I'm a novice at this, but really, you should be thinning your fruit when it is small so you don't get to this stage. As for pruning, I think the best time to do it is in late winter, or very early spring. You can do summer pruning (and I do do some), but it has a tendency to slow down the tree's growth. -Glenn

On the intact branches I would thin the fruits by removing the excess. I space my peaches about 10 inches apart. More if the branch can't support it.

You can also follow the "Backyard Orchard Culture" which suggests pruning/thinning in the summer when the fruit is bearing as seen below (but probably not when the fruit is too big).. I'll be trying this out on a plum tree this weekend..

Here is a link that might be useful: Backyard Orchard Culture

Love2garden:

You don't say where you are located, so I can't get a feel for the developmental stage of your fruit, but yes, you can prune peach and plum trees early to open them up to light on the fruit. I do it all the time, every season. In the process of pruning, you will inevitably remove some fruit and relieve weight on the branches.

But pruning is no substitute for thinning the fruit, both peaches and plums. I thin off at least 90% of the fruit on my peaches, and maybe 80% of the plums, and sometimes this is not enough if they are still too closely spaced. Always try to leave behind the largest, fastest growing fruit, since they will be the best, but if there are two big ones right next to one another, one of them has to go.

If your trees are too tall to reach all the fruit from your ladder, prune them down so that you can. Crowded fruit at the top of the tree will not be full size, and can cause limb breakage.

Don Yellman, Great Falls, VA

Thanks for your help guys, I'm pruning a little bit at at time. Wish I had thinned but, like I say, the squirrels normally take care of that for me when the fruit is still very small and now there are thousands of plums on the tree ! This tree is tall and very large and actually, half of it is peaches ! I call it my
"pleach" tree. The limbs are draping so drastically they are touching the ground, reminds me of a huge umbrella.
osxaddict, Thanks for the link-great info. there !
Don, I am in N.C. so my fruit is prob. in the same stage as yours is about now.