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Apple leaf drop, also known as Golden leaf drop and necrotic leaf blotch, is a physiological disorder common in Golden Delicious. It has also been noted on Jonagold, Gala and Gala/Splendour crosses. Leaf drop is not normally a serious problem. It is some-times mistaken for a disease or nutrient deficiency, resulting in unnecessary spray applications.
Symptoms: Symptoms may develop as early as June. Leaf drop or blotch appears as irregular brown blotches on mature leaves, often along the mid-vein. Blotches develop rapidly, usually within 24 hours. Leaf yellowing (below) and defoliation may follow within 4 to 7 days. Older trees are more likely to be affected than young, vigorous trees.
Figure 1. Apple leaf yellowed due to apple leaf drop disorder. (BCMA)
Cause: Apple leaf drop usually develops when a cool, rainy period of 4 to 5 days is followed by hot, sunny weather. It is thought to be related to temperature, light intensity and soil moisture effects on plant hormones.
Control: Control is not necessary as reductions in quality and yield have not been observed.