Symptoms and Signs
The Botrytis pathogen commonly infects tissue through injuries and forms gray, velvety mats of sporulating tissues. Infected twigs may die back several inches. Infected blossoms often result in increased fruit drop and in injuries to the developing fruit. These fruit injuries are evident as ridges on mature fruit that result in a lower-graded crop during marketing. The name "gray mold" is used to describe the disease when it occurs as fruit decay during postharvest storage.
Comments on the Disease
Botrytis cinerea is a ubiquitous fungus that causes disease on twigs, leaves, blossoms, and fruit of citrus in areas with prolonged wet and cool conditions. Generally, the organism is a minor pathogen of citrus; lemons are infected more commonly than other citrus crops.
Management
General preventive measures, such as avoiding mechanical injury, protecting against frost and brown rot, and pruning regularly to improve air movement may help reduce the incidence of Botrytis diseases. Sprays of copper fungicides before rain or fog may help to reduce the blossom and fruit phases of the disease. Under prolonged cool, wet environmental conditions, frequent sprays are required and these may not be economical. Postharvest applications may be required in wet years to prevent fruit decay during storage and marketing.
| Common name | Amount to use | 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. | ||||
| PREHARVEST (BLOSSOM AND FRUIT INJURIES) | ||||
| A. | FIXED COPPER# | |||
| (various products) | Label rates | 24 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M1) | ||||
| COMMENTS: Where danger of copper injury is severe, apply in a mixture with 0.33 to 1 lb of hydrated lime per lb of dry copper fungicide. Not all copper compounds are approved for use in organic production; be sure to check individual products. | ||||
| POSTHARVEST (GRAY MOLD FRUIT DECAY) | ||||
| A. | FLUDIOXONIL/AZOXYSTROBIN | |||
| (Graduate A+) | 32–64 oz/100 gal water or 250,000 lb fruit | NA | NA | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12) and quinone outside inhibitor (11). | ||||
| COMMENTS: Use as a dip, drench, flood, or spray. | ||||
| B. | FLUDIOXONIL | |||
| (Graduate) | 16-32 oz | NA | NA | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12) | ||||
| COMMENTS: Use as a dip, drench, flood, or spray. See label for dilution rates. For maximum control, apply once before and once after storage; do not make more than two applications. | ||||
| C. | PYRIMETHANIL | |||
| (Penbotec 400SC) | Label rates | NA | NA | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Anilinopyrimidine (9) | ||||
| ‡ | 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. |
| # | Acceptable for use on organically grown produce. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. 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 fungicide with a different mode-of-action group number. |
| NA | Not applicable. |