Bo Melander from Aarhus University in Denmark presented results from the HighCrop project focussing on specific management strategies of perennial weeds, particularly common couch grass (Elytrigia repens) and perennial sow thistle (Sonchus arvensis).
A combination of strategies are considered including; ensuring flat fields, using competitive crops in the rotation and maintaining soil fertility to feed the crop and starve the weeds. To control severe infestations of couch, Bo advocates employing intensive summer cultivations. This involves harvesting the previous crop in June, repeated cultivations and then sowing a catch crop such as mustard which is then ploughed in during Autumn. He also highlighted the importance of removing couch rhizomes from the field, which can then be composted, and emphasised ploughing, rather than min-till, as essential for perennial weed control in organic systems.
By comparing the relative effect of factors such as crop species or cultivations on weed levels over several rotations and sites Bo identified; summer cultivations, adding slurry and winter rye or potatoes as most effective in controlling Couch. Sow thistle is also best controlled by mowing during the ley phase.