You are not going to have to be a rocket scientist for this one. Peach leaf curl targets only peach trees and nectarine trees and it is pretty easy to spot. It is, by far, one of the worst diseases your peach tree could have and it usually occurs in the springtime when the weather is cool and wet.
New peach leaves will be very thick (abnormally so) and, as they grow, they begin to curl and have a "puckered" look to them. On the leaves, you will find blisters that will later turn white. The blisters will usually start out as yellow or reddish. Later, the whole leaf can turn different colors while at the same time developing a whitish covering.
In early summertime, those already-ugly leaves will get even uglier, as they turn black, shrivel up completely and fall. Sometimes, after the infected leaves fall, another crop of leaves can form on the tree, but trees that are infected are weak and produce fruit (if you get any) that will be misshapen and covered with lesions in varying shapes.
This fruit will drop before it ripens and several years of the disease will make your peach tree severely weak with a reduction in the amount of fruit you are able to find usable. Usually, the tree won't die, but you may wish it would.
Peach Leaf Curl at Its Worst
Preventing Peach Leaf Curl
There are certain varieties of peach and nectarine trees that are resistant to peach leaf curl, and I suggest you seek those out in whatever zone you are in, as I expect different varieties will be more or less resistant depending on your zone.
If you have had peach trees in the past that were infected with peach leaf curl, you should always use a dormant-season fungicide that contains lime sulfur spray or a Bordeaux mixture, but wait until the last leaf falls, then spray them again in the spring before new leaves appear. If you wait until buds are open on the tree before using a fungicide, you have waited too long.
Managing Peach Leaf Curl
Once a leaf is infected, there is no cure. You must remove them and destroy them, but do NOT put them in your compost heap. You must use preventive measures outlined above.
This particular disease has ruined peach crops in the United States for over 100 years and it most likely isn't going to go away any time soon.