Answer: It sounds as though powdery mildew is attacking your tree. It is a fungus and it can spread rapidly. You can prune away the affected foliage and apply a fungicide to protect the healthy foliage from the fungus. Your tree should be old enough to get by on one or two deep waterings a week (two in the hottest months of the year, one the rest of the time). Be sure to clip off the dead foliage and any leaves with the whitish powder and remove them from the garden to slow the spread of the disease.
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