The lack of a good thinning program on peaches will result in excessive numbers of small, poor-quality fruit and may cause tree breakage due to the weight of the crop. Trees carrying an excessively large crop will become less vigorous and more susceptible to disease and cold injury. Not thinning or thinning too late in the summer may cause trees to alternate bear; however, this tendency is not as pronounced in the South, compared to more northern production areas.
Thinning the crop early in the growing season can promote increased size in the remaining fruits as a result of increased cell division in the early stages of fruit growth. The later the thinning process, the less effective it will be.
Healthy peach trees usually set far more fruit than the tree should be allowed to carry. There are periods of natural fruit drop in peach with the June drop (which occurs in May) being the most important. Competition among the developing fruits for stored food reserves and the current season’s photosynthates will force the tree to shed the smaller, weaker fruit. Unfortunately, the June drop usually doesn’t result in adequate fruit thinning, and the time of this drop is too late to provide the maximum increase in size of the remaining fruits. The urge to delay thinning until after
the June drop should be resisted in order to gain the maximum results from thinning.
While there has been a lot of work on methods of thinning peach fruit utilizing growth regulators, products that burn the blooms, and removal of blossoms and fruits by high pressure water and mechanical shakers, most of the peach thinning in Tennessee is done by hand. Jarring limbs by striking them with padded sticks or plastic bats can dislodge many peach fruits and lessen the crop load; however, it does not remove the smaller or defective fruits. Follow-up hand thinning may be needed to break up clusters and to remove fruits that have blemishes or damaged areas.
Thinning the crop is a time-consuming, expensive operation, but it is essential most years if you hope to obtain high-quality, large fruit on a consistent basis.