Damage to Low-chill Peach and Plum Trees from Ice Accumulation during Severe Winter Freezes in North and North-central Florida

Abstract

Extreme cold during Jan. and Feb. 2009 required overhead irrigation for freeze protection of flowers and young fruit in the orchards at the Plant Science Research and Education Unit (PSREU) in Citra, FL, and the North Florida Research and Education Center–Suwannee Valley near Live Oak, FL. Severe freezes on 22 Jan. and 6 Feb. at both locations, with minimum temperatures of approximately 23 °F at Citra and 21 °F at Live Oak, and 10- to 11-h durations of sub-freezing temperatures each night, resulted in heavy ice loads. Additionally, there were 9 other freeze/frost events at Citra and over 20 events at Live Oak between 15 Jan. and 4 Mar. where overhead irrigation was used. Low-chill peach, nectarine, and plum cultivars were evaluated for limb breakage from excessive ice loads that resulted from freeze protection with overhead irrigation at both locations. Broken limbs with diameters greater than 7/8 inch (peach) or 1/2 inch (plum) and split scaffold limbs were counted on individual trees at Citra. Sample size per cultivar ranged from 2 to 47 trees. Trees were also rated for percent full canopy and percent full crop just prior to harvest. Peach and nectarine cultivars at Citra varied in the number of limb breaks and split scaffolds. ‘FlordaPrince’ had the highest incidence of scaffold limb splits (almost 3 per tree) while ‘UFSun’ had the highest incidence of limb breaks (approximately 5.5 per tree). No scaffold splits were observed for plum; however, the incidence of broken limbs was high (4 to 6.8 per tree) depending on cultivar. Percent full canopy just prior to harvest ranged from 60% (‘UFSun’ and ‘Gulfking’) to 80% (‘Earligrand’, ‘Sunraycer’, ‘FlordaPrince’, and ‘UFBeauty’) and percent full crop ranged from 10% (‘UFSun’) to 70% (‘Earligrand’ and ‘FlordaKing’). The greatest incidence of scaffold limb breaks at Live Oak was found in ‘Gulfruby’ plum (2.5 breaks per tree) and ‘UFQueen’ nectarine (3.0 breaks per tree).