An Analysis of Historical Freeze Events and Determination of Blueberry and Peach Critical Bud Temperatures to Aid Growers in Freeze-related Risk Assessments

Freeze damage can result in significant economic losses for growers of low-chill blueberry (Vaccinium spp.) and peach (Prunus persica L.) in subtropical climates. Freezes can be categorized as either radiative or advective. Radiation freezes are characterized by clear skies, winds less than 5 miles per hour (mph), and the development of a temperature inversion layer. Advective freezes are characterized by winds greater than 5 mph, cloudy skies, and the absence of a temperature inversion layer. The objective was to use historical weather data and to determine the critical temperatures for peach and blueberry floral buds in order to provide growers with additional information for their risk assessment decision-making process. Weather data from 2000-2015 for three Florida locations, Alachua, Lake Alfred, and Frostproof, were downloaded from the Florida Automated Weather Network (FAWN) and analyzed. Hourly temperature, wind speed, dew point, and relative humidity were used to determine the average number of days annually with sub-zero temperatures, the average of number of days per month with sub-zero temperatures, the duration of each freeze event, and to classify each event as a radiation or advective freeze. Additionally, preliminary analyses of critical bud temperatures for two low-chill peach and blueberry varieties were conducted using differential thermal analysis (DTA) and standard freezing tests during the fall and winter of 2014-2015. Preliminary DTA results do not show a consistent correlation between the low temperature exotherm and lethal bud temperature determined by the standard freezing tests. This could be in part due to the low-chill varieties not fully entering into endodormancy. DTA will be continued into the future and the results will be compared against controlled freezing tests.