Sulfur is not very effective against peach leaf curl (lime sulfur is effective but is not registered for use in home gardens in Oregon). Two fungicide applications are recommended for peach leaf curl, one in the fall at about 50% leaf fall (late October to early November) and the second in the dormant season just before floral buds begin to open (which is usually in late February). As a home gardener, your best options are chlorothalonil or a copper based fungicide, and chlorothalonil is the more effective fungicide of the two. You can find more information on Managing Diseases and Insects in Home Orchards in OSU Extension publication EC631 https://catalog.extension.oregonstate.edu/ec631.