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Abstract
Freezing temperatures on 7 April 2009 damaged developing pecan [Carya illinoinensis (Wangenh.) C. Koch.] buds throughout most of Oklahoma. Bud injury was evaluated on several cultivars at an orchard in northeastern Oklahoma. Bud death varied among cultivars with the greatest rate of death in 'Pawnee', 'OK642', and 'Mohawk'. The cultivars with the best bud survival were 'Giles', 'Kanza' and 'Mount'. Within cultivars bud survival was closely related to the bud development stage. However, comparisons at the same bud development stage indicated that certain cultivars possessed greater cold tolerance. Thus cultivars avoiding damage had a later budbreak and/or developing tissue had greater freeze tolerance. Budbreak was delayed on branches that were vegetative the previous season compared to those that bore fruit, resulting in less bud injury on vegetative branches in some cultivars.
Several reports have documented pecan tree damage from fall (4, 7, 14, 16, 22, 24, 25) and winter injurious cold temperatures (3, 13, 18, 29). Tree stress caused by previous season crop load (17, 19, 22, 31) or nutrient shortage (14, 17, 24, 29) predisposes trees to cold injury, and when combined with premature defoliation trees may be damaged when exposed to relatively mild winter temperatures (31). Susceptibility to injury caused by cold fall or winter temperatures differs dramatically among pecan cultivars (3, 4, 15, 16, 19, 21, 26, 29). The ability to withstand exposure to cold temperatures is a heritable trait that closely relates to the tree's origin, although there are notable exceptions that allow selection of cold hardy genotypes from southern locations (30).
Fewer reports document the effects of spring freezes on injury to pecan (5, 8, 9, 20, 27). Pistillate flowers of pecan are born terminally on current season's shoots that arise from a terminal mixed bud or lateral compound buds on 1-yr-old branches. Male flowers are produced from compound buds on 1-yr-old branches. Terminal mixed buds are found on shoots that were vegetative the previous growing season (6). The mixed bud frequently aborts leaving a lateral compound bud as the most distal bud. Branches that bore fruit the previous season typically retain the fruit rachis at the terminal end with a lateral compound bud as the most distal bud. The number of buds at a node varies...