Potato blight is a fast-moving disease that turns potato foliage brown and collapsing within days, usually in the warm, humid weather of July and August, and it can rot the tubers underground afterwards. The single most useful thing to know is this: the moment you see it, cut all the foliage off at ground level and bin it, then leave the tubers in the ground for at least two to three weeks before lifting. That one action saves most of the crop. There is no spray available to UK home gardeners that will cure it, so everything else is about lifting early, choosing resistant varieties, and not carrying the problem into next year.
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The August my tomatoes went black, the potatoes two beds along went the same way about four days later, which is how I learned the hard way that they are the same disease. I made every mistake available. I dithered for a week hoping it would pass, then dug the lot up in a panic while the soil was still covered in spores, and half of what I stored turned to brown slime in the sack by October. Nothing teaches you the right sequence quite like opening a sack of rotten potatoes in a cold shed. This guide is that sequence, in the order it actually needs doing.
What Potato Blight Is and Why It Spreads So Fast
Potato blight, or late blight, is caused by Phytophthora infestans, a fungus-like organism rather than a true fungus, which is why many ordinary garden fungicides do nothing against it. It is the same organism that causes tomato blight, and it moves freely between the two crops, which is why keeping them apart matters. It is also the disease behind the Irish potato famine, which tells you something about how destructive it can be when conditions suit it. Spores blow in on the wind, land on wet foliage, and germinate in warm humid weather. Two consecutive days of minimum temperatures above 10C with long spells of high humidity is the classic trigger, conditions a British summer produces reliably from July onwards. Once infection starts in a damp crop, it can go from a few spots to a collapsed bed in under a week.
How to Recognise Potato Blight
It starts on the leaves as dark brown or blackish patches, often at the leaf tips and edges first, frequently with a pale yellowish-green halo around them. In humid weather, look at the undersides of affected leaves in the morning and you may see a faint white fuzzy growth, which is the organism sporulating. From there it moves fast: whole leaves brown and shrivel, dark streaks appear on the stems, and the plant takes on a scorched look, as though someone has gone over it with a blowtorch. There is often a distinctive musty, rotten smell to a badly affected bed on a still day.
Below ground, infected tubers develop sunken dark patches on the skin, and cutting one open shows a reddish-brown rusty marbling spreading in from the surface. Blighted tubers frequently go on to develop soft, foul-smelling secondary rots in storage, which is where most of the damage is actually done. Do not confuse blight with the ordinary yellowing and dying back of haulms at the end of the season, which is simply the crop finishing, or with the slower spotting of early blight, a different and far less serious disease. Blight is fast and it stinks. If in doubt, look for how quickly it is spreading, because that is the tell.
What to Do the Moment You See It
Act the same day. Cut every bit of foliage and stem off at ground level, and do not leave the cuttings lying on the bed. Bag them and put them in the household waste or take them to the tip. Do not compost blighted haulms, because a garden heap does not get hot enough to reliably kill the spores, which is worth remembering even if you are otherwise keen on composting at home. Removing the foliage stops the disease travelling down the stems into the tubers, and that is the whole point of doing it quickly.
Then leave the tubers in the ground. This is the part people get wrong, myself included that first year. Spores from the dead foliage are sitting on the soil surface, and if you dig immediately you drag your potatoes up through them and infect the crop on its way out. Wait two to three weeks. The spores on the surface die off, the skins on the tubers set firmer, and what you lift then is far more likely to store. When you do dig, do it on a dry day, leave the potatoes on the surface for a few hours to dry, and inspect every single one. Store only clean, firm, unmarked tubers, because one infected potato will rot an entire sack. Anything with a sunken dark patch gets eaten straight away if sound inside, or binned.
The Truth About Spraying
For years UK gardeners protected potatoes with copper-based or mancozeb sprays applied before infection. Those products are no longer available to amateur gardeners here, and in any case they were preventatives that had to be on the leaves before spores arrived, never cures for an infected plant. Commercial growers still spray, on a schedule, with products and equipment not sold to home gardeners. So if you are searching for a potato blight treatment or the best fungicide for blight, the honest answer for a UK home garden is that there is not one worth buying. Home remedies do not work against this organism either. That is not a counsel of despair, because the cultural methods below genuinely do work, but it does mean the money is better spent on the right seed potatoes than on a bottle of anything.
