zebrin wrote:

Reasons for many (not all) peaches falling off?

Zebrin

A natural thinning of the fruit. There is an ideal ratio of foliage to
fruit which encourages the development of large, robust and juicy fruit
and reduces the biennialism of many fruit trees. Most fruit trees will
go through this process naturally, shedding the excess small,
undeveloped fruit, but commerical orchardists have this down to a
science, using both chemical and manual means to optimize and space the
fruit to generate the best crop and maintain the health of the tree. In
short, some early fruit loss is entirely natural and a good thing.

pam - gardengal