The reasons for Norwegian emigration in the 1800s were quite complex, but poverty and the struggle to put food on the table were certainly one of them.
The most severe case of blight in Norway was contemporary with the Irish potato famine due to the similar climate, reaching its height in 1846, but lasting from 1845-1849. Its impact was somewhat less severe in Norway only because we were less reliant on potatoes than the Irish were at that point, basing more of our diet on grains and fish. Blight continued to be an issue even after this, but the overall production kept rising due to expansion. By the end of the 1870s, new and more blight-resistant potato varieties were introduced and swiftly adopted.
More potato history (I know you want it.)
Edit: Thank you, griffindd. :)