Abscission chemicals for Valencia oranges in New South Wales

Abstract

Three abscission chemicals inducing production of ethylene, have been evaluated as aids for mechanical harvesting of Valencia oranges at Horticultural Research Stations at Gosford (coastal) and Dareton (inland) in New South Wales during 1971-75. Ethephon (CEPA) promoted abscission without visible injury to the fruit but leaf drop at concentrations required to give adequate loosening (500 p.p.m.) was excessive. Cycloheximide (CHI) at 20 p.p.m. reduced fruit removal force (FRF) to 3.2 kg at Gosford and to 4.6 kg at Dareton in 1971, and again to 3.7 kg at Gosford in 1972. There was no reduction in FRF at Dareton in 1972. The addition of Polycote (R) (polyethylene emulsion) to CHI at Gosford enhanced theabscission response by reducing FRF an additional 20 per cent. Spraying before or after irrigation at Dareton; or during December, January or February at Gosford had no effect on FRF. Leaf and fruitelt drop caused by CHI were too high for commercial practice. Release (R) (CMNP) was selective for mature fruit only, and at concentrations up to 300 p.p.m. no fruitlet or leaf drop occurred while FRF was reduced to between 2 kg and 4 kg. This chemical was the most promising for incorporation into a mechanical harvesting system, but because of damage to the rind is limited to fruit for processing only.