Tomato blight is a fast-moving disease that turns healthy plants into brown, collapsing mush within days, usually striking outdoor tomatoes in the warm, wet weather of July and August. The hard truth first, because it is the thing everyone searching for a cure needs to hear: once late blight has taken hold there is no spray that will save that plant. What you can do is act fast to rescue the fruit, stop it spreading, and make sure it never wrecks your crop again. This guide covers how to tell blight from the harmless problems it gets confused with, what to do the moment you see it, and the one change that actually works for next year.
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I lost an entire outdoor row to blight one August in Oxfordshire, the kind of wet muggy August we get every few years, and it happened so fast I genuinely thought someone had poured weedkiller over the bed. One evening the plants were fine, three days later they were black and stinking. That row taught me more than any success ever did, and almost everything I now do with tomatoes, from where I plant them to which varieties I choose, traces back to that week. So this is not a cheerful guide, but it is an honest one, and the honest version is the one that saves your crop.
What Tomato Blight Actually Is
Tomato blight is late blight, caused by a fungus-like organism called Phytophthora infestans, the same organism responsible for potato blight and, historically, the Irish potato famine. It is not strictly a fungus, which matters because it means many ordinary fungicides do nothing against it. The spores blow in on the wind and thrive in exactly the conditions a British summer serves up on repeat: warm days, cool nights, high humidity and wet foliage. Outdoor tomatoes are hit hardest because rain lands on the leaves and the wind carries the spores straight in. Greenhouse plants are much safer, simply because the spores struggle to reach them, though an open door or vent on a muggy day can still let blight in.
How to Tell If It Is Actually Blight
Half the plants people declare dead from blight have something far less serious, so before you pull anything up, look properly. Blight has a distinct signature. It starts as irregular brown or grey-green watery patches on the leaves, often with a paler yellowish halo around the edge, and it spreads fast, in days not weeks. In humid weather you may see a faint white fuzzy growth on the undersides of affected leaves, which is the organism itself sporing up. From the leaves it moves to the stems, leaving dark brown or black streaks, and finally to the fruit, which develops firm brown leathery patches, usually starting on the shoulders where spores land from above. The overall impression, and this is the tell every experienced grower recognises, is of a plant that looks scorched, as though it has been hit by frost or a blowtorch.
What it is often confused with matters just as much. Blossom end rot is a sunken brown patch on the bottom of the fruit only, with no leaf damage, and it is a watering and calcium problem, not a disease. Simple leaf yellowing from the bottom up is usually feeding or watering, covered in my guide to caring for tomato plants. Early blight, despite the shared name, is a different and much slower disease showing as brown spots with concentric rings like a target, and it rarely destroys a plant the way late blight does. If the damage is slow and patchy, you probably do not have late blight. If it is fast and spreading and the plant looks scorched, you do.
Early Blight and Late Blight Are Not the Same Thing
This trips people up constantly, so it is worth being clear. Late blight is the fast, plant-killing disease this article is mostly about, the Phytophthora one. Early blight is caused by a completely different organism, Alternaria, and shows as dark spots with a bullseye pattern of concentric rings, usually on the older lower leaves first. Early blight is a nuisance that reduces vigour and can be managed by removing affected leaves, improving airflow and keeping the plant well fed. Late blight is the emergency. If your searches keep turning up American advice about spraying for blight, bear in mind much of it addresses early blight, which behaves differently, and that the fungicides they name are often not available to UK home gardeners anyway.
What to Do the Moment You See Late Blight
Speed is everything, because you are no longer trying to cure the plant, you are trying to save the crop and protect everything nearby. First, if you have caught it very early on just one or two leaves, remove them immediately, bag them and bin them, do not compost them. Sometimes, in a dry spell that follows, that buys you time. More often the weather stays muggy and it spreads regardless.
Once it is into the stems, accept the plant is finished and act decisively. Cut off and harvest every fruit that is still firm and unblemished, even the green ones, because green tomatoes ripen perfectly well indoors on a windowsill or in a drawer with a banana, and they make excellent chutney besides. Then pull up the whole plant, roots and all, bag it and put it in the household waste or take it to the tip. Do not compost blighted material and do not leave it lying on the plot, because it sheds spores onto everything around it. Wash your hands and tools before touching healthy plants. The goal at this stage is containment: one blighted plant dealt with fast is a disappointment, a whole bed left to rot is a disaster that seeds next year’s trouble too.
The Truth About Sprays and Cures
This is the section people least want to read and most need to. There is no home garden spray in the UK that cures late blight once a plant is infected. The old copper-based preventative sprays that gardeners used for decades are no longer available to amateurs here, and even those were preventatives, applied before infection to slow it, never cures. So when you search for a tomato blight cure or the best fungicide for blight and find products promising miracles, treat them with deep suspicion, because the science is simply not on their side for late blight. Home remedies like milk sprays, bicarbonate and the rest may help very slightly against some other tomato problems, but they will not stop late blight. Anyone selling you a cure is selling you hope, not results. The honest defence is not a bottle, it is everything in the next two sections.
