1-Naphthaleneacetic acid and 6-benzyladenine thinning of a common slender spindle ‘Jonagold’/M.9 apple orchard. II: Partial tree spraying

Abstract

SummaryMature slender spindle ‘Jonagold’/M.9 apple (Malus × domestica Borkh.) trees were thinned using 10 mg l–1 1-naphthaleneacetic acid (NAA) or 100 mg l−1 6-benzyladenine (BA) and an axial fan sprayer at a spray volume of 1,500 l ha−1 applied to the whole canopy, or with smaller volumes, where only the upper half of each canopy was sprayed. Partial spray applications of NAA or BA (at 1,000 l ha−1, 750 l ha−1, or 500 l ha−1) to the upper half of the trees did not cause any reduction in final fruit numbers on the upper half, or on the lower half of each tree. When the whole tree was sprayed to run-off with the same thinning agent, or at 1,500 l ha−1, successful thinning on both the upper and lower parts of the canopy occurred. Good spray coverage (from 51% to 77%) was also observed on leaves at all canopy positions measured, when whole trees were sprayed at 1,500 l ha−1.The development of an innovative crop load regulation strategy was an objective of the ISAFRUIT Smartfruit Project.