The Daiō Wasabi Farm in Hotaka, about 30 minutes north of Matsumoto by train, is Japan's largest wasabi farm and one of the prettiest stops on the Azumino plain. Spring-water channels run through the fields in long parallel rows, with the green wasabi plants growing in the gravel between them. The farm shop sells wasabi ice cream, wasabi soba and (more usefully) freshly grated wasabi to take away in tubes.
Get there by train to Hotaka station and walk or take the rental cycles. Combine with the Rokuzan Art Museum near the station for a full day out.