Removing excessive numbers of tiny peaches in spring from the tree branches yields two benefits. Dr. John Pyzner of Louisiana State University mentions that reducing the developing fruit clusters on peach tree (Prunus persica) branches allows for higher quality fruit development and prevents branch breakage from heavy crop loads. Selectively pruning off small peaches a month after the flowering ends can be time-consuming. Plucking off peaches as late as a couple weeks before they are ready for harvest can still improve the flavor and final size of the peaches that remain on the branches, too.
Gently shake the peach tree's branches in early spring to cause some flower buds and flowers to drop off the branches. You need to vigorously jar the branches, but don't place so much pressure on them that they crack. Dr. Pyzner mentions that peach trees naturally tend to over-produce, so losing some flowers helps diminish the subsequent number of fruits in a few weeks.
Repeat gentle shakes of the peach tree's branches once the early spring flowering wanes. This will drop petals as well as any weak-stemmed developing fruits. You can withhold the shaking until you see small peaches the size of peas on the branches and then shake them every couple of days to shed them.
Clip away small developing peaches from the branches about four to six weeks after the flowering ends--a process called "thinning out." By this time you will be able to readily see the peach fruit clusters and spacing of fruits across the tree's canopy. Use heavy-duty scissors or other narrow-bladed cutting instrument to snip out peach fruit stems. Leave one peach, spaced every 4 to 6 inches, along the length of branch.
Monitor the development of the peaches on the tree in late spring and early summer, removing any deformed or damaged peach fruits. You can thin out peaches until two to three weeks before that variety's expected ripening date in your area. Don't rely on this late-term thinning to ensure your developing peaches are of the best size and quality.