Grape cultivars differ greatly in their ability to withstand cold winter temperatures and the selection of hardy cultivars for cold sites is important. V.vinifera cultivars are much more sensitive than American cultivars and there are published list of grape winter hardiness (e.g. Clore et al. 1974). Extreme winter minimum temperatures are probably the most important site criteria for New York vineyards. The recommendations of Jordan et al. (1980) are that acceptable sites should have less than two occurrences of -15o F (-26oC) per ten years, whilst good sites stay above this temperature. Shaulis and Detheir (1970) suggest that sites with occurrences of -5oF (-20.5oC) more than once per year are likely to be at risk of cold injury. Martin (1971) suggest -7.6oF (-22oC) as a reasonable cold limit for growing V. vinifera grapes. Tukey and Clore (1972) suggest that there will be little winter injury at -1oF (-18oC) but that -9oF (-23oC) will kill most V. vinifera varieties. Meiering et al. (1980) found that extensive mechanical damage to phloem and xylem layers occurred at -13oF (-25oC). Prescott (1965) quotes French observers who describe 5 to -0.5oF (-15 to -18oC) as 'the ultimate limit of danger in winter'. Winter winds may also serve to reduce the heat budget for a site and thus increase cold injury (Dry and Smart 1988).
The warmest regions in the County are the Western shores of Lake Cayuga which have extreme temperatures of -23 F. The eastern shore of Seneca lake is only a degree colder. The elevated areas in the southern end of the county are upto 3 degrees colder. The remainder of the county in the north has temperatures of 24 F. Caution should be given in interpretation of these results since individual sites may be substantially warmer or colder than this because of either local topographic or lake influences.
Methodology for construction of climatic maps
Frost free days
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