It is vitally important to understand that throughout the "potato famine" Ireland was a major exporter of food to the rest of the UK.

Irish farmers were growing all kinds of crops. Grains, carrots, cabbage, lettuce, etc, etc. All of these were sold to pay for the oppressive rents that they were forced to pay to English landlords who had stolen all of their land.

The potatoes the Irish grew were for subsistence, because all of the rest of their crops went to market. Even when the potato crops failed, there was more than enough food for everyone in Ireland, if the English would simply suspend rent collection for a short while, until the crop failures had passed.

Many motions to do so were put before parliament. All of them were rejected.

The Irish famine was not caused by a disease. It was caused by the intentional cruelty of the English.