One of the biggest killers in the greenhouse at this time of year is grey mould, also known as botrytis. More accurately known as Botrytis cinerea, this ubiquitous fungal disease is actually quite interesting – well the etymology is. Botrys is the Greek word for grapes and it means disease. So this is a grape disease. It is most interesting for being the cause of ‘noble rot’ in grapes at the end of the growing season and affected grapes are very high in sugar and lower in moisture and are used to make sweet wines such as Sauternes. Cinerea means grey or ash-coloured and refers to the colour of the spores that cover affected plant material.
So although this disease is associated with grapes it is not a fussy fungus and it attacks all dying plant material in cold, damp conditions.
So, in winter, it is very important to remove any dead leaves and petals and cut back stems to a bud so there are no dead areas on the plants or the disease can rapidly spread into living tissues and, all too quickly kill plants such as pelargoniums and, as seen above, abutilons. Pick up fallen leaves and try to avoid splashing water around. Keep leaves dry where possible to avoid increasing humidity.
There are no suitable fungicides to control the disease and, in any case, spraying more water around would only make the problem worse. Grey mould also affects fruits and flowers in wet weather in summer, particularly strawberries.