2017 ASHS Annual Conference

Long held records for (low) chill hour accumulation have recently been broken several times in the southeastern US peach (Prunus persica) production areas. Long term historical average chill hour accumulation through February 15^th in middle Georgia has dropped significantly over the last 15 years. Trends in chill hour accumulation will be discussed along with its import for both commercial production and breeding priorities. In the most recent episode of low chill hour accumulation in the middle Georgia peach production area, a new all-time record appears to have been set, resulting in an inadequate chill hour accumulation for every commercial peach cultivar typically utilized in this production area. Some high chill cultivars received less than half of their required chilling resulting in widespread late bloom in combination with poor fruit set and vegetative bud break. Trees of nine high-chill cultivars displaying almost no bud break from last year’s shoots were used to study the effect of a late spray application (April 13^th) of hydrogen cyanamide on bud break. Cultivars tested differed significantly only in their lateral bud response, in terms of number of buds broken and peak time of bud break. ‘Ta Qiao’ showed the strongest response to hydrogen cyanamide applications, whereas ‘Julyprince’ the weakest. Peak impact on lateral bud break occurred in two weeks on long shoots (40-60cm) and in three weeks on short shoots (15-30cm). Across all cultivars tested, at the respective peak week the number of lateral buds that emerged on long shoots of treated trees was more than twenty times of that of untreated trees, whereas the number produced on short shoots of treated trees was about eight times of that of untreated trees; and at the seventh week after treatment the differences between treated and untreated trees became approximately two and four times, respectively, as more buds on untreated trees emerged at a slower pace. Almost no flower bud (<1 per shoot) opened prior to dry and drop on both treated and untreated trees. This experiment demonstrates that a late application of hydrogen cyanamide can help promote earlier and more lateral bud break, but had little effect on flower bud break or fruit set.