Tomato Blight UK: Identify, Treat and Prevent It
Key Takeaways
- Tomato blight hits UK gardens in warm, wet summers and can wipe out a whole crop within days. August is peak season, so check plants daily once the weather turns humid.
- Prevention beats treatment every time. Grow blight-resistant varieties like Suttons Tomato Seeds F1 Crimson Crush or Suttons Tomato Seeds Crimson Cherry F1, and you can largely avoid the disease altogether.
- Water at the base, never overhead. Wet leaves are how blight spores get a foothold, so aim a Hozelock Superhoze Expanding Hose at the soil, not the foliage.
- Act fast at the first sign. Remove and destroy infected foliage immediately, and apply a preventive spray like Westland Fungus Guard Fungicide Spray or Liquid Copper Fungicide to healthy plants.
- There is no cure once blight takes hold. Your job is identification, removal, and protecting everything nearby - then plan resistant varieties for next year.
Suggested Reading: See our growing tomatoes in pots guide and red spider mite control guide for more tomato care.
You walk out to the greenhouse on a warm August morning and the leaves on your prize tomatoes look like someone spattered them with brown paint. Within days the stems are streaked black and the fruit is rotting on the vine. That is tomato blight, and it is the single most destructive disease UK gardeners face in late summer.
The good news is that blight is predictable. It needs warm, wet weather and it arrives on the same conditions every year. Learn to spot it early, understand how it spreads, and you can protect your crop - or grow varieties that shrug it off entirely. Here is everything UK gardeners need to know about identifying, treating, and preventing tomato blight.
What Is Tomato Blight?
Tomato blight (Phytophthora infestans) is a fungal-like disease that also attacks potatoes, which is why the two crops often fail together in the same season. It spreads through airborne spores that travel on wet weather fronts, which is why outbreaks tend to arrive after a period of warm, humid, showery weather.
There are actually two separate diseases that gardeners lump together as blight. Early blight (Alternaria) starts as small brown spots with yellow halos on lower leaves and spreads slowly. Late blight is the real killer - it can destroy an entire plant within a week. Late blight is the one that arrives in August and September after warm, wet spells, and it is the one this guide focuses on.
How to Identify Tomato Blight
Catching blight in the first 48 hours can save the rest of your crop, so learn these four warning signs:
- Brown patches on leaves - irregular, greasy-looking brown or olive-green blotches that start at the leaf edges and spread inward.
- White fungal spores - in humid conditions, a fine white or greyish mould appears on the underside of the infected patches, usually early in the morning.
- Black streaks on stems - dark brown or black lesions that spread up the main stem and onto leaf stalks.
- Rotting fruit - firm, greasy brown patches that spread over the fruit surface and quickly turn the tomato to mush.
Check the underside of leaves with a magnifying glass or your phone camera zoomed in. That white spore growth is the giveaway - it is how the disease spreads to neighbouring plants, so the moment you see it, remove the leaf.
How Blight Spreads in UK Gardens
Blight spores need two things to germinate: warmth above 10Β°C and liquid water on the leaf surface. A warm August day followed by rain or heavy dew creates the perfect infection window. Spores blow in from infected potato fields, allotments, or neighbouring gardens, land on wet leaves, and germinate within hours.
This is why blight outbreaks cluster. One infected plant in a damp, crowded greenhouse can seed the whole crop within a week. It also explains why greenhouses and polytunnels actually help - they keep rain off the leaves - and why outdoor cordon tomatoes in a wet summer are the most vulnerable of all.
Prevention: Stop Blight Before It Starts
Blight has no cure, but it has plenty of weaknesses. Every hour you spend on prevention now is worth ten hours of triage later.
Grow Resistant Varieties
This is the single most effective change you can make. UK breeders have developed tomato varieties with strong blight resistance, and they taste just as good as the classics. Suttons Tomato Seeds F1 Crimson Crush carries the Ph-2 and Ph-3 resistance genes and produces large, sweet, classic-tomato fruit.
