Botrytis (grey mould)
Also known as Grey mould, Gray mold, Botrytis cinerea
In short
Botrytis cinerea is a very common fungus that grows on dead and dying plant material and can then invade living tissue, especially flowers, fruit, soft growth and wounds. It is favoured by mild, humid, stagnant conditions and crowded plants. Good hygiene and air movement are the main defences.
How it looks
A fuzzy, grey to grey-brown, velvety mould on rotting flowers, leaves, stems or fruit; the name cinerea refers to the ash-grey colour of the spore masses. When disturbed, it releases a puff of dusty spores. Affected tissue first looks water-soaked or brown, then collapses. Small, hard, black seed-like bodies (sclerotia) may form in dead tissue.
Signs
Brown spots or blotches on petals and leaves, soft brown rot of buds, fruit and stems, dieback of shoots from infected points, and whole flowers or leaves shrivelling and dying under a grey furry coating.
Life cycle
The fungus grows on dead organic material and produces airborne spores spread by air currents and water splash. It usually enters living plants through wounds or ageing, dying tissue, but on flowers and fruit it can infect without wounds when humidity is high. Sclerotia in dead tissue and soil let it survive for long periods and produce new spores later. Several infection cycles can occur in one season.
What favours it
High humidity, moist leaf surfaces, poor ventilation and overcrowding; mild temperatures around 18–24 °C are especially favourable. Dead leaves and spent flowers left on plants or the pot surface give it a foothold.
Prevention
- Remove dead leaves, spent flowers and fallen debris promptly, including from the pot surface.
- Space plants and ventilate so air moves around them; avoid crowding in propagators and cabinets.
- Water so foliage and flowers stay dry and avoid leaving water sitting on leaves overnight.
- Avoid wounding stems and leaves, and handle cut flowers and fruit carefully.
Treatment
Start with the first step and move down only if the problem persists.
- Carefully bag infected parts before removing them, so spores are not shaken over other plants.
- Cut out affected tissue back to healthy growth with clean tools.
- Lower humidity and increase air movement.
- Some countries (for example the UK) have no fungicides approved for gardeners against grey mould; where products exist, follow the product label.
Pros and cons
Cons
- Very wide host range, so an outbreak can move between unrelated plants.
- Can destroy flowers, buds, seedlings and fruit quickly in humid conditions.
Look-alikes
- Bacterial soft rot
- Bacterial soft rot is slimy and often foul-smelling, without dusty grey spores.
- Damping off
- Damping off collapses seedlings at soil level and may show white rather than grey growth; botrytis can be one of its causes.
- Powdery mildew
- Powdery mildew is a flat white dust on living leaves; botrytis is a raised grey fur on rotting tissue.
Affected plants
More than 200 plant species; economically important on grapes, strawberries and other soft fruit and on bulb crops, and common on flowers, soft growth and seedlings of ornamental and indoor plants.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.