Suppression of Olive (<i>Olea europaea</i> L.) tree growth by uniconazole in high-density orchards

Abstract

High-density olive orchards (1000–3000 trees/ha) allow use of the continuous straddle harvester that rides over the tree canopy, and enables very low harvesting and labor costs. However, tree size must be controlled, to enable the harvesting machine to pass over the hedgerow, and also to ensure light penetration into the tree canopy. High-density-planted ‘Picholine’ and ‘Koroneiki’ olive trees, aged 5 to 6 years, were treated with the gibberellin biosynthesis inhibitor uniconazole for two consecutive years to reduce their growth rates. Two methods of uniconazole application were used: soil application at 0.1 or 0.2 g/tree, and foliar sprays at 0.75 and 1.5 g/tree. The soil treatments reduced trunk-width increment and tree height in both cultivars as soon as the end of the first year, whereas foliar treatments failed to affect these parameters. In both cultivars, neither application influenced shoot or leaf development in the first year of the experiment, but ‘Koroneiki’ shoot elongation was inhibited by b...