Endothall: A Blossom Thinner for Apples

Endothall [7, oxabicyclo (2,2,1) heptane-2-3 dicarboxylic acid] is an aquatic herbicide with potential use as a blossom thinner for apples (Malus domestics Borkh.). Trials conducted in Washington, New Zealand, and Australia on several apple cultivars indicate that endothall is a safe, consistent blossom thinner. Cultivars treated were `Golden Delicious', `Delicious', `Royal Gala', and `Granny Smith'. Single and repeat applications were used in the New Zealand and Washington tests. With multiple applications of endothall, no fruit marking occurred on any of the test cultivars. In temperate fruit zones with extended apple bloom periods, multiple applications of endothall at a low rate may be beneficial for reducing fruit set and biennial bearing.