How well did winter bud injury measurements predict the final grape crop?
Tim Martinson, Hans Walter-Peterson, Luke Haggerty and Jim O’Connell
The arctic vortex last January brought repeated episodes of sub-zero temperatures to New York and other Midwestern and Northeastern states, raising fears of significant winter injury and crop reduction. Extreme low temperatures, ranging from -10 to -15° F in Lake Erie region, -6° to -22° in parts of the Finger Lakes, and -34° to -40° F in Northern NY, brought fears that significant bud and trunk injury would reduce the crop – not only of cold-tender vinifera grapes, but also hybrids and particularly the cold-hardy cultivars in Northern NY.
Cornell Cooperative Extension grape programs across the state were asked to evaluate the impact of winter injury on the grape crop – and particularly grapes available to Farm Winery licensees, who are required to source 100% of their grapes from New York.
The NYS Department of Agriculture and Markets (NYSDAM) is tasked with granting farm wineries waivers to the in-state purchase requirement if the crop of a particular variety is reduced by more than 40%. As early as March, NYSDAM was asking us to provide estimates of crop reduction so that they could determine which grape varieties qualified for the waiver for out-of-state purchase. With upwards of 30 vinifera, hybrid, and native cultivars used in winemaking in four distinct grape growing regions, this seemed like a daunting task.
In response, we surveyed over 200 vineyard blocks in the Finger Lakes, Lake Erie, and Hudson Valley to determine which grape varieties were likely to exceed the 40% crop reduction threshold. Midwinter collection of buds to determine the percentage of dead primary buds showed the potential for crop reduction was there. But it took a followup survey after fruit set to provide NYSDAM with estimates of which varieties exceeded the 40% threshold. Results were summarized in our publication Estimates of Wine Grape Crop Reduction due to Winter Injury in New York in 2014, and NYSDAM made the following determination in an August 18 press release, entitled Department of Agriculture and Markets Announces Actions to Assist Farm Wineries Affected by Harsh Winter Conditions:
"The combination of harsh winter temperatures, sustained cold, lack of snow cover, as well as alternating warmer and colder temperatures killed critical fruiting buds, vastly reducing 2014’s grape yield. Vineyards also saw trunk damage, which would necessitate the need for an entire plant to be replaced. Grape varieties covered under this declaration include: Riesling, Cabernet Franc, Pinot Noir, Chardonnay, Gewürztraminer, Merlot, Pinot Gris, Cabernet Sauvignon, Lemberger, Syrah, Gamay Noir, Brianna, Frontenac, La Crescent, and Noiret."
Bud Injury vs Midsummer Estimates. The midwinter bud examination survey and post-fruit set cluster number estimates provided us a unique data set to determine how well bud mortality estimates predicted cluster number and potential crop reduction.
1. Bud injury vs predicted crop. Over the 69 vineyard blocks with both surveys (Figure 1), midwinter bud injury accounted for 13% of the variation in predicted crop in the Finger Lakes and 30% of the variation in the Lake Erie region. While that shows that bud mortality predicted part of the potential crop, many blocks with primary bud mortality in the 60-90% range had a predicted crop in the 60-80% of ‘normal’ range – much higher than would be expected based on bud mortality alone.
Clearly, factors other than primary bud mortality influenced cropping levels in the surveyed blocks. The most important was undoubtedly changes growers made in pruning strategies: Growers experienced with winter injury left extra buds, which compensated for the observed bud mortality in their vineyard. It turned out to be a successful strategy.
2. Average by grape variety. When we plot the same data after averaging the bud mortality and crop across multiple sites (Figure 2), some of the variability we saw in Figure 1 drops out. Across 24 cultivars and two regions, primary bud injury now explains a higher amount of the variability (40%) than did the response line based on individual sites.
3. Trunk Injury across varieties and regions. We also rated the vines for trunk injury, rating them for 1) Full trunk renewal, 2) Partial Canopy, and 3) Full canopy. Figure 3 shows how trunk injury varied across cultivars. Note that most of the observed trunk injury occurred in the vinifera and Cold-Hardy ‘Minnesota and Swenson’ cultivars.
Practical implications. By the end of the season, it was clear that severe injury and crop loss was limited to specific ‘pockets’ of the Finger Lakes, Lake Erie and Hudson Valley regions – and serious vine injury was limited to V. vinifera cultivars.
In the Finger Lakes, the crop on more cold-sensitive cultivars (Merlot, Pinot noir, Gewurztraminer, Pinot gris, Syrah, Sauvignon blanc) was small. However more widely planted mainstays such as Riesling, Chardonnay, and Cabernet Franc, came through better than expected. Riesling outperformed many growers’ expectations – to the extent that some growers were selling their excess fruit on the NY Wine and Grape Classified site run by the Finger Lakes Grape Program.
Injury in the Lake Erie region reduced the crop on vinifera more uniformly – although damage was not as severe as has been reported further down Lake Erie in Ohio. Concord production was higher-than-average for the second year in a row.
Growers in the Thousand Island region, where temperatures dipped below -34 degrees F, did see significant injury and a reduced crop, as did others growing the cold-hardy ‘Minnesota’ varieties in the upper Midwest and Northeast.
Out of State sourcing. By the end of the season, Ag & Markets program coordinator Peter Pamkowski reported that the department approved five applications by NY Farm Winery licensees to purchase grapes out of state. These requests came from wineries in Orange, Tioga, Ulster, Washington, and Niagara counties. The varieties sourced were Cabernet sauvignon (2 requests), Cabernet franc (3 requests), Pinot noir, and Merlot.
Conclusions. Low temperatures last January and February caused significant bud injury in the Finger Lakes, Lake Erie, and Hudson Valley – leading to fears that production and vine injury would be heavily impacted, as it was in 2004. However, impacts were uneven – and growers compensated by leaving up to 10 times as many buds on the vines, and adjusting shoot number after bud burst. This strategy undoubtedly cost growers more money, but it also helped many produce close to a normal crop in the 2014 growing season.
Morrissey, J. 2014. Department of Agriculture and Markets Announces Actions to Assist Farm Wineries Affected by Harsh Winter Conditions. NYSDAM press release, August 18,2014. http://www.agriculture.ny.gov/AD/release.asp?ReleaseID=2922
Martinson, T. E., H. Walter-Peterson, L. Haggerty, J. O’Connell, and M. Colizzi. 2014. Estimates of Wine Grape Crop Reduction due to Winter Injury in New York in 2014.
Tim Martinson is senior extension associate with the section of horticulture, School of Integrative Plant Science, based at the NYS Agricultural Experiment Station in Geneva. Hans Walter-Peterson is extension educator with the Finger Lakes Grape Program in Penn Yan. Luke Haggerty is extension educator with the Lake Erie Regional Grape Program in Portland, NY. Jim O'Connell is extension educator with the Eastern New York Commercial Horticulture Team, based in Highland, NY.