Tomato leaf mould
A fungal disease of tomatoes in humid greenhouses and polytunnels that causes pale spots on top of leaves and olive-green velvety mould underneath.
Also known as: Passalora leaf mould, Cladosporium leaf mould
Symptoms and identification
Pale green to yellow spots appear on the upper leaf surface, and olive-green to brown velvety mould grows on the underside beneath them. Leaves curl, wither and drop, starting with the older, lower leaves, and fruit yield is reduced.
Causes
The fungus needs high humidity, above about 85 per cent, and moderate temperatures. It spreads by airborne spores in crowded, poorly ventilated greenhouses, and survives on debris and on structures.
Organic treatment
Remove affected leaves and bin them, and lower humidity by venting and spacing. Copper or sulphur-based sprays may help protect healthy leaves.
Prevention
Ventilate greenhouses well, space and prune plants for airflow, water at the base in the morning and avoid wetting leaves. Choose resistant varieties and clean up debris at the end of the season.
Chemical treatment (use with care)
Use a fungicide labelled for tomato leaf mould, following the label, but improving ventilation is the most effective step.