2017 ASHS Annual Conference

Temperate deciduous fruit trees such as peach and nectarine (Prunus persica) require winter cold to complete endodormancy so that flowers set and leaves emerge normally in the spring. Climate aberrations in recent years has resulted in inadequate winter cold for some traditional late blooming (high chill requirement) cultivars with the result being poor flower set and irregular vegetative bud break. The past two Southeastern winters have not provided sufficient cold for as much as half of the commercial peach cultivars. With on-site weather data and models to calculate chill hours, units or portions, the amount of winter chilling can be monitored and several horticultural practices can be implemented to lessen or avoid a crop loss. Southeastern U.S. peach growers can access from NOAA projected January-February temperatures in El Nino or La Nina years to determine if chilling might be insufficient. At this time dormancy breaking chemicals such as hydrogen cyanimide, potassium nitrate or calcium ammonium nitrate should be considered for use. Timing and rates are critical for these compounds. Other management tools may be necessary if dormancy issues persist into late winter. These include prune as late as possible to delay cambial activity as the inadequately chilled buds are biologically sluggish. Retain more interior short shoots as those buds have lower chilling requirement. On trees with no visible flower bud activity, do not prune until vegetative buds emerge to determine if sufficient new shoots will develop for next years’ crop. Do not thin marginally chilled trees until fruit begin actively growing so that good fruit can be differentiated from those that will never size (i.e., buttons). Trees with no crop and have poor vegetative bud break can be treated in spring with dormancy breaking agents as a salvage treatment to prevent tree decline or death. Future dormancy breaking technologies and replacement of cultivars with ones having lower chilling requirements will be necessary to grow peaches successfully in an increasing warmer climate in the 21^st Century.