Answer: White spots on leaves should be distinguished from the white or light gray powder caused by Powdery Mildew. The white spots, which are symptomatic of the problem, appear as part of the leaf tissue. The white or light gray powder caused by Powdery Mildew is a fungus which covers the leaves superficially. Even though you do not see insect pests, they may be so tiny that you'll need a magnifying glass to identify them. Thrips can cause the spots you describe. Until you know for sure what the problem is, probably the best course of action is to wait until next spring and prune off all the affected leaves. Or, you can take a few of the leaves to your local Master Gardener clinic or cooperative extension office for help with diagnosis and control measures. Best wishes with your landscape.
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