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Cold Hardiness and Temperature Responses of Healthy and Mildew-Infected Terminal Buds of Apple During Dormancy. R. A. Spotts, Mid-Columbia Experiment Station, Oregon State University, Hood River 97031; P. M. Chen, Mid-Columbia Experiment Station, Oregon State University, Hood River 97031. Phytopathology 74:542-544. Accepted for publication 2 January 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-542.

Cold hardiness of healthy and mildew-infected terminal buds of apple trees (Malus domestica ' Newtown' ) was determined monthly during the dormant period between 1 December 1981 and 1 March 1982. The lowest survival temperature (LST) of each bud was evaluated by the combination of visual observation, forcing, and grafting methods. The results obtained by using the three methods for the evaluation of LST agreed to within ± 2.9 C. The hardiness level of healthy buds was between - 25.7 and - 26.7 C during December to February and decreased to - 18.9 C in March. The hardiness level of mildew-infected buds fluctuated between - 16.4 and - 21.6 C during the entire dormant period. Incubation of terminal buds for 1 wk at - 12.2, - 1.1, +10 C, and ambient (+3.3 and +7.7 C) temperature prior to freezing resulted in different survival patterns in January and February 1983.

Additional keywords: freezing injury, freezing survival, Podosphaera leucotricha.