Answer: It sounds like your peaches are suffering from a fungal disease called peach leaf curl. It can affect leaves, flowers, tender shoots, and even fruit. Those diseased leaves will fall off soon, but unaffected leaves will grow normally. Infection occurs in spring when temperatures are around 68 degrees and surface moisture is present on the leaf buds. Therefore the problem doesn't occur every year with the same severity. Once you see the symptoms on the leaves it is too late to correct it for this season.
Sanitary measures can help control the disease, so it's a good idea to collect and discard fallen, affected leaves, and to prune twigs with the small, seldom-noticed swellings caused by the infection.
A minor infection won't harm the tree, but repeated or prolonged infection can weaken the tree. The lowest toxicity option for effective control is to apply a copper fungicide at the beginning of dormancy in the fall. Copper will cause the peach to defoliate so that is why we wait until the leaves begin to fall to apply it. Note that copper can stain masonry blue, so be careful in applying the spray if your tree is near a sidewalk, rock wall of your home, etc.
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