If you grow potatoes, they’ll almost certainly get blight at some point. The first sign is brown spots on the leaves, which may have yellow borders. This quickly spreads and withers all the leaves, until the plant looks quite dead.
If this happens to you, don’t panic, all is not lost! At least, it probably isn’t. Blight is a fungal infection that attacks the leaves first, but only causes real damage if it gets into the tubers. If you catch it early enough, you may be able to stop it spreading to the tubers at all. Cut the haulms (leaves and stalk) off and take them away. Best practice is to avoid composting them, so the blight doesn’t have the chance to hang around your garden and infect next year’s crop. At this point, do not be tempted to dig up your crop and inspect the damage. Leave them in the ground for a couple of weeks (but not much longer because the slugs will move in). If the weather’s dry, the blight spores will die out on the surface of the soil, for want of anything to eat.
On the other hand, if it’s chucking down with rain, as it was this year when I noticed blight in my potato patch, the spores will wash into the soil and infect the tubers. Oh no, all my precious potatoes are blighted! Well… this is a problem, but it may not yet be catastrophic. Blight takes a while to eat its way through a potato, so while you may see clear signs of damage, there may only be small brown spots that might not even be evident until you peel the potato.
If you cut away the damaged part, blight-infected potatoes are perfectly good to eat. What they’re not good for is storage, as the blight will continue to eat its way through the tubers and when you go to fetch a meal’s worth of potatoes from the sack in your root cellar (you do have a root cellar, don’t you? Garage? Spare bedroom? Understairs cupboard?) you may find nothing but stinking brown mush.
If you have freezer space, you can halt the march of the blight. Don’t freeze potatoes raw, though – that’s a much quicker route to slimy mush. They need at least par-boiling before freezing. While you’re at it, though, you could go one step further and make, for example, frozen oven chips. Peel and cut into chip shapes, then fry until just starting to colour. Personally, I favour beef tallow for frying chips, but other fats and oils will do just as well. Spread them out on a tray to cool, then freeze on the tray before transferring to bags or boxes, or whatever you use in your freezer.
Similarly, potatoes can be prepared for roasting – par-boil then fry briefly (I use sunflower oil for this. Don’t ask me why I have different preferences for different shapes of potato) before freezing. Mashed potato also freezes well, but be sure to divide it into meal-sized portions before freezing.
Generally, I prefer traditional, not electricity-dependent forms of food storage, but when blight strikes, modern technology can help us out.