Potato and Tomato Blight
Disease · Commonly affects: potatoes, tomatoes, outdoor tomatoes, greenhouse tomatoes, aubergines, pepper plants
Potato and tomato blight is a fast-moving disease caused by Phytophthora infestans. It is especially troublesome during warm, wet UK summers, when rain and humid air allow spores to spread quickly between plants. Left unchecked, it can strip foliage and spoil both potato tubers and tomato fruit within a short time.
How to identify it
Look for irregular brown or olive-brown patches, often 5-20 mm across at first, on leaves and dark brown streaks on stems. In humid weather, a fine white mouldy growth may appear on the underside of leaf patches, particularly around their edges. Potato foliage can rapidly blacken and collapse. Tomatoes develop firm, brown, uneven patches on fruit; potato tubers may show brown, slightly sunken skin and rusty-brown flesh beneath.
Damage
Blight reduces the leaf area needed to feed developing crops, so potato yields fall and tubers remain small. In severe outbreaks, whole plants die back quickly. Spores can wash from foliage into the soil and infect tubers. Tomato fruit becomes inedible, and affected potatoes may rot in storage, spreading decay to neighbouring tubers.
Prevention
Choose blight-resistant potato and tomato varieties where possible, and buy healthy seed potatoes. Give plants generous spacing so leaves dry after rain, and earth up potatoes well to keep tubers covered. Rotate potatoes and tomatoes away from the same ground for several years. Grow tomatoes under cover with good ventilation, keeping rain off foliage. Clear volunteers and self-sown plants, and remove old crop debris promptly.
How to manage it
Check plants often during humid, unsettled weather. At the first clear signs, remove affected leaves and stems carefully, avoiding unnecessary handling of wet plants. Lift potato crops once foliage is badly affected and discard visibly diseased tubers. Bin affected foliage, fruit and tubers rather than composting them. Harvest only dry, sound potatoes for storage, and inspect stored crops regularly, removing any that soften or rot.
Potato and Tomato Blight: frequently asked questions
How do I identify potato and tomato blight?
Look for irregular brown or olive-brown patches, often 5-20 mm across at first, on leaves and dark brown streaks on stems.
How do I prevent potato and tomato blight?
Choose blight-resistant potato and tomato varieties where possible, and buy healthy seed potatoes.
How do I get rid of potato and tomato blight?
Check plants often during humid, unsettled weather.
General guidance for UK home gardens and allotments, focused on prevention and non-chemical control. For a confirmed diagnosis, the RHS or a local garden centre can help. Page updated 19 Sep 2026.