Weed community and species response to direct-seeded cabbage in the Tokachi district of Hokkaido, Japan

We investigated weed community diversity and density in direct-seeded and transplanted cabbage fields, in order to establish weed management systems for direct-seeded cabbage in the Tokachi District of Hokkaido. In direct-seeded cabbage fields, Rorippa islandica (Oeder) Borb., Chenopodium album L., Persicaria longiseta (De Bruyn) Kitag and Parsicaria nepalensis (Meisn.) H. Gross were especially prominent. Although the composition of weed species did not differ between direct-seeded and transplanted cabbage fields, weed densities increased in direct seeding and R. islandica increased. The cropping season and method of fertilizer application influenced the emergence of R. islandica. During the cabbage growing season, R. islandica began flowering and produced many mature seeds. Some of these seeds emerged from late summer to fall, and winter survival of fall-emerging seedlings influenced the following rotational crops. Although soil-applied herbicide (trifluralin) successfully in the controlled common weeds, it did not control R. islandica. Results indicated that R. islandica should be considered in weed management systems for direct-seeding cabbage production in the Tokachi District of Hokkaido.