🐛✗ Tested and false“Spraying potatoes with a copper product like Bordeaux mixture will cure or prevent blight”
There is currently no fungicide of any kind, copper-based or otherwise, sold to home gardeners for use against potato blight in the UK. That includes Bordeaux mixture and similar copper products, which growers once used to coat leaves ahead of an outbreak; even at that, they were a preventative barrier rather than a cure, and did nothing for a plant already showing symptoms.
What to do: Skip the search for a blight spray and put the effort into forecasting risk, choosing resistant varieties and stripping infected foliage the moment it appears, since no product on general sale does the job.
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“Blight is only a problem in wet years; a dry summer is safe”
Infection needs surface wetness lasting several hours, not a whole rainy season, so a single humid, dewy or drizzly spell can start an outbreak even inside a summer that is dry overall. Wetter summers do carry more risk simply because damp spells happen more often, but that is different from saying a dry-looking year is safe.
What to do: Judge risk spell by spell through the growing season rather than by the summer's general character, and check plants closely after any stretch of warm, damp weather even in an otherwise dry year.
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“Blight-resistant varieties like the Sarpo types are immune to blight”
Named resistant cultivars carry real, useful resistance, but none is immune; they can still develop blight if favourable wet conditions persist for long enough. Resistance is also not permanent: some varieties once sold as resistant no longer perform that way because the pathogen itself has changed over time.
What to do: Grow a resistant variety to lower the odds and buy extra time, but keep checking for symptoms rather than assuming a resistant crop can be left unwatched.
In Scotland: A Scottish agricultural advisory source states plainly that no current variety is totally resistant, for either leaf or tuber blight.
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“If tubers from a blighted crop look clean with no blemishes, they're safe to store as usual”
Tuber blight begins as decay just below the skin before it turns into visible soft rot, so a tuber can already carry the infection while still looking sound on the outside at harvest. That is why the standard advice for a blighted crop is to use the tubers promptly and avoid storing them at all where possible, rather than storing them through winter as usual.
What to do: Treat tubers lifted from a blight-affected crop as a use-soon batch rather than a long-term store, even when none of them show visible marks when you dig them up.
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- RHS: Potato and tomato blightTuber blight shows as reddish-brown decay below the skin, progressing to soft rot, and advises using tubers from blighted crops as soon as possible and avoiding storage where possible.
“Rotating where you grow potatoes each year protects the crop from blight”
Rotation is recommended for blight, but for a narrower reason than most gardeners assume: it targets resting spores that can persist in the soil, not the wind-blown spores that account for the great majority of garden infections. Because most new outbreaks arrive on the wind from other gardens, allotments and farms rather than from last year's potato bed, rotation closes off one route while leaving the dominant one wide open.
Our read This is a real difference from a soil-borne disease like clubroot, where staying off infected ground for years is the main defence. For blight, rotation is a minor supporting measure, not the primary one.
What to do: Keep a rotation for general soil health and other diseases, but rely on forecasting, resistant varieties and prompt removal of infected foliage for the bulk of blight protection, since rotation alone won't stop spores blowing in from elsewhere.
In Scotland: Discarded potato dumps left over winter are flagged as a key early blight source for Scottish growers, so clearing those matters at least as much as which bed potatoes go into.
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“A homemade baking soda (sodium bicarbonate) spray controls potato blight”
A university-compiled bibliography of sodium bicarbonate research covers a long list of true fungal diseases, powdery mildews, apple scab, early blight and postharvest rots among them, but contains no study on late blight specifically. That gap is telling: potato blight is caused by an oomycete, not a true fungus, so the mechanisms documented for bicarbonate against fungal pathogens were never tested against the organism that actually causes this disease.
Our read Absence of a study is not the same as a disproven claim, but it means there is no research base to point to for this specific use, only research on a biologically different group of pathogens.
What to do: Don't rely on a baking soda spray to protect a potato crop from blight. There is no evidence it works against this particular organism, and blight can wreck a crop within days once conditions are right.
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“Earthing up potatoes properly protects the tubers from blight”
Both RHS and Garden Organic confirm earthing up (or mulching thickly) reduces tuber infection by creating a soil barrier against blight spores washed down from infected foliage. It reduces, rather than eliminates, tuber infection risk.
What to do: Keep potatoes well earthed up or mulched, especially once foliage shows blight symptoms, to cut down spore contact with developing tubers underneath.
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- RHS — Potato blightEarthing up potatoes well provides some protection to the tubers from blight spores washed down into the soil from lesions on the leaves or stems.
- Garden Organic — Potato blightEarthing-up potatoes, or mulching the soil with a thick layer of hay, straw or other organic material, can reduce the levels of tuber infection.
