Tomato and Potato Blight: Signs and What to Do
On this page
How to recognise it
It starts as a fast-spreading watery rot on the leaves that turns brown; a fine white growth can appear on the underside in damp weather, and stems blacken. Healthy-looking plants can be brown and collapsed within days.
Fruit and tubers
Tomato fruit develop a brown rot, and potato tubers show reddish-brown decay under the skin and can rot in store. Check stored potatoes and remove any that soften.
Why it arrives with the weather
Spores blow in on the wind and also arrive on infected plants and tubers; potatoes left in the ground carry it over to next year. Warm, wet spells give it its chance, and in the right weather a crop can go in about a week to ten days.
What to do when it hits
- Cut off and remove infected foliage as soon as you see it; if potato tops are badly hit, remove them so spores do not wash down to the tubers.
- Harvest tomatoes and potatoes you can still use.
- Bag the debris for council green waste or bury it deeply; do not put it on the home compost heap.
Next year
Dig up every leftover tuber so the disease has nowhere to overwinter, and consider blight-resistant potato varieties. Tomatoes under glass are less likely to be hit than outdoor plants. Growing guides: potatoes and tomatoes.
Related problems: blossom end rot, yellow leaves, powdery mildew. Or go back to all garden problems.
Blight questions
Can I eat blighted potatoes?
Tubers that look sound can be used; those with reddish-brown rot under the skin go off in store and should be thrown away.
Will it be in my soil next year?
It survives in infected tubers and plants rather than bare soil, so clear every leftover potato.
Are greenhouse tomatoes safe?
Safer, not immune: tomatoes under glass are less likely to be hit.
Regional notes
The problem is the same on both sides of the Atlantic; local advice and timing differ. Trusted local guides for this page:
- UK: RHS: Potato blight; RHS: Tomato blight; RHS: Grow your own: August jobs. Timing in your area: the UK vegetable planting calendar.
- USA: University of Wisconsin–Madison Extension: Late blight. Timing in your area: the USA vegetable planting calendar.
- Canada: your provincial agriculture department, or Canadian university gardening services. Timing in your area: the Canada vegetable planting calendar.
More problems: all garden problems.
Sources and further reading
- RHS: Potato blight
- RHS: Tomato blight
- University of Wisconsin–Madison Extension: Late blight
- RHS: Grow your own: August jobs
Facts on this page are summarised in our own words from the pages above; each is supported by at least two of them, or by one plus well-established growing science (noted in our research file). Every source was opened and checked on 23 October 2026.
Keep a garden record
Most problems come back to the same beds in the same weeks. A simple record of what grew where, and when trouble started, lets you get ahead of it next year. Sketch your beds in the free Vegetable Garden Layout Planner Tool, and keep sowing dates, problems and harvests in the Global Vegetable Garden Planner (printable PDF). Every crop we cover is in the vegetable growing guides.
Last reviewed:
Fix The Cause, Then Plan The Next Crop
Troubleshooting works best when you improve the growing conditions and record what changed for the next season.
Keep going
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.