Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/2009
Publication Date: 10/21/2009
Citation: Gabler, F.M., Smilanick, J.L., Mansour, M., Hakan, K. 2009. Influence of fumigation with high concentrations of ozone gas on postharvest gray mold, quality, and fungicide residues on table grapes. Postharvest Biology and Technology. 55(2):85-90. Interpretive Summary: Table grapes rot after harvest unless actions are taken to retard this process. Sulfur dioxide gas is used to stop the rot, but it harms flavor and appearance of the grapes and leaves residues harmful to some people, so an ozone treatment of grapes was evaluated for this purpose. Ozone is a promising replacement for sulfur dioxide, it was moderately effective, caused minimal harm to the grapes, left no residues, and oxidized residues of several vineyard pesticides.
Technical Abstract: To control postharvest decay table grapes are commercially fumigated with sulfur dioxide. We evaluated ozone (O3) fumigation with up to10,000 microl/l of ozone for up to 2 h to control postharvest gray mold of table grapes caused by Botrytis cinerea. Fumigation for 1 h with 2,500 or 5,000 microl/l of O3 were equal in effectiveness: they reduced postharvest gray mold among inoculated ‘Thompson Seedless’ grapes by approximately 50% when the grapes were examined after storage for 7 days at 15 C following fumigation. In a similar experiment, where ‘Redglobe’ grapes were stored for 28 days at 0.5 C following fumigation for 1 h with 2,500 or 5,000 microl/l of O3 were equal in effectiveness, but inferior to fumigation with 10,000 microl/l. O3 was effective when grapes were inoculated and incubated at 15 C up to 24 h before fumigation. The cluster rachis sustained minor injuries in some tests, but berries were never harmed. O3 was applied in three combinations of time and O3 concentration (10000 microl/l for 30 min, 5000 microl/l for 1 h, and 2500 microl/l for 2 h) where each had a constant concentration x time product of 5,000 microl/l x h (c * t). The effectiveness of each combination was similar. The prevalence of gray mold was reduced by approximately 50% among naturally inoculated, organically grown ‘Autumn Seedless’ and ‘Black Seedless’ table grapes, and by 65% among ‘Redglobe’ table grapes, when they were fumigated with 5,000 microl/l O3 for 60 min in a commercial O3 chamber and stored for 6 weeks at 0.5 C. Residues of fenhexamid, cyprodinil, pyrimethanil and pyraclostrobin were reduced by 68.5, 75.4, 83.7, and 100.0 percent, respectively, after a single fumigation of table grapes with 10, 000 microl/l ozone for 1 h. Residues of iprodione and boscalid were not significantly reduced. O3 is unlikely to replace SO2 treatments in conventional grape production unless their efficacy is improved, but it could be an acceptable technology to use with grapes marketed under “organic” classification, where the use of SO2 is prohibited, or if SO2 use is discontinued for some reason.