Chemical thinning of ‘Barouni’ and ‘Manzanilla’ olives with naphthalene acetic acid under South African conditions

Abstract

Table olives grown in the Mediterranean-type climate of Western Cape province of South Africa are prone to alternate bearing, as elsewhere in the world. To date, South African producers have tolerated the negative effects of alternate bearing, but due to increased olive production costs, profit margins are decreasing and producers have to reduce alternate bearing. Trials were conducted to evaluate the use of naphthalene acetic acid (NAA) on ‘Barouni’ and ‘Manzanilla’, the most important green table olive cultivars grown in South Africa. NAA is used elsewhere in the world, but local research is required since the efficacy of NAA is modulated by environmental conditions and genotype. NAA decreased the fruit number per tree, thereby improving fruit size in both cultivars. Thinning did not affect return bloom in ‘Barouni’, possibly due to the low level of thinning achieved, whereas adverse climatic conditions during flower development may be to blame for the lack of return bloom in ‘Manzanilla’. Although NAA application did not affect the income per hectare, profitability may increase as harvesting costs account for roughly 50% of the input costs. Based on these results, 200 mg L⁻¹ NAA, applied 10–15 d after full bloom, is recommended for local conditions.