Gray mold (Botrytis blight) identification & organic treatment
Botrytis cinerea
How to identify gray mold (botrytis blight)
An opportunistic fungus that colonizes dead or dying tissue (old flower petals, bruised fruit, wounds) and then spreads into healthy tissue, producing a fuzzy gray-brown mold coat.
Symptoms
- Fuzzy gray-brown mold on flowers, stems, and fruit, especially where a spent bloom or wound is present
- Water-soaked, tan-brown lesions that spread into stems, sometimes girdling them ('ghost spot' pale rings on tomato fruit)
- Soft, watery rot on ripe fruit in storage or in humid, crowded plantings
Host crops
Tomato, Strawberry, Grape, Pepper, Lettuce, Bush bean.
How it spreads
Airborne spores land on any dead or damaged tissue (old petals, pruning wounds, bruises) and colonize from there into healthy parts; spreads fastest in stagnant, humid air.
Favorable conditions
Cool-to-mild temps (60-75°F) with high humidity or condensation; classic greenhouse and high-tunnel problem, also common in a rainy, crowded outdoor bed.
Progression
- Colonizes dead tissue (Any time flowers/leaves senesce) — Fuzzy gray growth on spent blossoms and old leaves.
- Invades living tissue (Days after, in humid air) — Stem lesions and fruit rot spread from the contact point.
- Sporulation (Ongoing in humidity) — Gray spore dust puffs when touched, seeding new infections.
Organic treatment for gray mold (botrytis blight)
- 1. Remove spent blooms and infected tissue · low effort
Pinch off dead petals and any moldy leaf/stem/fruit and discard away from the garden.
When: 2x weekly
- 2. Increase ventilation · low effort
Prune for airflow, widen spacing, and vent greenhouses/tunnels; run a fan in enclosed structures.
When: Ongoing, especially humid stretches
- 3. Copper or Bacillus subtilis biofungicide · medium effort
Apply an OMRI-listed copper or Bacillus subtilis product on a 7-10 day schedule during high-risk (cool, damp) periods.
When: Preventive, high humidity season
Prevention
- Avoid overhead watering and watering late in the day.
- Don't crowd plants; prune lower leaves for airflow.
- Harvest ripe fruit promptly and handle without bruising.
- Clean up plant debris; the fungus survives readily on dead tissue.
Easy to confuse with
- Sclerotinia white mold (Botrytis is gray/brown fuzz, not white cottony with black sclerotia)
- Bacterial soft rot (slimy, foul odor vs. fuzzy mold)
Terms on this page
- Sclerotia
- Hard, seed-like resting bodies a fungus forms to survive winter and dry spells in the soil. They look like tan, brown or black BBs or mustard seeds.
- Spores / sporulation
- Spores are a pathogen's seeds. Sporulation is when it starts producing them, often as fuzz or powder you can see.
Sources
New to a word on this page? See the plain-English glossary.