Another example: late blight, the mold that attacks tomatoes, potatoes, and a few other plants originated in the Americas and "was a major culprit in the 1840s

Another example: late blight, the mold that attacks tomatoes, potatoes, and a few other plants originated in the Americas and "was a major culprit in the 1840s European, the 1845 Irish, and the 1846 Highland potato famines", according to Wikipedia. Side note: tomatoes and potatoes also originated in the Americas so it's only natural that their associated diseases came from the same region.