Thinning apples via shading: an appraisal under field conditions

Fruit development and fate was followed on “Imperial Gala” trees thinned chemically or via shading. Fruit % drop, fruit growth rate via caliper and electronic gauges, whole tree gas exchanges were measured before, during and after treatment with 9% neutral density shading cloth. Shading was applied for 1 week starting 30 days after full bloom. (DFAB). Whilst the fruit were thinned to similar crop loads and reached similar size at harvest, their growth patterns reflected the treatments applied, with fruit slowing down and dropping sooner in the chemically thinned fruit (which were treated earlier), and then in the shading treatment, which took place later. Fruit daily growth patterns were changed and greatly reduced under shading, as were three net carbon exchange rates, both total per tree and per unit of light intercepted by the trees. A regression analysis between the NCER per unit light intercepted revealed no difference between the two treatments before and after shading, but a significantly lower relationship during shading. This work supports the hypothesis that C-starvation may induce fruit abscission around 30 DAFB. Fruit growth patterns and their changes during shading were consistent with this hypothesis. Before this method of thinning, which may be interesting for a reduced use of chemicals, or in organic fruit growing, may be adopted, a method of gauging the length of the shading period is needed