Freezes during early spring can damage flower buds of sweet cherry (Prunus avium L.). The reduction in sweet cherry production due to cold injury to floral tissue can be significant and is a common and serious problem for growers and commercial producers in the Pacific Northwest and other regions of the US. The critical temperatures affecting the bud and the associated damage are variable and unknown for most of the new cherry cultivars. The goal of this study was to identify the critical temperatures of cherries buds at different development stages, using differential thermal analysis (DTA) and a traditional cold exposure method for assessing cold damage. Three sweet cherry cultivars including Bing, Chelan and Sweetheart were tested during the late winter to early spring seasons of 2012 and late fall to early spring season of 2013. The DTA showed that the temperature causing freezing injury was related to the initiation of the low temperature exotherms (LTE’s), the value of the lethal temperature changes depending on the cultivar and bud development stage. High (HTE) and low temperature (LTE) exotherms were clearly identified for the different cherry cultivars that were evaluated during the early stages of bud development. Cold hardiness increased from late fall through mid-January, followed by deacclimation for the remainder of the winter months. During deacclimation, DTA was not an effective method for detecting LTE in cherry buds. Therefore, a traditional approach that exposes the tissue to different cold regimens was used for the remaining period of bud and flower development. To determine the total number of buds and flowers that were killed due to cold exposure, a simple evaluation using dissections under a stereoscope was conducted. Logistic models were developed for the freeze-survival data for both methods. Differences in hardiness were found for all the cherry cultivars that were evaluated as well as between different sampling dates. The information that was generated in this study will provide a better understanding of cherry cold hardiness and will support growers in decision-making of frost control practices.
