Potato blight

Potato blight, also known as late blight to distinguish it from a different potato disease called early blight, attacks the foliage and tubers of potatoes, causing rotting. It is most common in warm, wet weather. The same pathogen also affects tomatoes.

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Leaf lesions caused by potato blight. Image: John Scrace

Quick facts

Common name: Potato blight, late blight
Scientific name: Phytophthora infestans
Plants affected: Potatoes
Main symptoms: Brown & rotting, shrivelled leaves. Decay of tubers
Caused by: Fungus-like organism
Timing: Early summer onwards

What is potato blight?

Potato blight (also known as late blight) is a disease caused by a fungus-like organism (Phytophthora infestans) that spreads rapidly through the foliage and tubers of potatoes in warm wet weather, causing collapse and decay.
It is the most serious and damaging disease of potatoes and can also affect tomatoes (on which it is known as tomato blight) and some ornamental relatives of these two crops. Cases have been recorded on ornamental Solanum species (e.g. S. laciniatum), and very occasionally also on Petunia.

What is early blight of potatoes?

Early blight is a different disease that is found widely in North America, and is commonly reported on the internet. This fungal disease of potatoes is caused by Alternaria solani and A. alternata. It is not a common problem in British gardens, but can be confused with the symptoms caused by the much more common magnesium deficiency.

Symptoms

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