I have found the most successful means of treating leaf curl on peaches and nectarines is spraying with a Trichoderma mix. The great benefit of this is that it is totally organic. Trichoderma is a naturally occurring  organic fungus which feeds on other fungus like that of Taphrina that causes leaf curl. Whereas copper sulphurs applications often defoliates the tree and kills other beneficial fungi, Trichoderma will only attack the area where the leaf curl is on the leaf, the remaining leaf section remains intact and continues to grow and photosynthesis in the normal manner. Regular applications of Trichoderma can eliminate leaf curl completely. Trichoderma should be applied at leaf burst and then 2 or 3 times through the season. However as a living organic substance Trichoderma cannot be applied in conjunction with chemical applications.

Trichoderma also works on other fungal problems like Apple Scab (black spot), rust on Silver Beet and Celery, Powdery Mildew on Grapes and Cucurbits. However in these cases it works better to treat the plants before the fungus is apparent.