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Carolyn DeMoranville and Irving Demoranville

Cold tolerance of cranberry flower buds from four cultivars was evaluated using potted sods collected from commercial cranberry beds. The plants were evaluated weekly beginning at the spring dormant stage and continuing until the buds had elongated to at least 2 cm. The potted plants were place in controlled temperature chambers at 5°C and the temperature was lowered 3°C/hr until the target temperature was reached. The plants were held at that temperature for 3 hr then slowly warmed. After 24 hr, damage was evaluated by microscopic examination of cross-sectioned buds. In the early spring, prior to leaf greening, all four cultivars were tolerant of –8°C. In the later part of the spring, cultivars with the smallest buds had greater cold tolerance than those with larger buds. Even when all cultivars appeared to be at the same developmental stage, e.g., bud swell, `Ben Lear' and `Stevens', were more sensitive than `Early Black' and `Howes'. At the 2-cm elongation stage, minimum cold tolerance of –1°C was reached for all four cultivars. New recommendations for protecting cranberry flower buds in the spring have been formulated based on this study.

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Carolyn DeMoranville, Irving DeMoranville, and Tom Bicki

Cold tolerance of cranberry (Vaccinium macrocarpon Ait.) flower buds (spring) and fruit had previously been investigated for the cultivars Early Black (EB) and Howes (H), leading to predictors of cold tolerance based on appearance of the buds (size and growth) and fruit (color). We studied these cultivars along with `Ben Lear' (BL) (buds only) and `Stevens' (S) using controlled temperatures to determine the accuracy of predicting cold damage. BL was the least cold-tolerant cultivar in early spring, both BL and S were less tolerant than EB and H during budbreak (-2.8C vs. -3.9C) and elongation (-2.8C vs. -1.4C), and all survived any exposure to -1.4C. EB fruit were tolerant of -5C once maximum color was achieved and 2 weeks later would tolerate short exposures to -6.5C or less. H fruit developed deep tolerance (below 6.5C) by November in only 1 year out of 2. S fruit were least tolerant: -5C for short periods at M maturity. The phenological model used to predict cold tolerance of flower buds was 48% accurate in our trials, generally overestimating bud tolerance, particularly for BL and S. EB fruit showed more tolerance than predicted, H less.