Grey mould (Botryotinia fuckeliana / Botrytis cinerea) is a commonly found fungus in many environments. It survives in plant parts like bulbs and crop residues or as sclerotia (drought- and cold-resistant structures) in the soil.
Life cycle and appearance of Grey mould
Spores of grey mould (Botryotinia fuckeliana / Botrytis cinerea) need moisture (dew, rain, irrigation water) and nutrients for germination. Germination also happens at very high relative humidity (RH > 93%) on dry plants. The germ tube grows into the plant. Grey mould (Botryotinia fuckeliana / Botrytis cinerea) is a necrotrophic fungus, meaning that it excretes compounds that kill the plant cells and then uses the content of the plant cells as nutrients. On the infected area, new spores are formed within a few days. Under circumstances unfavourable for germination, the spores can survive a few days on the plant surface and still germinate when the RH increases, for example when cut flowers are harvested and put into cold storage.
Wounds can also provide the fungus with sufficient moisture, for example pruning wounds on the stems of cucumber and tomato.
In general, grey mould (Botryotinia fuckeliana / Botrytis cinerea) is considered a weak pathogen, only infecting weakened or damaged plants.
As the name suggests, grey mould’s (Botryotinia fuckeliana / Botrytis cinerea) most common symptoms are grey-brown lesions. The lesions occur on leaves, stems, fruits and flowers. On flowers, usually small round specks occur first, called ‘pocks’. These may or may not grow into larger grey-brown lesions. The symptoms on fruits, flowers and on various parts of potted plants often only become visible during and after cold storage. In lettuce, grey mould (Botryotinia fuckeliana / Botrytis cinerea)is part of the foot rot complex, which causes rotting of the foot and may cause death of the plants. In cucumber and tomato the fungus causes lesions on pruning wounds. These lesions may encircle the stem, so the part of the plant above the lesion wilts and dies.
In vegetables and strawberry, grey mould (Botryotinia fuckeliana / Botrytis cinerea)affects the fruit. In potted plants, the cuttings die due to carry-over infection from infected parent plants.
How to prevent Grey mould
- Make sure the crop grows regularly with not too much vegetative growth, in order to maintain a microclimate which is not humid enough for grey mould
- Provide sufficient ventilation in greenhouse crops
- Remove diseased plants or plant parts in a closed plastic bag
- In tomato: prune with a knife and not by hand, to avoid rugged, irregular wound surfaces
- In cucumber:
- remove dead leaves on the stem once, especially in the autumn, because from these leaves the stems are infected, possibly killing the entire plant
- maintain a higher RH once stem infection is present, since more plants die at lower RH
- remove aborting fruits, since these can be infected after abortion and then provide a large amount of inoculum
- Extra Silicon and/or Calcium nutrition hardens the cell walls and makes it harder for the fungi to enter the leaves
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