When the chips are down

Fresh potatoes. Photo: PA Photo/thinkstockphotos

Fresh potatoes. Photo: PA Photo/thinkstockphotos

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If you’re already ‘chitting’ your seed potatoes and waiting for those valuable shoots to appear on the tubers before planting out, be aware that this process may be the least of your worries.

While potatoes are generally pretty easy veg to grow given the right soil and situation, some gardeners end up with rotten, foetid tubers which will need disposing of as soon as they are out of the ground.

The most common problem is potato blight, a disease which causes brown or black patches to appear on young leaves from June onwards. The disease spreads rapidly to stems and finally the plant collapses. Spores are washed down to the tubers, resulting in a reddish brown rot and leaving the potatoes a soggy mass.

If you spot it early enough, you can remove infected leaves straight away to stop it spreading and ‘earth up’ or mulch rows with a thick layer of straw or hay. Don’t harvest the crop for at least three weeks after removing the diseased foliage to allow time for the potato skins to thicken up and spores on the surface to die.

Don’t leave blighted tubers in the ground. They will all need digging up as otherwise the spores will spread again, affecting subsequent crops.

Blight usually hits crops in warm, humid conditions from mid-summer onwards. It can be prevented by spraying with a copper-based fungicide, Bordeaux mixture, before symptoms first appear and repeating the treatment every two weeks. But if blight has already appeared, no amount of fungicide will save your crop.

To reduce the risk of blight, practise crop rotation - don’t grow potatoes on the same piece of land more than once every four years - and use deep earthing up to protect the tubers. Grow early potatoes, which are lifted before blight appears, or those which show some blight resistance, including ‘Sarpo Mira’, ‘Colleen’ and ‘Cosmos’. Make sure you always buy certified seed potatoes and don’t save your own tubers.

Other potato problems include blackleg, a bacterial disease that causes the leaves to wilt and the stems to blacken. This usually occurs early in the season and in dry weather. You’ll need to destroy affected plants.

Slugs can be a major pain in heavy and wet soil, and there’s not a lot you can do about them unless you resort to slug pellets or other common slug deterrents. Early potato varieties may be less affected and if you lift your maincrops early you may be able to enjoy them before the slugs do.

The first sign of eelworms, tiny worm-like creatures which burrow into the roots of potatoes, is when plants growing close to each other start dying from the base upwards and the leaves yellow. Tiny reddish brown cysts grow out from the roots, which are the females and full of eggs. Affected plants will soon die.

Scab is another common disease which is common in light soils, caused by a fungus, but although the skins may be damaged, the affected potatoes can be eaten after peeling. To help prevent it, add plenty of organic matter to the soil before planting and water regularly during a long, hot summer.

Find out if there’s a Potato Day near you - many events are publicised online - organised by your local garden club or society, offering growers an ever-expanding choice, advice on dealing with pests and diseases and the chance to talk potatoes with fellow enthusiasts. Events nationwide run through to March.