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Potato Blight

How to Identify Potato Blight
The first signs of potato blight are dark brown markings on the edges of the potato plant leaves.

The next stage is that the leaves curl and the whole potato plant wilts and eventually falls over. This happens extremely quickly and the whole process can take only a matter of days.

The picture on the left (click it to enlarge it) shows the first signs of potato blight. If you see this on a couple of your potato plants the only course of action is to cut the plant down to ground level immediately.

This will prevent the disease reaching the potato tubers under the ground.

Burn the foliage immediately because this is a highly infectious disease. The spores will live in the soil for a couple of years if they are not destroyed. The same fungus also causes Tomato Blight.

If the foliage is destroyed immediately Potato Blight is noticed, there is a very good chance that the potato tubers under ground will be unaffected. Growth of the potato tubers underground will be slow when the foliage has been destroyed but they will be edible and will store for some time in the ground. See the picture below to identify if the potato tubers have been affected.

Treatment of Potato Blight
Once you have it there is no treatment. To help avoid potato blight there are two main courses of action:

1. Destroy all infected plants by burning them. Do not plant potatoes (or tomatoes) on the same patch of land without leaving an interval of three years.

2. Spray potato and tomato plants with Bordeaux Mixture (available at most garden centres) in May and June to help prevent infection.

As far as we are aware, eating potatoes infected with potato blight will not cause serious medical problems.

However the picture on the right shows the effects on the tuber if the disease is left to take its natural course. Its not as pretty sight I am sure you will agree,

Crop Rotation
The fungus which causes potato blight goes under the name of Phytophthora infestans. It is spread by either wind or rain in temperatures above 10^oC (50^oF)

Avoid it occurring in subsequent years by good crop rotation and burning all infected plants as soon as the disease is noticed.

The Potato Council have distributed two fact sheets on Potato Blight which can be found here.

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