Chemical treatments in order to increase fruit-set on three olive cultivars.

Lack of sufficient fruit-set and consequent irregular yield is a common problem of many olive cultivars like ‘Bosana’, ‘Nera di Gonnos’ and ‘Semidana’, which are among the most important olive cultivars in Sardinia Island (Italy). In the growing season 2016/2017 a field experiment was designed in the experimental farm of Villasor (South Sardinia). Mature trees of the three cited cultivar in the stage of full blossom were submitted to treatments with the following bio-stimulants substances: Gibberellic Acid (12 ppm); EVEO® (1 ml/l; by Thermaflora, which contains 770 g/kg of polyethylene-glycols and 3 g/kg of humic salts of plant origin); water test. Four plants were used for cultivar and treatment and inside every plant 12 flower-bearing (20-30 inflorescences) branches were selected considering the 4 cardinal points and 3 levels of height in the canopy. Fruit-set as percentage of the counted flowers was observed in June, and in July and September the count of the developing fruits was repeated. Tree of ‘Nera di Gonnos’ showed little benefits consequent to treatments on the fruit-set level observed at June but any treatment had a permanent positive effect until harvest. ‘Semidana’ cultivar showed the highest natural level of fruit-set and a little positive effect of treatments on the percentage of harvested fruit. The cultivar ‘Bosana’ showed the highest benefits of the treatments with the good influence on fruit-set and a moderate influence on the harvested fruits.