For cherry lovers, Suttons Tomato Seeds Crimson Cherry F1 offers the same resistance in a bite-sized fruit that crops heavily right through to October. Switching to resistant varieties is not a compromise - it is the difference between harvesting and watching your plants die.
Keep Leaves Dry
Water at the base of the plant, not over the top. A Hozelock Superhoze Expanding Hose aimed at the soil line keeps foliage bone dry, and dry leaves mean spores cannot germinate. Water early in the morning so any accidental splashes dry off before nightfall, and never water in the evening during humid spells.
Ventilate and Space
In a greenhouse or polytunnel, open vents and doors on warm days to keep air moving. Crowded plants trap humidity and create microclimates where blight thrives. Remove the lower leaves of cordon tomatoes up to the first truss - this improves airflow around the base of the plant and removes the leaves most likely to pick up soil splash.
Apply a Preventive Spray
If blight is in your area (check local allotment forums or the RHS blight report), start spraying healthy plants before symptoms appear. Westland Fungus Guard Fungicide Spray is a ready-to-use option that controls fungal diseases on fruit and vegetables, while Liquid Copper Fungicide is the traditional copper-based treatment used by organic growers. Spray every 7-10 days during high-risk weather, and always reapply after heavy rain.
Keep Plants Strong
A healthy, well-fed plant fights off infection far better than a hungry one. Feed regularly through the season with Concentrated Tomato Plant Food to keep growth steady, and avoid stress from drought or waterlogging. Stressed plants lower their natural defences just when blight pressure is highest.
What to Do When Blight Hits
There is no cure for late blight - the RHS is blunt about this, and so are we. Once the disease takes hold in the plant tissue, no spray can save that plant. What you can do is limit the damage:
- Remove infected foliage immediately. Cut off every leaf with brown patches, bag it, and bin it. Never compost blighted material - spores survive in compost heaps.
- Remove and destroy badly infected plants. If the stem is streaked or the fruit is rotting, pull the whole plant, bag it, and put it in the bin. Leaving it in place just spreads spores to everything else.
- Harvest green fruit early. Pick any healthy-looking green tomatoes and ripen them indoors on a windowsill. Fruit that has not yet developed brown patches will ripen fine.
- Spray the survivors. Give remaining healthy plants a preventive dose of Westland Fungus Guard Fungicide Spray or Liquid Copper Fungicide immediately to slow spread.
- Do not plant potatoes nearby next year. Blight survives in infected tubers and soil, so rotate your solanum crops (tomatoes and potatoes) to a fresh bed.
Can You Save Tomatoes from a Blighted Plant?
Usually yes, if you act fast. Green tomatoes with no brown patches can be picked and ripened indoors, away from the disease. Bring them inside, lay them in a single layer on a windowsill or in a cardboard box with a ripe banana (the ethylene speeds ripening), and they will colour up over 1-2 weeks. Check them daily and discard any that develop soft patches.
For outdoor plants hit by an early September blight, covering with Christow Greenhouse Fleece Cover on dry nights can buy you a few extra weeks of ripening, though it is no substitute for resistant varieties.
Frequently Asked Questions
Final Verdict
Tomato blight is the UK's most destructive garden disease, but it is also one of the most avoidable. Grow a resistant variety like Suttons Tomato Seeds F1 Crimson Crush or Suttons Tomato Seeds Crimson Cherry F1, water at the base so leaves stay dry, keep greenhouses ventilated, and spray preventively when the weather turns warm and wet. If blight still finds you, act in the first 48 hours - remove the infected plant, harvest the green fruit, and protect the survivors.
Do that, and you will be eating homegrown tomatoes in September while your neighbours are binning blackened plants. And if you are growing in pots this year, our complete container tomato guide covers the whole process from seed to harvest.
Alex Green writes about vegetable growing, plant care and small-space gardening for MyLushGarden.
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Last reviewed: August 2, 2026 Β· Evidence-based content Β· Contains affiliate links