Tomato leaf mould: how to recognise and treat it

Disease

Symptoms

Pale green to yellow blotches on the upper surface of the lower leaves first, with a velvety grey-brown to olive-green mould on the underside below each blotch.
Heavily infected leaves turn brown and shrivel but stay on the plant; affected plants lack vigour and yield poorly.
Occasionally flowers and fruit are attacked — fruit may get a black, leathery rot at the stem end.

Pick off infected leaves as soon as you see them.
Trim off some lower leaves once the fruit has set to let air move around the plants.
Where copper fungicides are approved for home use, spray them as a preventive programme before the disease spreads; follow the label.

Where approved for home gardens (e.g. in the US), a preventive programme of chlorothalonil; in the UK no fungicides are available to gardeners for leaf mould. Follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Grow resistant cultivars (e.g. 'Shirley', 'Cumulus'); new races of the fungus can overcome the resistance.
Ventilate the greenhouse well, keep humidity below about 85% and avoid temperatures above 21 °C.
Water the soil, not the leaves, especially in the evening; do not let the soil dry out; space and stake plants for airflow.
At the end of the season remove all plants and debris, clean the greenhouse structure, and rotate with crops other than tomatoes.

Figures checked against these sources.