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Perhaps this article will help: https://www.gardeningknowhow.com/edible/fruits/peach/brown-rot-fungus.htm

There is not much you can do except keep an eye on them. You may want to pre-treat the soil with fungicide to help keep root rot from setting in.

If you are having issues with drainage now, even if it is due to heavy rains, this indicates that you may want to amend the soil to improve the drainage.

This article should help: https://www.gardeningknowhow.com/edible/fruits/peach

These articles should helps with that: https://www.gardeningknowhow.com/plant-problems/pests/keeping-ants-of-flowering-vines-vegetables-and-flowers.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/get-rid-of-ants.htm

Thuricide can be sprayed on any plant, vegetable or fruit without posing a hazard. Bacillus thuringiensis (Bt) is another option. Since this is a selective insecticide, it kills tent caterpillars while remaining safe to humans. Here is an article that you may find helpful: https://www.gardeningknowhow.com/problems/pests/tent-worms-tent-caterpillar-home-remedy.htm

This is most likely lichen, and a symptom that the tree may be ill, as lichen usually like to attach to trees that are unhealthy. This article will explain more about lichen: https://www.gardeningknowhow.com/ornamental/fungus-lichen/treatment-tree-lichen.htm