Gray Mould (Botrytis blight)

This common fungus infects leaves, rhizomes, stems, flowers, and seedlings of many plants. The disease thrives on mild, moist conditions and often survives on infected plant debris. The fungus which causes the disease is Botrytis cinerea and it is known to infect large numbers of differing plant species, but is a serious problem in only a small number of them.

Botrytis blight can be a problem in greenhouses where the humidity is high and the temperature moderate. It attacks tomatoes, as well as cucumbers and other fleshy plants, and fruits such as strawberries and raspberries.

Botrytis blight can affect plants in various of ways. It may cause collapse of seedlings, blossom blight, fruit rot, stem and crown rot, or shoot blight. The first symptom is usually the appearance of water-soaked lesions. This is followed by tissues becoming soft and watery. The affected parts of the plant then wilt and collapse.

If the humidity remains high, the infected area quickly becomes covered with a gray-brown mass of fungus and spores. Lots of spores are produced and these are easily blown or splashed onto healthy foliage. If there is moisture present and other conditions are favorable, germination and infection can take place in as little as a few hours.

Varying in size up to 1/4 inch, flattened, black, Sclerotia may be produced on fleshy parts of stems and fruits. These structures allow the fungus to survive when conditions are not favorable for growth. The Sclerotia are not always easy to see as they may be embedded in decayed tissue or coated with soil and other debris.

The spores need a film of moisture in order to germinate and infect plants. This is why gray mold thrives in humid and moderate conditions. In greenhouses, good ventilation will help to control gray mold. The use of a small fan to improve air circulation will also help to keep this problem at bay.

The fungus thrives on plant debris and detritus, so cleanliness and sanitation is an essential part of gray mold control. Fallen leaves and dead plants, as well as any extraneous plant material, should be removed from the greenhouse and burned. This will greatly reduce the amount of infectious material available, and so limit the fungal spread.

In the event of a bad outbreak of Gray Mould it may be necessary to resort to some form of chemical treatment. There are a lot of suitable fungicides available through your local garden center, so ask for advice as to the best one for the particular crop you are growing.