Plant Problem Diagnostic
Botrytis Blight / Gray Mold (Botrytis cinerea): Identification and Cultural Management
The short answer
Botrytis blight, or gray mold, is a fungal disease caused by Botrytis cinerea that attacks a huge range of plants, especially soft tissues like flowers, ripening fruit, and tender or dying leaves. The signature sign is a fuzzy gray to tan mold on blighted tissue. It causes browning of flower petals, soft rot of fruit, and irregular brown leaf lesions that sometimes show a target-like banding, and it readily colonizes wounded, aging, or dead plant parts before spreading to healthy ones.
The fungus thrives in cool, damp, crowded conditions with poor air movement, and its spores germinate when tissue stays wet for several hours. The most effective home and greenhouse controls are cultural: improve air circulation, lower humidity, avoid wetting foliage and flowers, and promptly remove faded blooms, fallen petals, and dead or infected tissue. If the disease persists in an enclosed space, a fungicide labeled for gray mold can supplement sanitation following the label.
How to identify it
- Fuzzy gray to tan mold on blighted flowers, fruit, or leaves
- Brown spots on flower petals that enlarge and kill the bloom, sometimes preventing buds from opening
- Irregular necrotic leaf areas, occasionally with a bull's-eye or banded pattern
- Soft rot on ripening or stored fruit and stem cankers on some hosts
Conditions that favor it
- Cool temperatures with high relative humidity
- Leaves, flowers, or fruit that stay wet for several hours
- Crowded plantings with poor air movement
- Abundant wounded, aging, or dead plant tissue for the fungus to colonize first
Cultural management steps
- 1Improve airflow and lower humidity — Space plants, prune for circulation, and in a greenhouse vent and manage humidity so tissue dries quickly.
- 2Keep foliage and flowers dry — Water at the base and avoid overhead irrigation late in the day so surfaces don't stay wet overnight.
- 3Remove infected and spent tissue — Promptly pick off faded flowers, fallen petals, and dead or diseased leaves and dispose of them; do not leave debris on the soil.
- 4Handle plants gently — Minimize wounds and avoid working with plants when they are wet, since the fungus enters wounds and spreads on wet tissue.
When to escalate
If gray mold keeps returning in a greenhouse or on high-value plantings despite good sanitation and humidity control, or if you are unsure of the diagnosis, consult your local Extension. Any fungicide should be labeled for gray mold on that plant and applied per the label; rotating chemistries is often advised because Botrytis can develop resistance.
⚠ Botrytis spreads fastest through crowded, humid, wet plantings full of dead tissue. Sanitation and drying the environment matter more than any single spray.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Wisconsin-Madison Extension — Gray Mold (Botrytis Blight) — Gray fuzzy mold, petal browning, bull's-eye leaf lesions, favored by cool high humidity and wet tissue; airflow and sanitation controls
- Penn State Extension — Managing Botrytis or Gray Mold in the Greenhouse — Air movement, humidity management, and removal of blighted tissue are critical to prevention
- University of Minnesota Extension — Gray mold of tomatoes — Botrytis colonizes wounded and dying tissue and spreads to healthy parts; managed by sanitation and reducing humidity