Leaf spot and leaf drop of the apple cultivar Golden Delicious : a physiological disorder.
AbstractThe results are given of several experiments on the effects of temperature, daylength and light intensity on the incidence of leaf spot and leaf drop on young pot-grown Golden Delicious apple trees on M.9 The number of spotted leaves was much the highest at 21 deg C and declined successively at the following temperatures: 17 deg > 25 deg > 9 deg > 13 deg . Plants grown in sunlight had the fewest spotted leaves at most temperatures, and those grown under fluorescent light with 16- or 8-h photoperiods the most. Differential effects of high or low light intensities were slight. The oldest leaves on long shoots were usually the first to be affected. Foliar sprays of K, Ca, Mg, Mn or sugars did not affect the disorder, neither did soil moisture variation. (Abstract retrieved from CAB Abstracts by CABI’s permission)