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Friday, February 6, 2015

Grapevine Cold Hardiness

With all of the snow and cold that has been hitting our region of Connecticut this February, I'm looking back at my blog posts regarding grapevine cold hardiness and found two posts.
November 2011: Cold Tolerance and Grapevine Phenology
February 2014: Cold Hardiness of Grapevines Through Cold Acclimation

There are always new resources coming on line and I found one called Grapevine Cold Hardiness: Real-Time Cold Hardiness Monitoring from Washington State University where critical temperatures for wine and juice grapes are determined using a method called “differential thermal analysis”. Differential thermal analysis (DTA) measures the extent of cane phloem and xylem injury, based on tissue browning. DTA is not only used to conduct research on the mechanisms of freeze tolerance, but also to predict the critical (lethal) temperatures for grapevines. This research is detailed in a paper written by L. J. Mills, et. al. in the American Journal of Enology and Viticulture.1 There is a very helpful photograph in this paper of what bud and cane winter injury looks like:
In addition, there is a YouTube Video that walks you through the details of the data collection as well as the development of the Cold Hardiness Model:
Learn how to use the Grape Cold Hardiness Model on Washington State University's AgWeatherNet
This is an example of a graph of the Cold Hardiness Model.
The graph is similar to the "lethal temperature 50" or the LT50 graph, but it is also specific for grape variety and is predictive, based on the temperatures recorded. The Washington Cold Hardiness Model will show when freeze events could have led to Bud-10, Bud-50 and Bud-90 kills. As with the LT50 graph, the most susceptible time for bud mortality is during the fall acclimation phase and the spring deacclimation phase when buds have been exposed to a sudden drop in temperature after the arrival of warm temperatures.
The Washington Cold Hardiness Model is not applicable to Connecticut, but it is interesting to note the response of dormant vines to weather fluctuations. Also, the data collection was done on vines that were 20 years old so they have probably acclimated to their specific growing conditions in Washington State.
We need something like that for Connecticut!
References:
1. Lynn J. Mills, John C. Ferguson, and Markus Keller, Cold-Hardiness Evaluation of Grapevine Buds and Cane Tissues, Am. J. Enol. Vitic., 57:2 (2006).

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