The Great Famine was caused by a failure of the potato crop, which many people relied on for most of their nutrition. A disease called late blight destroyed the leaves and edible roots of the potato plants in successive years from 1845 to 1849.

40% of the Irish potato crop was destroyed by late blight in 1845 and almost 100% destruction occurred in 1846 [4]. An estimated 1.5 million Irish died of famine and disease during the late blight epidemic, and a similar number of people emigrated, mainly to North America [5].

1 million people
In 1849, the famine was officially at an end, but suffering continued throughout Ireland. More than 1 million people died between 1846 and 1851 as a result of the Potato Famine. Many of these died from starvation.

Although estimates vary, it is believed as many as 1 million Irish men, women and children perished during the Famine, and another 1 million emigrated from the island to escape poverty and starvation, with many landing in various cities throughout North America and Great Britain.

The potato late blight pathogen was introduced to Europe in the 1840s and caused the devastating loss of a staple crop, resulting in the Irish potato famine and subsequent diaspora.

In 1843 and 1844, blight largely destroyed the potato crops in the Eastern United States. Once introduced in Ireland and Europe, blight spread rapidly. By mid-August 1845, it had reached much of northern and central Europe; Belgium, The Netherlands, northern France, and southern England had all already been affected.

274. Interestingly too as ‘Brougham Villiers’ argued, the ‘Hungry Forties’ became a short-hand term for the whole of the period between 1815 and 1846, i. e. from the imposition of the Corn Law in 1815 until its abolition.

As a direct consequence of the famine, Ireland’s population fell from almost 8.4 million in 1844 to 6.6 million by 1851. About 1 million people died and perhaps 2 million more eventually emigrated from the country.

The famine did not affect all of Ireland in the same way. Only in the small farms of west of Ireland, and in parts of Munster, was the potato in a monopolistic position. It is estimated that at the eve of the famine 30% of Irish people were largely or wholly dependant on potatoes for their food.

The potential economic and social impact of potato late blight is best illustrated by the well-publicized role it played in the Irish Famine in the middle of the nineteenth century. Because of the famine, millions of Irish died or emigrated (Bourke 1993).

P. infestans, the cause of late blight, is a heterothallic fungal-like pathogen, meaning two mating types are required for sexual reproduction and are referred to as A1 and A2. The pathogen is an obligate parasite that cannot survive without a living host.

The potato blight returned to Europe in 1879 but, by this time, the Land War (one of the largest agrarian movements to take place in 19th-century Europe) had begun in Ireland. The movement, organized by the Land League, continued the political campaign for the Three Fs which was issued in 1850 by the Tenant Right League during the Great Famine.

Haverkort et al. (2009) estimated that the global costs and losses due to late blight may take 16% of all global potato production. At 100 €/t the world potato production represents a value of €38 billion today.