EFFECTS OF 2,4-D, 2,4-DP, TRICLOPIR AND GA3 ON PRE-HARVEST FRUIT DROP AND SENESCENCE OF ´TAROCCO COMUNE´ BLOOD ORANGES IN SICILIAN ORCHARDS

Abstract

'Tarocco comune' blood oranges [Citrus sinensis (L.) Osb.] suffer from a heavy natural abscission and senescence of mature fruit. The present experiments were performed to reduce this problem and consequently to expand the harvest season and to improve fruit marketing. During the period of 2000-2004 we have studied in four field experiments the effects of several plant growth regulators (PGRs) on senescence and incidence of pre-harvest fruit drop of blood oranges. The best effects of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2,4-dichlorophenoxy) propanoic acid (2,4-DP), 3,5,6-trichloro-2-pyridyloxytacetic acid (triclopir) (45 to 10 mg L -1 ) and gibberellic acid (GA 3 ) (9.4 mg L -1 ) in delaying and reducing the undesired fruit abscission and senescence of 'Tarocco' blood oranges were achieved when sprays have been applied in October through December. GA 3 was found to delay changes in rind colour, an effect that can be considered either desirable or undesirable, depending on the harvest season. At harvest no residues of the PGRs were detected. However, currently only GA 3 and triclopir are authorized for pre-harvest use with citrus crops in Italy.