What was the original cause of the great famine in Ireland? A tv doc linked it to a volcano...?

Phytophthora infestans is the name of the blight that killed the potatoes. It's possible, I suppose, that a volcanic eruption helped create ideal conditions that this mold thrived in, but it's the water mold that killed the potatoes, not an ash cloud (directly). (Not to mention political realities that exacerbated the problem)