Low-temperature survival of blackberry cultivars grown in the midwestern United States

Commonly grown blackberry cultivars are susceptible to low-temperature injury throughout their dormant period. A study was conducted to evaluate the temperature at which 50% of the flower buds of nine blackberry cultivars were killed (T₅₀) following exposure to low temperatures. Blackberry cultivars evaluated included ‘Apache’, ‘Arapaho’, ‘Caddo’, ‘Osage’, ‘Ouachita’, ‘Navaho’, ‘Natchez’, ‘Ponca’, and ‘Von’. Tissue for artificial freezing tests was collected from a research planting near New Franklin, Missouri, USA on January 17, February 28, and November 21, 2022 and January 11, 2023. Immediately after each collection, canes were prepared for low-temperature exposure at a cooling rate of 3°C h^‑1. Primary flower bud hardiness among all cultivars varied by 7.2, 13.6, and 6.8°C in January, February, and November 2022, respectively. Due to a naturally occurring low-temperature event in December 2022 (-22°C), primary flower bud survival was evaluated on January 11 and February 28 in 2023. At all test dates, ‘Ouachita’ primary buds had consistently low T₅₀ values and high percent survival. In contrast, ‘Natchez’ primary buds had the highest T₅₀ values and low percent survival among the cultivars. Secondary buds of ‘Natchez’ had 34% survival on both dates in 2023. Based on the results of this study, ‘Ouachita’ flower buds had superior cold tolerance among the cultivars tested in mid-winter and just before budbreak in late winter.