Effect of ringing and spraying with gibberellic acid and mineral oil on the fruiting of young 'Monte Parnaso' navel orange trees

Abstract

Aiming to study fruit set increase of young 'Monte Parnaso' navel orange trees (Citrus sinensis Osb.), plants were sprayed with 0, 10, 20, or 30 ppm of gibberellic acid (GA₃) solution, plus 0 or 1% of mineral oil. Two experiments were set up: one spraying the trees twice, on 22^nd and 29^th of July, 1993, and another spraying the trees on 15^th of September, 1993, when it was all at full bloom. In both experiments 50% of the trees were ringed 5 cm down the first branch of the crown. Results showed that fruit production decreased linearly with the increasing of GA₃, applyied on 22^nd and 27^th of July, 1993; there was no significant effect for GA₃ applyied at full bloom. The spraying of 1% mineral oil decreased harvest by 42%, mainly when applyied at the end of July. Ringing increased fruiting nearly to 25% and decreased the average fruit size.