How to Stop Blight Getting a Foothold
Since you cannot cure it, prevention is the whole game, and a few habits genuinely cut your risk. Grow under cover if you can: a greenhouse, polytunnel or even a simple rain cover over outdoor plants keeps the leaves dry and the spores off, and dry leaves are the single biggest factor. Water the soil at the base, never the foliage, and water in the morning so any splashes dry quickly, the same discipline that helps with most tomato troubles, covered in how often to water. Space plants generously and remove lower leaves so air moves freely and the canopy dries fast after rain. Keep tomatoes and potatoes well apart, since blight jumps between them, and never plant tomatoes where blighted potatoes grew the year before. And keep plants strong with steady feeding, because a vigorous plant shrugs off a light early hit far better than a stressed one, which is where good tomato growing from the start pays off.
The One Thing That Actually Works: Resistant Varieties
After that August wipeout, the change that made the real difference was not a spray or a clever trick, it was switching varieties. Modern blight-resistant tomatoes have been bred specifically to withstand late blight, and while no variety is completely immune, a good resistant one will often sail through a wet summer that flattens the old favourites beside it. The standout for UK gardeners is Crimson Crush, an F1 variety bred for genuine blight resistance that still produces large, properly flavoured tomatoes rather than the tough tasteless fruit that early resistant varieties gave you. Others worth knowing are Mountain Magic and the cherry variety Lizzano. If you garden outdoors in a wet part of the country, or you have been burned by blight before, a resistant variety is the best decision you can make. Thompson and Morgan stock Crimson Crush and other resistant varieties as both seeds and young plants, and it is the one seed choice I would not compromise on after what I have seen blight do.
One honest caveat: the blight organism is always evolving, and a variety that resists today’s strains may meet a new one in future, so resistance is a strong advantage rather than a cast-iron guarantee. Combine a resistant variety with the good habits above, and you have done everything a gardener realistically can.
Blight in the Soil and Next Year
A common worry is that blight lurks in the soil ready to strike again, but late blight does not generally survive winter in UK garden soil on its own. It overwinters mainly in living plant material, most often infected potato tubers left in the ground, which is why clearing every last potato at harvest matters. So you do not need to sterilise your soil or abandon the bed. What you should do is practise good potato hygiene, rotate where you grow tomatoes and potatoes, clear all debris at the end of the season, and start next year with resistant varieties and dry-leaf discipline. Blight is a weather disease as much as anything, so some summers will always be worse than others, but a gardener who does these things will keep cropping tomatoes through years that leave their neighbours with black stalks.
Frequently Asked Questions
Can you save a tomato plant with blight?
No, not once late blight has taken hold. There is no cure that will bring an infected plant back. What you can do is harvest all the firm, unblemished fruit to ripen indoors, then remove and bin the whole plant quickly to stop it spreading to others. Caught on just one or two leaves in dry weather, prompt removal of those leaves occasionally halts it, but usually the plant is lost.
Can you eat tomatoes from a plant with blight?
Yes, if the fruit itself is firm and unmarked. Pick every sound tomato, including green ones, and ripen them indoors on a windowsill or in a drawer. Do not use fruit showing the brown leathery patches of blight. Green tomatoes also make excellent chutney, which is the traditional way of rescuing a blighted crop.
What is the difference between early blight and late blight?
They are different diseases. Late blight (Phytophthora infestans) is the fast, plant-killing one that turns tomatoes brown and scorched in days. Early blight (Alternaria) is slower, showing dark spots with concentric target-like rings usually on lower leaves, and it weakens rather than destroys the plant. Late blight is the emergency; early blight can be managed.
Does tomato blight stay in the soil?
Not usually. Late blight does not generally survive UK winters in garden soil by itself. It overwinters mainly in living material, most often infected potato tubers left in the ground. Clear all potato and tomato debris at the end of the season, rotate your crops, and you can safely grow tomatoes in the same bed again.
What is the best blight-resistant tomato?
For UK gardeners, Crimson Crush is the standout: a blight-resistant F1 variety that still gives large, well-flavoured fruit. Mountain Magic and the cherry variety Lizzano are also good. No variety is completely immune, since the blight organism keeps evolving, but a resistant variety combined with dry-leaf growing habits is the most reliable defence there is.
Can I spray to prevent tomato blight?
There is no effective blight cure available to UK home gardeners, and the old copper-based preventative sprays are no longer sold to amateurs here. Home remedies will not stop late blight either. Your defences are resistant varieties, keeping foliage dry, good spacing and airflow, and keeping tomatoes away from potatoes.
A Sensible Place to Start
If blight has just hit you, do not waste money on a cure that does not exist. Harvest every firm tomato to ripen indoors, pull and bin the infected plants fast, and keep your tools and hands clean around what is left. Then make next year different: grow a resistant variety like Crimson Crush, keep the leaves dry by watering at the base and giving plants room to breathe, and keep your tomatoes clear of the potato patch. Blight is a genuinely hard disease and some wet summers will test you whatever you do, but these few decisions are the difference between the odd lost plant and a black, empty bed. After that August of mine, I have rarely lost more than a plant or two, and never a whole crop again.