Studies on the Cold Wind Damage of Citrus Trees

Abstract

Data about the defoliation of citrus leaves were analysed statistically to clarify the relationships between the defoliation rate and meteorological elements such as wind velocity, air temperature, and humidity.The data concerning the defoliation of citrus leaves and meteorological conditions were obtained in a citrus orchard at Shizuoka prefecture during the period from January to March in 1959.The results so obtained may be summarized as follows:The defoliation rate was found to be related closely to the maximal wind velocity and the mean air temperature of the day on which the defoliation occurred. The correlation coefficient between the defoliation rate and the wind velocity was positive, and that between the rate and the air temperature was negative. The defoliation percentage (D) was approximated byD=α(U-a)(b-T)+c, where, U is the maximal wind velocity (m/sec), T the mean air temperature, a the constant varying from 6.5 to 8, b the numerical constant with the value of 1.5, c the constant with the value of 0.25, and α the constant ranging from 0.10 to 0.15.This empirical formula indicates that the defoliation of citrus leaves is affected by both the wind velocity and the air temperature of the day on which the defoliation occurs. Comparing the defoliation rate with the seasonal change of the temperature, it was found that meteorological conditions at one month before the defoliation occurred also gave a significant influence on the defoliation of citrus leaves.