Weed problems can constrain organic crop production resulting in significant losses in yield and quality. Especially perennial weed species such as Elytrigia repens, Cirsium arvense and Tussilago farfara are posing problems as arable cropping systems do not hamper their vegetative proliferation sufficiently. Annual weeds may also reach unacceptable infestation levels leaving the growers with poor yielding crops and severe future weed problems owing to the shedding and spread of weed seeds. Effective weed management is a key component for successful organic crop production and a prerequisite to increase the yielding potential of many organic crop production systems. Weed problems are most severe on stockless arable farms because the supply of nutrients can be limited and may not suffice to produce competitive crop stands. Crop rotations in arable cropping systems often have fewer grass-clovers leys or other perennial crops known to disrupt weed proliferation more effectively than cash crops such as cereals and pulses. The higher nutritional status of soils on dairy farms and the more frequent use of perennial crops for mowing are major causes for less severe weed problems on those farms
