Chemical and Defoliation Effects on Fruitset of \"Cox Orange\" and \"Elstar\" Apple Cultivars

Abstract

Experiments were carried out at Klein Altendorf station in 2001 and 2002 with the objectives to reduce the number of fruits per tree, improve fruit quality and yield, overcome biennial bearing and investigate how photosynthesis and transpiration are affected by one of the chemical thinners (i.e. Azolon). At a dise of 10mg a.i/Li Ethrel (Flodimex) thinned better than at 5mg a.i/Li in 2001 while at 3 mg/Li in 2002 it achieved the required fruit set by thinning before June drop 62% and 15% after June drop compared to 49% of the unsprayed control and had 71% of the fruits in the class 1 fruit diameter size range
of 75 to 90mm while yield per tree was reduced by 31% by Ethrel at 10mg a.i/Li but not Ethrel at 5gm a.i/li which had no effect on yield. Mean fruit weight was unaffected by the treatments. The foliar urea based fertilizer Azolon fluid at 75mg a.i/Li applied at full bloom, resulted in 61% fruit set before and 17% after June drop in 2002, slight leaf yellowing, killing
and epinasty 7 days after treatment application which disappeared 14 days later but probably started earlier and a slight reduction in leaf photosynthesis and transpiration rates. However, Azolon fluid (i.e. methylene urea or urea formaldehyde) yielded smaller fruit than Ethrel (Flordimex), but larger fruits than the untreated control trees, without affecting fruit yield. The partial and gradual defoliation of selected primary spur leaves reduced fruit set to 50% before and 14% after June drop. These results provide evidence that reductions in photosynthetic rate or photosynthetic leaf area during the period of flowering is sufficient and can successfully induce thinning with a commensurate efficacy to chemical thinners.

Keywords: Growth regulator, chemical application, full broom, fruitset, defoliation, natural and induced fruit drop, apple tree, photosynthesis, transpiration, yield, fruit drop, Azolon, Ethrel, Frodimex

Discovery and Innovation Vol. 19 (1) 2007: pp. 56-59