Crop competition frequently is the most effective and economical weed control practice available, yet this contribution usually goes unrecognized and seldom is considered when a weed control program is planned and developed. Shading is the major factor by which crops suppress weeds. Any factor that hastens shading by the crop will enhance its competitive ability. Supplemental weed control is needed most at those times when the crop does not produce full shading. Crops can be managed to provide maximum shading.
Crop rotation is feasible for annual, biennial, or short-term perennial crops.
It is not available for long-term established perennials crops. The more dissimilar the crops and their management practices are in the rotation system, the less opportunity an individual weed has to become dominant. A practical substitute for crop rotation is to employ varying weed control practices as much as possible. The allelopathic properties of cover crops such as rye and plant residues such as wheat stubble can provide effective weed control in some crops. Larvae of the cinnabar moth feed on foliage and flowers.