Botrytis — grey mould — is one of the most common and damaging plant diseases, especially in cool, damp, still conditions. It rots soft tissue, spoils flowers and fruit, and spreads fast on dead and dying plant material. This guide covers the core disease (Botrytis cinerea / grey mould); the right response varies by plant and situation, and not every “blossom blight” is Botrytis (see the note below).
What Botrytis is
Botrytis (mostly Botrytis cinerea) is a fungus that attacks soft or damaged plant tissue and thrives in high humidity, poor airflow and cool temperatures. It feeds readily on dead and dying material and then moves into healthy soft tissue, which is why hygiene and airflow matter so much.
Typical symptoms
- Grey, fuzzy mould: the classic sign — a soft, dusty grey coating on affected tissue that puffs into spores when disturbed.
- Leaf & stem symptoms: water-soaked or browning patches that turn soft and become covered in grey fuzz; stems can rot and collapse.
- Soft tissue rot: soft leaves, flowers and fruit rot rapidly; whole shoots may wilt from a rotted base.
Botrytis on flowers and developing fruit
This branch matters for anyone wondering why a plant flowers but doesn’t fruit. Botrytis frequently infects flowers, buds and developing fruit:
- Blossom infection / flower blight: petals and buds turn brown, rot and become covered in grey mould — flowers are lost before they can set.
- Fruit infection / fruit rot: young and ripening fruit rot (grey mould on strawberries, grapes, soft fruit and many others), and infection can enter through the old flower parts still attached to the young fruit.
- Result: poor fruit set and young-fruit loss on susceptible plants — so on those plants, this is a disease cause of “no fruit,” not a pollination one.
Conditions that favour it
- High humidity and prolonged leaf/flower wetness.
- Poor airflow and still, damp air.
- Dense growth and overcrowding.
- Dead plant material — spent flowers, fallen leaves, damaged tissue — which it colonises first.
Sanitation
The single most important control: remove dead and dying material promptly — spent flowers, fallen leaves, prunings and any infected tissue — because Botrytis builds up on them and spreads to healthy growth. Bin infected material; don’t leave it lying or heavily compost it. Clean tools between plants.
Ventilation & watering practices
- Improve airflow: space plants, thin dense growth, and ventilate greenhouses and indoor spaces to cut humidity.
- Water at the base, early in the day, so foliage and flowers dry quickly; avoid wetting flowers and soft growth late in the day.
Removing affected material
Cut out infected parts well back into healthy tissue with clean, sterilised tools, and remove them from the area. Handle gently and preferably when dry — disturbing mouldy tissue releases clouds of spores.
Treatment principles
- Fix the conditions first (airflow, humidity, sanitation) — chemical control rarely holds if the environment still favours the fungus.
- Low-toxicity and biological options exist; if a fungicide is warranted, choose one labelled for Botrytis on your plant and follow its label exactly. No single fungicide suits every plant, resistance is a known issue, and rates must not be exceeded.
Prevention
- Space and prune for airflow; avoid overcrowding.
- Remove spent flowers, fallen leaves and debris routinely.
- Water at the base, early; keep humidity down.
- Avoid injuring plants (wounds are entry points) and don’t leave dying material on or around plants.
Greenhouse & indoor considerations
Enclosed, humid, still environments are prime Botrytis territory. Ventilate actively, avoid overcrowding on benches, keep humidity down (especially at night), promptly remove any affected plants or tissue, and avoid leaving water sitting on foliage.
Important: not all blossom blight is Botrytis
Grey fuzzy mould in damp conditions points to Botrytis, but other diseases can also blight blossoms and rot fruit (for example, certain Monilinia blossom/brown-rot diseases on some fruit trees, and various bacterial and fungal blights). Don’t assume every flower or fruit rot is Botrytis — identify the disease (grey fuzzy sporulation is the Botrytis signature) before choosing a response, and check plant-specific guidance.
Quick questions
What does Botrytis look like? A soft, fuzzy grey mould on rotting leaves, stems, flowers or fruit that releases a puff of spores when touched.
Why do my flowers/fruit rot before ripening? Often Botrytis in damp, still, crowded conditions — improve airflow, remove affected parts and spent flowers, and water at the base.
Is every flower rot Botrytis? No — other blossom-blight diseases exist; identify by the grey fuzzy mould and check plant-specific guidance before treating.
Related guides
- All plant pests & protection
- Powdery mildew · spider mites · mealybugs
- Thrips on plants · why plants flower but don’t fruit
- Choosing a plant sprayer for applying treatments · all plant pests & protection
- anthracnose
- leaf spot
