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Irish Times

Why do my potatoes look warty – and are they safe to eat?

Why is the skin of my home-grown potatoes covered in patches of what almost looks like a rough, warty growth, and are they still safe to eat? Andrew Cullinane, Co Galway It sounds as if your potatoes have a disease known as common scab. The good news is that while it sounds horrible and looks unsightly, it doesn't affect the flavour or edibility of the tubers themselves. Symptoms of common scab, which is naturally present in many soils as a microorganism known as Streptomyces scabium, are exacerbated by the developing baby potatoes being exposed to periods of sustained dry weather like those experienced in Ireland this spring and summer. It's also more likely to affect potatoes grown in a limy soil, or a soil to which lime has recently been applied. The rough, scabby growth on the skin of your potatoes is actually the plant's way of limiting damage to the flesh of the tubers. There is no treatment for this disease, which can also be inadvertently introduced into a garden or allotment by way of infected seed potatoes. For this reason, it's always recommended to source the latter from reliable suppliers as certified free from disease. It's also a good idea to keep young plants sufficiently watered during any prolonged dry spells. Crop rotation will help too, by preventing a build-up of the disease in the soil. READ MORE It's worth noting that some varieties, typically those with thinner skins, are more vulnerable to common scab than others. Examples of varieties with good resistance to the disease include 'Connect' (maincrop); 'Cammeo' (maincrop) and 'Charlotte' (early). Importantly, all these varieties also have good resistance to blight, a far more destructive disease that can wipe out an entire crop in a bad year. [ Is it too late to save my blighted potato plants? Opens in new window ] If your potatoes are a maincrop variety that you're planning on storing to use over the coming months, then take extra care to give them a cool, dark, dry spot to reduce the possibility of the scabbed areas of the tubers becoming infected by soft rot, which could then spread to the rest of the potatoes and destroy them. For the same reason, make sure to examine the stored tubers regularly to check for any early signs of rot, discarding any that you find (but not in the compost heap). Finally, for obvious reasons, also avoid reusing any of them as seed potatoes next spring. An interesting footnote to the above is that the microorganism that causes common scab in potatoes belongs to the same Streptomyces genus that's also played a vital role in the production of the majority of antibiotics. Just a few years ago, a new soil-dwelling species of Streptomyces was discovered by scientists in west Fermanagh, which promises significant potential as a new generation of antibiotic. How amazing is that?