Relative Effectiveness of Dilute and Concentrated Abscission-chemical Sprays in Loosening ‘Valencia’ Oranges from Trees1

Abstract Ethylene production, hydrolytic enzyme activity, and fruit removal force (FRF) were more uniform and consistent when abscission chemicals were applied as dilute as compared to concentrated sprays to ‘Valencia’ orange ( Citrus sinensis (L.) Osbeck). Cycloheximide (Acti-Aid), glyoxal-dioxime (Pik-Off), 5-chloro-3-methyl-4-nitro-1H-pyrazole (Release), and Acti-Aid plus chlorothalonil (Sweep) were applied to ‘Valencia’ orange branches, each holding 100 to 120 fruit. The FRF's resulting from commercial concentrate and dilute sprays of Acti-Aid and Acti-Aid plus Sweep were similar to those in the branch tests. Equal amounts of chemical were applied in the dilute and concentrate sprays. Likely, the variation in coverage from concentrate sprays caused ethylene levels to vary greatly in the fruit (0 to 5.7 ppm). In turn, levels of hydrolytic enzyme activity varied as much as 10×, and fruit loosening was inconsistent (0 to 9.7 kg FRF). Release and Acti-Aid plus Sweep were more consistent than Pik-Off and Acti-Aid in dilute spray applications.