Botrytis cinerea (Gray Mold)
Botrytis cinerea
0 host plants · Fungal
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Quick Reference
Management
Bloom period (primary risk) when flower petals provide the main entry point. Again near harvest when fruit is ripening. Extended wet periods in late spring through early summer. Cool, damp conditions in fall create a secondary window. In nursery and greenhouse settings, risk is year-round when humidity is poorly managed. source: PNW Plant Disease Management Handbook
4-6 hours continuous leaf wetness at 60-77°F (15-25°C); optimum 65-73°F (18-23°C). Shorter wetness durations sufficient at optimum temperature. Rain, overhead irrigation, heavy dew, and fog all provide sufficient moisture. RH >90% supports spore germination even without free water. Dense canopy, tight fruit clusters, and high plant density trap moisture and favor infection. source: PNW Plant Disease Management Handbook
Cultural Controls
- Prune annually to remove infected twigs and dead wood, and to open canopy for air circulation. PNW Plant Disease Management Handbook
- Space plants to maximize air circulation and promote rapid drying of foliage and fruit. PNW Plant Disease Management Handbook
- Use drip irrigation or schedule overhead irrigation to allow foliage and fruit to dry quickly. If overhead irrigation is necessary, limit to morning hours so foliage dries during the day. PNW Plant Disease Management Handbook
- Avoid late-season high-nitrogen fertilization that promotes soft, winter-susceptible growth and dense canopy. PNW Plant Disease Management Handbook
- Maintain weed control to improve air flow at the plant base. PNW Plant Disease Management Handbook
- Harvest fruit at proper maturity and move to cold storage promptly to minimize post-harvest rot. PNW Plant Disease Management Handbook
Gray mold is the most reliable fungal disease on soft fruit and ornamental flowers in the Puget Sound lowlands. March through June delivers 50-70°F temperatures with persistent rain, fog, and slow-drying conditions that routinely exceed the 4-6 hour leaf wetness threshold for infection. Unlike warmer regions where summer heat suppresses the pathogen by mid-June, suppression here does not arrive reliably until July. Fall rains in September create a second activity window. WSU research documents widespread fungicide resistance (70% of WA fields by 2014), making cultural controls the primary management strategy. The UK (RHS), with an analogous maritime climate, manages without any approved home-garden fungicides.
Sources & References
Primary: PNW Plant Disease Management Handbook
- PNW Plant Disease Management Handbook - Blueberry
- PNW Plant Disease Management Handbook - Rose
- PNW Plant Disease Management Handbook - Grape
- PNW Plant Disease Management Handbook - Rhododendron Petal Blight
- PNW Plant Disease Management Handbook - Rhododendron Shoot Blight
- PNW Plant Disease Management Handbook - Raspberry
- PNW Plant Disease Management Handbook - Douglas-fir
- PNW Plant Disease Management Handbook - Strawberry