Approximately 3-5% of perennial orchard trees are replanted annually. Bearing fruit on newly planted orchard trees is undesirable because fruits are strong carbohydrate sinks and compete with shoot growth, and thus limit early growth of orchard trees to fill their space. Therefore, manual removal of flowers and fruitlets from newly planted trees has been practiced. In almond, leaving nuts on young trees cannot just limit vegetative growth but also serve as harboring site for navel orange worm. Therefore, removal of flowers and fruitlets/nutlets via spray application of chemical thinners would be highly desirable to aim tree growth and reduce manual labor cost for tree defruiting. In a series of experiments in nectarines, almonds and walnuts in California, we investigated the effects of the application of ACC alone or in combination with S-abscisic acid (S-ABA), 6-benzyladenine (6-BA) on flower and fruitlet/nutlet removal. Results indicated that ACC by itself at 450-600 mg/L or in combination with 300 mg/L S-ABA or 400 mg/L 6-BA can effectively defruit young orchard trees and reduce manual labor cost. No phytotoxicity was observed in any of the trials.
