One of the more significant fungal diseases in the Pacific Northwest on peaches is Peach Leaf Curl. Once the chill requirement for the peach tree has been met, the sealed bud scales “unzip” (the seal releases, but you will not be able to see any change), leaving them vulnerable to peach leaf curl infection. Peach leaf curl infections can only be prevented, control treatments are ineffective.
There are two primary methods of treatment. One is to apply lime sulfer fungicide three times, at two week intervals starting in late December through February in the Pacific Northwest but you need a dry day to do it., (Raintree Plant Owners Manual, pg 13). Time tables for treatment vary in different parts of the country; contact the co-operative extension office in your location for recommendations. Low chill varieties of peach may need even earlier treatment, see the November 2011 newsletter Insect/Disease Control section (under in the right side bar) for more information.
Another prevention method is to keep the stems of the tree dry. The peach leaf curl organism needs moisture on the stems to germinate and grow; keeping the stems dry prevents that growth. Put plastic (opaque or clear) over the tree, with supports to keep the plastic off the stems (condensation will make the stems wet), after the tree has gone dormant and before the buds have “unzipped”. Or train a tree against a wall under an eave where rain won’t contact the stems. Genetic dwarf peaches can be grown permanently in a container. Move the potted tree to a rain protected location, such as a carport or covered patio, during the cool wet infection period. An additional benefit to keeping the stems dry is you prevent other types of fungal disease infections that would normally also affect peach trees, such as brown rot or coryneum blight.
The easiest method would be to select a cultivar of peach that has some degree of resistance to peach leaf curl. Then you may only to need to spray during the first few years.