To control postharvest decay, table grapes are commercially fumigated with sulfur dioxide. We evaluated ozone (O₃) fumigation with up to 10,000μLL⁻¹ of ozone for up to 2h to control postharvest gray mold of table grapes caused by Botrytis cinerea. Fumigation for 1h with 2500 or 5000μLL⁻¹ of ozone were equal in effectiveness. Both treatments reduced postharvest gray mold among inoculated ‘Thompson Seedless' grapes by approximately 50% when the grapes were examined after storage for 7 d at 15°C following fumigation. In a similar experiment, ‘Redglobe' grapes were stored for 28 d at 0.5°C following fumigation for 1h with 2500 or 5000μLL⁻¹ of ozone. Both treatments were equal in effectiveness, but inferior to fumigation with 10,000μLL⁻¹. Ozone was effective when grapes were inoculated and incubated at 15°C up to 24h before fumigation. The cluster rachis sustained minor injuries in some tests, but berries were never harmed. Ozone was applied in three combinations of time and ozone concentration (10,000μLL⁻¹ for 30min, 5000μLL⁻¹ for 1h, and 2500μLL⁻¹ for 2h) where each had a constant concentration×time product (c × t) of 5000μLL⁻¹ ×h. The effectiveness of each combination was similar. The incidence 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 5000μLL⁻¹ ozone for 60min in a commercial ozone 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%, respectively, after a single fumigation of table grapes with 10,000μLL⁻¹ ozone for 1h. Residues of iprodione and boscalid were not significantly reduced. Ozone is unlikely to replace sulfur dioxide treatments in conventional grape production unless its 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 were to be discontinued.
