Fruit thinning guided by physiological principles

D.W. Greene
Chemical thinning is an essential component required for successful and profitable apple production. Thinning studies have been going on since the 1930s but meaningful progress toward consistent and reliable crop load adjustment was slowed by our incomplete understanding of the way thinners work and the physiology of early fruit abscission. When the focus of research started to switch from the primarily empirical approach to studies that provided insight into the mode of action of thinners and identifying the environmental factors that most affected fruit set, greater progress was achieved. Scientist also recognized that as fruit development progressed from bloom through the 25 mm fruit size stage, requirements to thin adequately also changed. Therefore, different thinning strategies had to be developed for each developmental stage. Light and temperature were important factors that affected thinning through their influence on carbon balanced in a tree. The slowing of fruit growth on fruit destined to abscise was recognized and used as an accurate and successful prediction tool for final set. Trees illuminated with low intensity of red light (660 nm) from bloom until the end of June drop resulted in increased fruit set caused primarily by retardation of June drop.
Greene, D.W. (2017). Fruit thinning guided by physiological principles. Acta Hortic. 1177, 41-50
DOI: 10.17660/ActaHortic.2017.1177.4
Malus × domestica, fruit set, chemical thinning, abscission, carbon balance, fruit growth model

Acta Horticulturae