Q What is grey mould?

A Grey mould is a fungus, Botrytis cinerea. Its spores are around us all of the time, and it lives on both living and dead plant material.

Caption: Remove anything that has been affected by grey mould to help avoid it spreading

Q Which plants are most likely to be affected by grey mould?

A Plants that have been stressed or injured in some way are liable to be attacked by grey mould. Infections may also arise where diseased tissue comes into contact with healthy tissue. The disease affects ornamentals, fruit and vegetables, as well as greenhouse plants.

Q What conditions favour grey-mould attack?

A The fungus thrives during cool, wet periods when humidity is high and temperatures are low.

Q What symptoms of grey mould should I look out for?

A A grey-brown or off-white fuzzy growth on the leaves, stems, fruits, buds or flowers of plants is the first thing you are likely to notice. Often when the plant is touched, a cloud of spores will be released into the air. Other symptoms of this disease include petal-spotting, wilting, shrivelling, rotting tissue and dieback. If grey mould infects lettuces during the hearting-up phase, a reddish-brown soft rot occurs that can destroy the stem tissues at ground level in less than 72 hours. Bacteria then invade the damaged tissues, producing a yellowish-brown slime. Stem damage on tomatoes may lead to rotting of the stems and fruit. Symptoms on tomato fruits may also show as ghost spots (yellow circles).

Caption: Grey mould causes plants to rot

Q How does the grey-mould fungus survive in winter?

A During the winter, numerous small, raised, black sclerotia (resting bodies) may be seen on plant debris. These are around 3-5mm long and are capable of surviving long periods of harsh weather. They remain dormant until conditions are favourable.

Q How do outdoor fruits become infected with grey mould?

A Early in the summer, grey mould enters the flowers as they fade and remains dormant in the fruits until they begin to ripen, when the grey, fuzzy, spore-producing structures develop. Grey mould can also colonise the straw that is used to mulch strawberries.

On raspberry canes and gooseberries, the leaves on infected stems turn yellow, grey or white, especially at the edges. Then they’ll wither, and sometimes fall. Grapes with grey mould may be infected and rot, following berry split caused by mildew or irregular watering.

Q How can I reduce the chances of grey mould attacking my plants?

A If cool, damp conditions prevail, keep a look-out for early signs of attack. Keep your plants growing well throughout the year, try to avoid physical damage and deadhead regularly. Grey mould will attack any plant that has been injured, so remove dead or injured plant parts before they can become infected.

If plants have been attacked, remove the infected areas as soon as possible, cutting back into healthy growth. Clear away plant debris and keep the weeds down.

Q How can I prevent grey-mould attacks in the greenhouse?

A Keep a close eye on the greenhouse, where grey mould can run riot if given a chance. Good ventilation is essential, even during the winter. Plants should be spaced far enough apart to allow normal air circulation. Adequate drainage of the compost or border soil is also important. When you water plants, avoid wetting the leaves or stems, and in autumn, water only in the morning. Avoid damaging the stems and leaves, particularly of seedlings, when pricking out or potting up.

Remove dead and dying leaves, flowers and fruit as soon as possible and keep weeds below greenhouse staging under control. If damping down of the greenhouse is necessary, allow time for the water to evaporate before temperatures drop at night.

Caption: Removing dead plant material will help prevent grey mould

Q Can I spray against grey mould if the infection keeps recurring?

A There is no chemical control for this problem available for gardeners to use.