Symptoms and Signs
Gray mold infects flower parts at bloom time and remains quiescent (inactive) until fruit ripening. Typically, once the fruit is washed or stored at high humidity, water or condensation on the blossom end activates the fungal mycelium to begin growing. The pathogen sporulates on the flower parts and the typical grayish coating of spores develops. Eventually the crown tissue will be colonized, and the fungus will grow into the fruit tissue.
Infected fruit held in storage at high humidity often completely decays and shows the typical gray coating of spores; it may also have grayish-white mycelium and black sclerotia on the surface. Decay can also start from the stem end wound, especially if the stem is entirely removed.
Comments on the Disease
Gray mold is one of the most important causes of postharvest decay in pomegranates.
Botrytis spores reside in or on the soil and on previously infected plant tissue, weeds, and old fruit left on the tree or on the orchard floor (mummies). Spores are spread by wind. Spores landing on senescent flower tissues such as stamens (anther pollen sacks and filaments) germinate and produce an infection when there is free water on the plant surface from rain, dew, fog, or irrigation. Decay develops quickly when shelf temperature is about 65° to 75°F (18°–24°C).
Management
The extended flowering period of pomegranates makes bloom sprays for gray mold uneconomical and the fruit crown that covers the blossom prevents the use of preharvest sprays. However, postharvest sprays can be very effective.
Good orchard management practices, such as dust control and sanitation (removal of old fruit and dead branches), will reduce the postharvest incidence of disease.
Storing pomegranates properly can help avoid further decay by disease. The optimal postharvest storage temperature for pomegranates is 41°F (5°C) for up to two months and 45°F (7°C) for longer than two months. Store at 90 to 95% relative humidity. If storing for longer than three months, a controlled atmosphere of 5% oxygen plus 15% carbon dioxide is suggested.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| POSTHARVEST | ||||
| A. | FLUDIOXONIL | |||
| (Scholar) | 16 oz/100 gal | NA | NA | |
| MODE-OF-ACTION GROUP NUMBER1: Phenylpyrrole (12) | ||||
| COMMENTS: Liquid and dry formulations are available. For resistance management, treated culled fruit should not be returned to pomegranate orchards or other fruit crops orchards where fludioxonil is applied postharvest. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest. |
| NA | Not applicable. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to a fungicide with a different mode-of-action group number. |