Perennial weeds in conventional and organic cropping of spring cereals in Finland

A survey of weeds in spring cereal fields was conducted in 16 regions of southern and central Finland in 1997-1999 with the primary aim of determining the species composition and the level of weed infestation. A total of 457 fields under conventional and 165 under organic production were investigated in late July-early August. Roughly half of the 189 species observed were perennials but the majority were of minor importance in terms of frequency and abundance. However, the problems caused to crop production by the three most abundant perennials, Elymus repens, Cirsium arvense and Sonchus arvensis, are pronounced, particularly in organic cropping with its diverse crop rotation and less intensive weed control. A major challenge facing the continuation of organic spring cereal production in Finland is the need to prevent the proliferation of these weed species.