This page was prepared mainly by the senior author as part of a project for ENT 4987, Arthropod Management in Fruit Crops. It is important to thin apple trees to achieve optimum fruit growth and enhance tree vigor. Proper thinning also reduces limb breakage. An overloaded apple tree will produce many small, low value fruit, whereas a tree that only has several fruit is not producing to its maximum potential. Insufficient thinning may also lead to alternate bearing, an event where an extremely heavy crop will not produce any fruit the following year.
Many different factors can affect the success of the chosen thinning practices.
Combinations of several chemicals, such as Vydate, Sevin, NAA, and Accel often work the best. However, there is no single outstanding combination with which to thin. Some treatments may require several applications. With this in mind, thinning apple trees becomes more of an art than a science. Although several different methods of physical or chemical mechanisms can be utilized to accomplish the same result when thinning, the following information will concentrate on chemical tools available for thinning.