Music Late blight, or potato blight, is a fungal disease that can devastate healthy potatoes with alarming speed. Just look at this sorry specimen! Knowing how to identify blight and what action to take is essential if you want to save some of your crop. Here are our top tips. Symptoms of late blight include brown black spots on the leaves which can spread to the stems as brown patches. The undersides of leaves can take on a white downy appearance in wet weather. Blight can spread quickly, causing complete collapse of the foliage.
Severe cases will leave the potatoes themselves with sunken patches and rotten brown flesh. As soon as you spot blight, cut out light infections with sharp pruners. To avoid spreading disease between plants wipe the blades with disinfectant after each cut, and don’t touch the healthy foliage. If more than a tenth of the foliage is infected, you’ve reached the point of no return. Cut the stems back to the ground and harvest the tubers for immediate use, or leave them undug for 3 weeks, then lift for storage. Some varieties show resistance to blight, so plant these types next year.
For complete peace of mind always buy fresh certified diseasefree seed potatoes. Blight is more likely to strike in warm, moist conditions. If you need to water your plants, try not to wet the leaves. Water in the morning so that any excess moisture soon evaporates. Proper earthing up, or hilling, of your potatoes can improve moisture levels while mulching will lock in moisture and it will take longer for blight spores to reach the tubers below. Blight can overwinter on infected tubers, so make sure you dig out every last potato at harvest time.