EFFECTS OF PACLOBUTRAZOL ON AVOCADO (PERSEA-AMERICANA MILL) CV FUERTE

Mature avocado trees (Persea americana Mill.) of cultivar 'Fuerte' were sprayed with Cultar®, a commercial formulation containing 25% paclobutrazol (ICI, U.K.). Hand spraying of individual trees before or at the flowering stage resulted in an increase in the number of harvested fruits per tree, reaching 97 and 174% above the controls in two groves. The phenological state of the bloom affected the results. The best additional yields, of 379 and 546% in two different groves, were obtained from sprays at the stages of elongating inflorescences and incipient anthesis. No residual or cumulative effect of Cultar® could be detected in two consecutive years of treatment with regard to tree vigour, general appearance, yield, or other factors. Application at 1000 l ha-1, by a commercial sprayer with a blower ('Spidet'), using 3% Cultar® resulted in a 90% increase in yield. The Cultar® sprays did not alter considerably the trends or the numbers of vegetative flushes during the season, but they did affect shoot elongation and 2% Cultar® caused a reduction of ∼ 30% in shoot length. The time lapse between fruit set and the start of vegetative growth was 4-5 days longer in the treated inflorescences. Cultar® may overcome the problem of low yields in trees which are considered to be of a clonal low-production type. The Cultar® sprays seem to increase yield in the "off" year in trees which bore a heavy yield in the previous "on" year. © 1990.