Chemical Fruit Thinning of Apples
Most varieties will overset if bloom is heavy and bloom weather is good. Some varieties will consistently overset even if the weather is less than optimum. As a result, most varieties will need some thinning in most years in order to produce fruit of marketable size on a regular, annual basis.
New York State Agricultural Experiment Station
chemical apple thinning; thinning fruits chemically
New York's Food and Life Sciences Bulletin116