False cleavers (Galium spurium L.) sown within a week of rapeseed (Brassica campestris L.) competed with the crop and contaminated the crop seed even when infestation was light. Competition by an infestation of 100 false cleavers m−2 throughout the growing season reduced rapeseed yield by 18%. Trifluralin and ethalfluralin controlled 80–90% of false cleavers, but survivors produced sufficient seeds to contaminate the crop. Selectivity and 85% control were achieved with benazolin amine at 0.5 kg ha−1, but the EC formulation injured the crop.Key words: Galium spurium L., rapeseed, competition, control