Late or Irish Blight of Potatoes and Tomatoes

Phytophthora infestans


A fungal disease that usually starts on the leaf margins as coloured patches. The patches enlarge and go dark brown with age. A white fungal growth may develop on the underside of leaves and around the spots in humid conditions. Stems may become infected. Tubers are infected as spores wash down to the soil from the plant. Brown to purplish black sunken areas appear on the tuber when the tuber is cut, reddish brown areas can be seen in the flesh beneath the lesions. Tubers that come in contact with diseased tops may develop the disease in storage.

Species Affected:

Potato, Tomato and other Solanaceae species.

Sebago and Sequoia Potato varieties appear to be more tolerant than other varieties.


Favoured by humid weather with warm days and cool nights.

Spore spread by wind and raindrop splash.

Life Cycle:

Origin and History:



Management and Control:

Plant healthy tubers.

If the crop is infected then remove tops before harvest.

Remove all tubers from the ground.

Separate diseased tubers form healthy ones before storage.

Apply fungicides.

Related and Similar Species:




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