Shoot pruning and treatment with hexaconazole or urea to increase fruit-set in olive

Traditional olive industry in Mediterranean area is affected by alternate bearing. This irregular production is enhanced by spring competition between shoot growing and fruit development on the same one-year-old branch. Total or partial cutting of the new shoots, as well as hormonal control of shoot growth with triazole may reduce vegetative flush and increase fruit set. Another strategy to favour fruit set is the treatment by foliar sprays with nitrogen fertilizers like urea during the period between full blossom and fruit ripening. In this paper foliar fertilization with urea is compared with hexaconazole treatment and with the partial or complete cutting of the new shoot growing on the fruit bearing branch, in order to evaluate the effects on fruit set and development. The research was carried out in 2005 and 2006 in the experimental orchard of AGRIS located at Villasor in southern Sardinia (39 degrees 21' of latitude North). Olive trees were planted in 1990, vase shaped and submitted to standard field management. Both shoot pruning treatments were effective in increasing fruit yield of the cultivar 'Bosana' (from 2.9 to 4.2% and 4.6% in 2005 and from 2.9 to 5.5% and 5.3% in 2006), 'Tonda di Villacidro' (from 1.5 to 5.3% and 4.8% in 2006) and 'Semidana' (from 3.4 to 3.9% and 4.4% in 2006), while 'Tonda di Cagliari' and 'Nera di Gonnos' cultivars showed statistically non-significant differences between fruit yield of test and pruned branches. Hexaconazole treatment was less effective than shoot pruning in increasing fruit yield and only for 'Bosana' (from 2.9 to 3.9% in 2006) a little positive effect was observed. Foliar sprays with urea were effective only with the 'Bosana' cultivar, increasing the rate of fruit yield from 2.9 to 4.3% of the flowers. No positive effects of urea treatments were recorded on 'Semidana' and 'Nera di Gonnos'.