Modeling Grapevine Cold Hardiness as a Predictive, Site- and Cultivar-Specific Online Decision-Aid Tool for Vineyard Freeze Protection
Cold injury due to low winter temperatures remains an important environmental challenge in many grape-growing regions throughout the United States, but especially in the northern states. Grapevines are adapted to the recurring seasonal changes in temperature by being able to develop a certain tolerance of low temperatures that is termed cold hardiness. Cold hardiness follows a somewhat predictable seasonal pattern: an acclimation phase (gain of hardiness) in late fall precedes a period of maximum hardiness in midwinter which is followed by deacclimation (loss of hardiness) towards spring, as the vines prepare for budbreak. Yet fluctuations in temperature lead to ?noise? in this general trend, because lower temperatures are associated with acclimation, while higher temperatures are associated with deacclimation. During the first year of this three-year project we developed a prototype computer model of the changes in cold hardiness of grapevine buds during winter. This initial model uses time steps of one day along with the measured daily mean air temperature to calculate the daily change in bud hardiness, which is then added to the hardiness from the previous day. The model simulates natural changes by estimating daily increases or decreases in hardiness depending on temperature. It also integrates a genetic component by altering the mathematical equations for different grape cultivars. We started by applying our model to Chardonnay, Cabernet Sauvignon, and Concord; these three genetically distinct cultivars demonstrate the variation in cold hardiness dynamics that our model?s flexibility is able to explain. In its current version the model is able to explain 89%of the variation in bud hardiness for Cabernet Sauvignon and Chardonnay, and 82%of the variation for Concord. More cultivars, as well as different vineyard sites, will be added during the remainder of this project. We are currently integrating the model into Washington State University?s AgWeatherNet (http://weather.wsu.edu), a network of 132 weather monitoring stations distributed across the state of Washington, to allow prediction of grapevine cold hardiness throughout the state. This innovative tool, along with weather forecasts and cell phone applications, will aid in the anticipation of and response to potential damage from fluctuations in winter temperature and from extreme cold events. This will allow growers to plan the implementation of cold protection measures, adjust pruning practices, and, in the long term, facilitate site selection for new vineyard developments.