Irish famine was caused by

The Irish famine was caused by Phytophthora.
Irish famine is also known as the Great Irish famine, which occurred in Ireland in 1845 - 49 when the potato crop failed in successive years. The crop failures were caused by late blight, a disease that destroys both the leaves and the edible roots, or tubers, of the potato plant. The causative agent of late blight is the water mold Phytophthora infestans.