Prevent moulds and fungal disease
This warm weather has been a boon for some plants but warm, wet weather can cause high humidity and encourage fungal infections and fuzzy moulds. The most common cause of mildew is moisture above ground and dry roots below. This may seem a laughable possibility this year considering how wet the weather has been but moisture needs to get to the roots of the plants not just wet the leaves. Even heavy rain won't reach plant roots if the plants are in a rain shadow or planted too close together.
Warm, moist air encourages fungus and fungal spores are easily spread by rain splash from plant to plant. So our recent wet weather is likely to have increased plant problems. Good air circulation is also vital, closed atmospheres make the problem worse.
In the greenhouse ‘damping off' is a particularly frustrating fungal infection, whole trays of seemingly healthy seedlings can simply keel over. Avoid this disease by practicing scrupulous hygiene and careful watering; keep compost just moist but not wet and always use clean tap water for watering; never water seedlings with water from a water butt, the risk of infection is too great. Pick up debris such as fallen flowers and leaves from the greenhouse staging and from the soil around overwintering plants as soon as you see it. Plant debris can be a major cause of grey mould (botrytis).
Spray vulnerable plants with a systemic fungicide but follow the directions on the packets and never spray in bright sunlight. Some plants may not be suitable for spraying because their leaves can scorch. Keep a watchful eye out for signs of disease on stems and foliage and act fast to prevent it spreading. Prevention is always better than cure!
My young violas were grown from seed and they looked healthy enough, but at the weekend I noticed some spots on the leaves.
This may be the start of a mildew infection so these viola plants are going into quarantine! I'll spray with fungicide and take off the offending leaves until the cause of those spots is confirmed.
Pansies and violas can be attacked by leaf spot diseases as well as mildew so these spots may be symptoms of disease as well as fungal infections. If it's a disease, spots can get darker or lighter depending on which leaf spot disease is responsible. Grey fuzzy mould may also appear on the undersides of the leaves in areas that correspond to the spots on the upper surface of the leaves. Unlike powdery and downy mildew which are spread by rain splash, diseases spread from plant to plant so pick off and discard infected leaves as quickly as possible to stop disease from spreading.