Potato blight (Phytophthora infestans) is a fungal infection which thrives in damp, mild weather conditions. This fungus firstly damages the leaves and stalks above ground before penetrating beneath the surface soil to destroy the potato tubers. 

It was a new disease which was first noticed on the eastern seaboard of the United States in 1843, spreading rapidly from a New York – Philadelphia axis northwards and westwards to reach both the Maritime Provinces and the Great Lakes area by 1845. 

By June 1845 it had spread to Flanders, the rest of Belgium, the southern Netherlands and adjacent parts of the German Rhineland. By late August, the disease had expanded rapidly over much of northern and western Europe including all of England and Wales and eastern Ireland. 

Its initial expansion was linked to the development of an international trade in seed potatoes but, once established, the blight spread extremely rapidly in the particularly damp summer of 1845. By the start of September the blight had reached all parts of Ireland and Scotland. 

However, some areas escaped the full impact of the disease in the first year –it was the more prosperous eastern regions of Ireland which were initially most deeply affected. Almost the whole crop, however, failed in 1846.

This piece is based on the Atlas of the Great Irish Famine edited by John Crowley, William J. Smyth and Mike Murphy and its contents do not represent or reflect the views of RTÉ.