The tomato plants in my greenhouse are now 1.5m tall and are producing tomatoes. Some of the leaves and branches are showing greyish patches and silvery mould like things on stems. What diseases they could be suffering from? Is there anything I can use to fix the problem?
It would appear from the photos you supplied that your tomatoes may well have Blight (rots the plant) or another type of fungal disease. Unfortunately it spreads quickly and it may already be too late to remedy the situation, but below are some suggestions.
Firstly, increase the ventilation in your greenhouse. If it is too humid, it can lead to various fungal infections and diseases. You may also be overwatering your tomato plants. Instead, water them deeply once every few days which is sufficient to maintain healthy, vigorous growth.
It is possible your soil may be poor draining or lacking in nutrients, or did you use the same soil from last season? It’s always preferable to start off with fresh soil in pots, and if growing in the ground, to prepare the soil well with Daltons Compost and garden mix before planting. You could try applying a copper oxychloride spray which helps prevent the spread of some fungal diseases. It’s a preventative at this stage, not a cure, due to the condition of the plants. Garden hygiene is also very important, clearing up at the end of the season and crop rotation will help to avoid blight spores.