Influence of fumigation with high concentrations of ozone gas on postharvest gray mold and fungicide residues on table grapes.

To control postharvest decay, table grapes are commercially fumigated with sulfur dioxide. We evaluated ozone (O3) fumigation with up to 10,000 LL −1 of ozone for up to 2 h to control postharvest gray mold of table grapes caused by Botrytis cinerea. Fumigation for 1 h with 2500 or 5000 LL −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 fo r7da t 15◦C following fumigation. In a similar experiment, ‘Redglobe’ grapes were stored for 28 d at 0.5 ◦ C following fumigation for 1 h with 2500 or 5000 LL −1 of ozone. Both treatments were equal in effectiveness, but inferior to fumigation with 10,000 LL −1 . Ozone 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. Ozone was applied in three combinations of time and ozone concentration (10,000 LL −1 for 30 min, 5000 LL −1 for 1 h, and 2500 LL −1 for 2 h) where each had a constant concentration × time product (c × t) of 5000 LL −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 5000 LL −1 ozone for 60 min in a commercial ozone chamber and stored for 6 weeks at