Weed competes with the crop for light, water and nutrients. Competition for resources can cause crop losses which in some cases can be significant, as well as provide a crop of poorer quality. It is therefore important to develop strategies that keep weeds at a reasonable level. Not keeping the weeds under control can cause major problems with an increasing seed bank in the future crop. The effort of combating weeds varies largely between different crops and a well thought trough strategy in the crop rotation is important. The application applies to 10 series of field trials in weed combating, focusing on blackgrass, poa annua, common windgrass, thistle and annual weeds in crops of winter wheat, barley, peas, flax and winter oilseed rape. Also included is a new series of trials studying the effect of water quality on annual weed combating.