Grey mould is a common fungal disease that can affect many plants; however it can become quite a serious problem on tomato plants especially if they are grown under protected conditions environment such as those provide by a greenhouse. Once established in a protected environment, grey mould can be difficult to bring under control and it may in fact remain present within the environment all year round. If left uncontrolled, grey mould will eventually kill off the plants.
Cause: Initial contamination is usually from wind carried fungal spores which infect the host tomato plant through a point of damage such as insect damage, decaying plant tissue or pruning wounds. Grey mould prefers cool and humid conditions. Unfortunately these conditions will also stress the tomato plants, making them further susceptible to the disease.
Symptoms: The most characteristic symptom of a grey mould infection is a grey-brown furry mould, usually first noticed on shrivelled buds and flowers. The infection can spread rapidly – especially under damp/humid conditions and when shaken, clouds of spores are released from these infected areas. The infected areas can expand rapidly covering whole stems, leaves or petals. If left to their own devices these stem infections can ‘ring’ the whole stem and cause the plants above the infected area to wilt and die. More importantly, fungus growing on infected petals may transfer onto the fruit, leaving it inedible.
Treatment: Control of Grey Mould is all about maintaining healthy growing conditions and that means a dry, well ventilated environment. To begin with you will need to reduce the risk of spreading the disease on to other plants and so to start with, increase ventilation as best as you can and only water the plants in the mornings, and as you do so, try to stop water from touching the foliage. This will reduce humidity through the day slowing the spread and growth of new spores. Prune lower, lateral stems regularly and remove any old or dense foliage leaves as this will also improve air movement through the plants. Spray with a sulphur based fungicide for chemical control which may need to be re-applied every 7 days. However if the growing conditions are not suitably improved the infection will inevitably return.
For an organic cultural control of ‘Grey Mould’ take the following steps:
2. Remove all plant debris from the previous crop – as this is an obvious carrier for dormant 'Grey mould’ spores that can infect the following crop. This debris should be either burned or disposed of well away from other similar crops.
3. Cover the ground below your tomatoes with either plastic sheeting or some other non-porous substitute. This will act as an effective barrier for re-infection by preventing the grey mould fungal spores from surviving in the soil and become a source of infection for the next crop.
4. If you are growing your tomatoes under protection, such as a greenhouse, wash down the walls and floors after each crop.
5. Make sure that you have adequate ventilation. If you do not, consider using fans to help move air within the greenhouse.
6. Reduce your planting density and remove the older, lower leaves from the tomato plants once the first fruits have started to swell as this will allow good air movement between the plants preventing the high humidity needed for infection.
7. Try to avoid wetting the main bulk of the plant when watering and certainly never spray your crops in the afternoon or at any time when the weather is such that the plants will be unable to properly dry out.