What postharvest diseases affect grapes grown in a high tunnel?
Answer: Grey mold (Botrytis cinerea) is the most significant postharvest disease of table grapes. The fungus can develop at temperatures of 31°F and spread from one grape to another in a cluster (Crisosto and Mitchell, 2002). It is identified at first by the “slipskin” condition that develops on some berries and later by “nests” of decayed berries covered in a white fungal mycelium. Botrytis rot can be controlled by the introduction of sulfur dioxide (SO2) gas during forced-air cooling, though this method is impractical for small-scale growers and not allowed in organic production. The use of ozone gas shows promise as an alternative to sulfur dioxide for organic growers (Gabler et al., 2010).
Other postharvest diseases that can affect grapes include black rot, ripe rot, Macrophoma rot, powdery mildew, blue mold, Alternaria, and Cladosporium rot (Slama and Diffley, 2017). Shatter can also occur postharvest, caused by rough handling, packing clusters too deep, or improper storage temperatures. Controlling packing density, maintaining the correct storage environment, and using cluster bagging can all help prevent postharvest shatter (Crisosto et al., 1998).
ATTRA recently produced a series of five publications on high tunnel grape production, which you should find useful. The titles in the series are:
Crisosto, Carlos H., and F. Gordon Mitchell. 2002. Postharvest Handling Systems: Small Fruits. In: Adel A. Kader. Postharvest Technology of Horticultural Crops. Regents of the University of California Division of Agiculture and Natural Resources, Oakland, CA.
Gabler, Franka Mlikota, Joseph L Smilanick, Monir F. Mansour, and Hakan Karaca. 2010. Influence of fumigation with high concentrations of ozone gas on postharvest. Postharvest Biology and Technology. February. p. 85-90.
Slama, Jim, and Atina Diffley. 2017. Wholesale Success: A Farmer’s Guide to Food Safety, Selling, Postharvest Handling, and Packing Produce. FamilyFarmed, Chicago, IL.