Relationship between Winter Air and Leaf Temperature and Cold Damage in ‘Bacon’ Avocado Tree

Abstract

In this study, the air temperature and leaf temperature of ‘Bacon’ avocado trees grown outdoors were measured in December and January to investigate the relationship with the occurrence of cold damage. Temperatures were recorded four times, three of which were clear weather with strong radiation cooling, and cold damage such as browning of leaves and defoliation had occurred. The minimum air temperatures when cold damage occurred were (from highest to lowest) -3.1 ℃, -4.5 ℃, and -5.1 ℃. The mean leaf temperatures in the early morning (at 4:00–7:00 am) on these days were -5.3 ℃, -6.9 ℃, and -6.9 ℃ respectively, and the respective differences between the mean leaf temperature and minimum air temperature were 2.2 ℃, 2.4 ℃, and 1.8 ℃. Based on these results, on early winter mornings with clear weather, the leaf temperature of the ‘Bacon’ tree was approximately 2 ℃ lower than the minimum air temperature. Leaf damage occurred when the mean leaf temperature was -5.3 ℃ or lower, which is consistent with the leaf temperature at which cold damage reportedly occurred in a previous indoor study. Our results suggest that the risk of cold damage in ‘Bacon’ avocado tree increases when the daily minimum air temperature falls below -3 ℃.