Postharvest Control of Table Grape Gray Mold on Detached Berries with Carbonate and Bicarbonate Salts and Disinfectants

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The control of postharvest gray mold on detached table grape berries by treatment with carbonate and bicarbonate salt solutions, alone or with chlorine, ozone, or ethanol, was evaluated. Sodium carbonate (SC), potassium carbonate (PC), sodium bicarbonate (SBC), potassium bicarbonate (PBC), and ammonium bicarbonate (ABC) were tested without control of pH for their toxicity to spores of Botrytis cinerea in vitro, and the concentrations that stopped germination of 95% (EC95) of the spores were 16, 17, 36, 58, and 163 mM, respectively. When bicarbonate solutions were adjusted to pH 7.2 (±0.2), the mean EC95 concentrations for two B. cinerea strains of ABC, SBC, and PBC were 48, 102, and 112 mM, respectively. In 1.5 μg/ml of ozone in water, 50% and 95% mortality of spores of B. cinerea occurred after 21.3 and 35.6 sec, respectively. In tests to control gray mold on grapes, among the bicarbonates, each applied at 500 mM, ABC was significantly more effective than SBC and PBC. It was also superior to PC (100 mM) and chlorine (200 μg/ml) and equal in effectiveness to SC (100 mM) and ethanol (70% wt/vol). The addition of 200 μg/ml chlorine to the bicarbonate salts significantly decreased gray mold incidence. Ozone in water at 10 μg/ml significantly controlled gray mold, although its efficacy was irregular and dependent on grape condition. Among all the treatments, berry condition was an important factor; for example, there was significant decrease in control when wounded berries were treated compared to unwounded berries. The quality of grapes after treatment with ABC, SBC, ethanol, and chlorine was acceptable; ozone in water caused minor rachis injury; while severe injuries, mostly brown spots on berries, occurred after SC, PC, and PBC treatments.

F. Mlikota Gabler
J.L. Smilanick
American Society for Enology and Viticulture