A survey of weeds in spring-sown oilseed crops (Brassica rapa ssp. oleifera and Brassica napus ssp. oleifera) was conducted in southern and central Finland during 20072009, representing the first such extensive investigation in the country. The occurrence of the most abundant weed species in oilseeds was surveyed in 429 fields. In the fields with moderate or high weed infestation, 16 harmful weed species were recorded by visual observation according to their biomass production. About 40 weed species were recorded, the most predominant being Chenopodium album, Galeopsis spp., Galium spurium, Sonchus arvensis and Tripleurospermum inodorum. Elymus repens was the only major grass weed. Chemical weed control of broad-leaved weeds had been practised in 53% of the fields, resulting in relatively good control. In addition, both selective graminicides and glyphosate were used to control E. repens. Mechanical weed control was not practised in any field. The crop yield level was about 300 kg ha-1 higher in the fields with low weed infestation compared with in the highly infested fields. New promising options to replace the banned herbicide trifluralin are available. Thus, the most harmful weeds, such as C. album, which interferes with the production of high-quality oil for human consumption, can still be effectively controlled.;
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