Ethylene and Fruit Loosening from Combinations of Citrus Abscission Chemicals1

in Journal of the American Society for Horticultural Science
Authors: R. E. Holm1 and W. C. Wilson2
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  • 1 Diamond Shamrock Corporation, Painesville, Ohio 44077
  • | 2 Florida Department of Citrus, Lake Alfred, Florida 33850


Two and 3-way combinations of 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), cycloheximide (Acti-Aid), and chlorothalonil (Sweep) were extensively evaluated for fruit abscission and ethylene production responses on ‘Hamlin’ and ‘Valencia’ oranges (Citrus sinensis (L.) Osbeck). The combinations interact synergistically resulting in far greater fruit loosening than would be expected from additive effects of the individual chemicals. The 3-way combinations of Release plus Acti-Aid plus Sweep consistently gave better fruit abscission than the 2-way combinations of Release plus Acti-Aid and required 25% to 50% less abscission chemical compared to individual abscission chemical usage. Increased fruit abscission activity of the chemical combinations resulted from greater peak fruit ethylene production and higher sustained ethylene levels during the treatment period. Distinct fruit loosening and retightening phases were characterized and shown to be correlated with internal fruit ethylene levels.

Contributor Notes

Received for publication March 6, 1977.