Home Garden problems, pests, diseases Grey mould

Grey mould

Surviving Botrytis attacks

Grey mould
Grey mould on a cut-back geranium in a humid environment under glass

In a damp summer, it’s inevitable that grey mould will raise its ugly head.

It is caused by the fungus Botrytis cinerea and infects many plants, especially those grown under glass where conditions are humid.

Grey mould normally enters through a wound or infects plants under stress, but healthy plants are at risk in humid conditions – no time of the year is ‘safe’ from it.

Apples, grapes, strawberries, blackberries, raspberries, gooseberries, beans, curcubits, lettuce, tomatoes, Chrysanthemum, Cyclamen, Pelargonium (geranium), and Primula are particularly at risk.

Unlike powdery mildew, which has a very specific host, Botrytis has a very wide range, but there are closely-related species which are much more specific, including those infecting snowdrops, peonies and broad beans.

Grey mould symptoms

  • Under humid conditions, fuzzy grey mould grows on buds, leaves, flowers or fruit.
  • Buds and flowers shrivel and die.
  • Small black seed-like structures form in the infected material.
  • On soft fruit, particularly gooseberries, Botrytis infection kills branches, but the fuzzy mould is seldom seen.
  • On strawberries and grapes, infection leads to a soft brown rot, often as the fruit is ripening.

Organic control

Grey mould
Grey mould on a sweet pea flower
  • Hygiene is vital, especially under glass. Remove dead and dying leaves, buds and flowers immediately.
  • Don’t leave dead plant material lying around.
  • Improve ventilation in glasshouses.
  • Do not overcrowd plants, either under glass or in beds.
  • In torrential rain where flowers are soaked, especially seen in Pelargonium flowers, remove them as soon as possible.