The Early Potato Escape Route
The most reliable defence in a British garden is timing, not chemistry. Blight arrives from mid-July onwards in most years. First earlies planted in March are ready to lift from late June, which means the crop is out of the ground and in the kitchen before the disease turns up at all. In twenty years I have almost never lost a first early to blight, and I have lost plenty of maincrops. Second earlies mostly get away with it too. Maincrops are the vulnerable ones, sitting in the ground through August and September precisely when conditions favour the disease. So if blight is a recurring problem on your plot, the simplest fix is to grow more earlies and fewer maincrops, which is worth thinking about when you order your seed potatoes in winter. My guide to when to plant potatoes covers the timings for each type.
Blight Resistant Varieties
If you want maincrop potatoes and you garden somewhere wet, resistant varieties are the real answer. The standouts by a distance are the Sarpo family, bred in Hungary and trialled in Wales: Sarpo Mira and Sarpo Axona have the strongest late blight resistance available to gardeners, scoring top marks in commercial evaluations, with the bonus of drought tolerance and vigorous foliage that smothers weeds. They are floury maincrops, excellent for mash, chips and baking, and they store for a long time. Cara, Valor and Setanta also carry useful resistance without being quite in the same class. Availability moves around between suppliers and seasons, so check who has them when seed potato stock lands from around December, and order early because the resistant varieties sell out first in a year following a bad blight summer.
One honest caveat, the same one that applies to tomatoes: the blight organism keeps evolving, and new strains have already eroded the resistance of some older varieties. Resistance is a very strong advantage rather than a permanent guarantee. Pair it with the habits below and you have covered everything a gardener realistically can.
Reducing the Risk Next Year
A few practical habits make a real difference. Earth up generously, because a deep covering of soil stops spores washing down from the foliage onto the tubers, and shallow-covered potatoes are the ones that rot. Space plants properly so air moves through and foliage dries quickly after rain, and water the soil rather than the leaves. Keep potatoes and tomatoes well apart, and never plant either where blighted potatoes grew the previous year. Clear every last tuber at harvest, because the disease overwinters mainly in living potatoes left in the ground, and next spring those volunteers come up carrying it. Rotate where you grow them, and never plant supermarket potatoes or your own saved tubers from a blighted crop, since certified seed is the one place not to economise. Get all this right and you will still lose the odd year to a filthy August, but you will keep cropping when others do not. More on the basics in how to grow potatoes and common potato problems.
Frequently Asked Questions
Can you eat potatoes from a plant with blight?
Yes, as long as the tubers themselves are firm, clean and unmarked when you lift and inspect them. Cut out and discard any with sunken dark patches or brown marbling inside. Eat questionable ones straight away rather than storing them, because one infected tuber will rot a whole sack.
Should I dig up potatoes if they have blight?
Not immediately. Cut off and bin all the foliage first, then leave the tubers in the ground for two to three weeks. This lets the spores on the soil surface die off and the tuber skins set, so the crop is far less likely to be infected on the way out and much more likely to store.
Does potato blight stay in the soil over winter?
Not usually on its own. It survives mainly in living potato tubers left in the ground, which then sprout as volunteers the following spring and carry the disease. Clear every tuber at harvest, pull up any volunteers, and rotate your crops, and the soil itself is not the problem.
What is the best blight resistant potato?
Sarpo Mira and Sarpo Axona have the strongest late blight resistance available to UK gardeners by a clear margin, both maincrops with a floury texture suited to mash, chips and baking. Cara, Valor and Setanta offer useful but lesser resistance. No variety is permanently immune, because the blight organism continues to evolve.
Can you spray potatoes for blight in the UK?
Not effectively as a home gardener. The copper and mancozeb-based preventatives once used by amateurs have been withdrawn from the UK amateur market, and they were preventatives rather than cures in any case. Commercial growers use products and equipment not sold to home gardeners. Timing, resistant varieties and good earthing up are your realistic defences.
Why do first early potatoes avoid blight?
Because they are harvested before the disease usually arrives. Blight typically strikes from mid-July onwards, while first earlies planted in March are ready to lift from late June. Maincrops sit in the ground right through the risk period, which is why they suffer most. Growing more earlies is the simplest way to dodge blight altogether.
A Sensible Place to Start
If blight has just hit your potatoes, do three things today: cut the foliage off at ground level, bag it and bin it, and then leave the tubers alone for a fortnight. That sequence saves more crops than anything else in this guide, and it is exactly what I failed to do the year I lost half a sack to rot in storage. Then plan next year around timing rather than treatment: more first earlies lifted in June, a resistant maincrop like Sarpo Mira if you want potatoes for storing, generous earthing up, and not a single tuber left in the ground at harvest. Blight is a weather disease and some summers will beat you whatever you do, but those few decisions turn it from a disaster into an inconvenience.