I took a look in Janken Myrdal's The Agrarian History of Sweden, and I came up empty for any new crops introduced during the era. The Scandinavians had practiced agriculture since the stone age, and they were specializing in growing the hardy rye and barely, since those crops suited the climate. Scandinavia was deeply connected with the rest of Europe long before they noticed how very easy and profitable it was to plunder the continentals. Many graves from earlier periods clearly shows that the elites hoarded Roman luxury items.

One fact he does mention though is that the first appearance of the black rat for Scandinavia is in Viking Hedeby. So there you have it, the Scandinavians' vast maritime enterprises would introduce the most hated vermin among people into Scandinavia.