lake Erie Regional Grape Research and Extension Center in Erie county (northwestern corner of the state). Weather stations at both locations enabled us to track daily low temperatures through the period of the most intense cold (Figure 1 &2). As the ‘bad news’ came in regarding bud and vine cold damage, we began to rethink our plans for the 2014 growing season and see what we could learn from it. Our initial data are presented in the figures below.
Bud survival on different node positions among different dormant pruning strategies (Erie site).
As spring sprang, we began collecting data on Chardonnay and Riesling at the Erie site, examining shoot emergence at different node positions after the application of three different pruning strategies. Patterned after work conducted several years ago by Dr. Imed Dami on Pinot Gris in Ohio (Dami, 2012), we examined the effects of (i) no pruning, (ii) pruning to 5-6 bud spurs, and (iii) pruning to 2-3 bud spurs. Vines in our Chardonnay block had taken a major hit from severe cold over the winter and bud break was delayed with the loss of nearly all primary buds. Gradually, secondary and tertiary shoots appeared from a few node positions and percent bud survival (buds producing a shoot) among the different pruning treatments varied from 17% (average of first 10 nodes on non-pruned vines), to 21% (average of first 5 nodes on 5-6 bud spurs) to 26.5% (average of first 3 nodes on 3 bud spurs). Primary bud survival was thought to be less than 1%: of 2,600 nodes examined, only 5 produced shoots with two clusters (0.2%) and 11 produced shoots with one cluster (0.4%). Vines pruned to 2-3 bud spurs showed the highest percent bud survival among the most basal 3 nodes and shoot emergence at node position 2, was significantly higher on vines pruned to 2-3 bud spurs, when compared to ‘no pruning’ and ‘pruning to 5-6 bud spurs’. Among vines pruned to 2-3 bud spurs, shoot emergence at node position 1 (35 %) was significantly higher than shoot emergence at node position 3 (20%). Among non-pruned Chardonnay vines, there were no significant differences observed in bud survival among any of the first (most basal) 10 node positions.
Riesling vines appeared to suffer less severe winter cold damage than Chardonnay. Percent Riesling bud survival among the different pruning treatments varied from 24.3% (average of first 10 nodes on non-pruned vines), to 38.8% (average of first 5 nodes on 5-6 bud spurs) to 50.7% (average of first 3 nodes on 3 bud spurs). Of 1300 Riesling nodes examined, 6.5% produced shoots with one cluster, and 13.5% produced shoots with two or more clusters. So, about 20% of Riesling nodes examined were fruitful, whereas just 0.6% of Chardonnay nodes examined, were fruitful. Some trends in Riesling were similar to Chardonnay, where the highest percent bud survival (buds producing a shoot) among the most basal 3 nodes occurred among vines pruned to 2-3 bud spurs (44% (no pruning) and 47% (5-6 bud spurs) compared to 51% (2-3 bud spurs)). Among non-pruned Riesling vines, node 1 showed significantly higher survival (64% of nodes producing a shoot) than nodes 2 through 10 (which were not significantly different from each other).
Percent bud survival among different grape varieties at Rock Springs and Erie
As expected, there was tremendous variation in bud survival among the many grape varieties at the two research stations (Figure 3&4).
At Rock Springs in the center of the state, the most severe damage was observed in cultivars of Vitis vinifera, whereas French hybrids like Noiret, Corot Noir, La Crescent, Arandell, and Marquette showed fairly high levels of bud survival.
At the Lake Erie Regional Grape Research and Extension Center (Erie county; northwestern corner of the state), similar trends between V. vinifera and French hybrid/Native American varieties were observed. Old standards like ‘Vignoles’ and ‘Chancellor’ and the Minnesota hybrids were the winners, and appeared to fare as good as or better than even native varieties like Concord and Niagara. At both locations, Riesling, though seriously damaged, was generally the winner among the cultivars of V. vinifera.
Throughout the season, we will continue to evaluate the recovery of the different varieties and the effects of different pruning strategies in our Penn State research vineyards. Vine renewal will be a primary objective in many of our vineyard blocks. Sucker growth appearing at the base of our V. vinifera cultivars and our more heavily damaged hybrids, will be groomed as trunk replacements for 2015.
We are also beginning to see outbreaks of crown gall at the base of trunks where winter trunk damage has occurred on vines infected with the crown gall bacterium (Agrobacterium vitis). Some varieties, like Chancellor, are very susceptible to crown gall, and winter trunk damage may result in collapse of otherwise healthy looking vines with full canopies and full crops. So, don’t be too hasty to remove all sucker growth from otherwise healthy looking vines until you are reasonably sure the trunks are not developing crown gall. You should be able to observe new gall development on crown gall infected vines before the end of June (NOW). Areas developing galls will appear unnaturally swollen and the bark will appear to be splitting. New gall development can be detected if the bark is peeled from these swollen areas. The outside of new galls may initially appear dark on the surface, but the fresh white gall tissue beneath can be revealed with the scrape of a fingernail. If you find yourself renewing trunks on crown gall infected vines, always make sure to select scion-wood sucker growth emerging from below the gall affected area. Trunks with galls do not have to be removed this season, but can be retained for now to produce a potential crop and as a means of support for fastening suckers/new trunks. Diseased trunks can then be removed during winter dormant pruning, and replaced by the new trunks.