What is Potato Blight and what causes it?

Potato blight is a fungal disease that can devastate a potato crop. It attacks the foliage and tubers and if left can cause your crop to rot. Potato blight starts with black spots appearing on the leaves and eventually turning yellow. It can take hold in a matter of days and as long as you act fast, by cutting back the foliage, the tubers can be left in the ground to mature.

Blight normally occurs in wet, warm and humid conditions, especially after a period of dry weather followed by a period of rain.

Blight can also affect tomatoes.

How to avoid potato blight

Buy in new seed potatoes that are certified disease free. Saving your seed potatoes from previous years or using shop bought potatoes can lead to problems later in the year.

The ‘Sarpo’ cultivars such as Sarpo Mira offers excellent blight resistance and can be bought from most garden centres or online. Most early variety potatoes offer very little resistance to blight but they are generally harvested before it strikes.

Earthing up your potatoes or covering the young plants with organic matter can help stop the spores washing into the soil, which can help protect the tubers. Covering the plants with organic matter can help with water loss, meaning you don’t have to water as often. When you do water your plants, do so at the base of the plant.

What to do if you get blight

At the first sign of blight, remove all the foliage from the plant. Leaving the tubers in the ground for 2-3 weeks will help ensure the spores on the surface of the soil are dead. It’ll also harden the skin of the tubers. Dry the tubers before storing them in a cool, dry, dark place.

What to do with infected foliage

When it comes to the infected foliage, general advice is to either burn or dispose of it, never add it to the compost heap as this may cause problems later. Another method is to bury the foliage deep underground.