How can I prevent black spots and leaf drop on my peach trees?

This may be a fungal infection or possibly two different fungal infections that are not affected by copper treatments. The timing of fungicide treatments is also extremely important. Generally, the first application should be at budbreak for fungal diseases affecting the foliage. Fungal diseases affecting fruit require different timing, but still early is better. During dormancy, the best things to do are cleaning up foliage debris from the ground, fertilizing, and pruning.