What is grey mould?

Grey mould is a disease caused by the fungus Botrytis cinerea. It normally enters through a wound or infects plants under stress, but will infect healthy plants as well, especially under humid conditions.

Cyclamen grown under glass are commonly affected, but B. cinerea affects a wide range of other plants, both outdoors and under protection. Attacks can be expected at all times of year.

Symptoms

You may see the following symptoms:

• On flowers: Small discoloured spots appear. If conditions are sufficiently humid these spread rapidly and cause the flowers to go brown and shrivel
• On leaf and flower stalks: The fungus causes the stalks of developing leaves and flowers to collapse
• On all infected parts: Under humid conditions the fungus grows out from the dead tissues to produce a grey-brown, fuzzy mould. Black seed-like structures can form in dead tissues (these are often overlooked)

Control

Non-chemical control

• Maintain good hygiene and do not allow dead plant material to accumulate either on plants in the greenhouse or as rubbish. Remove dead leaves and flowers promptly and destroy
• Maintain good air circulation and do not overcrowd plants

Chemical control

There are no chemical controls available to gardeners for use against grey mould.

Biology

Botrytis cinerea is found very commonly as a saprophyte (a micro-organism living on dead organic material), producing large quantities of airborne spores under humid conditions. These spores can infect living plant tissues under certain circumstances. Healthy green tissues are usually only infected through wounds. Some more delicate tissues, such as flowers and ripening fruit, may be attacked even though they are not wounded. Very humid conditions favour both the initial infection and the subsequent spread through the tissues.

The fungus forms black seed-like resting structures (sclerotia) in dead tissues. These can remain in a dormant state for some time, but eventually germinate to produce more spores.