S16 - Session P2 - Defoliation of apple trees before harvest influences red skin colour and ripening

Authors: Konni Biegert *, Roy McCormick

Partial defoliation of apples trees prior harvest is an emerging grower practice in the Lake Constance area to increase the red skin colour of fruit. Tractor mounted machines using air pressure jets are now available for this purpose. With increased light exposure fruit colour developed is increased. In the season 2021, we conducted mechanical pruning and leaf defoliation treatments seven to 14 days before harvest on the two bicoloured apple cultivars 'Elstar' and 'Kanzi'. Trees were approximately 3,70 m high and in full crop. The Streif maturity index was used to determine harvest timing. Grading results for the percentage red skin colour area, fruit diameter and weight together with the amount of fruit removed at each harvest and the speed of harvesting will be presented. The efficacy of preharvest leaf defoliation to increase the amount of marketable fruit will be discussed.