Mechanical control can involve several different methods. Burial, by which all growing plants are buried under the soil surface, is most effective on annual weeds. It is less effective on perennial weeds, which have underground root systems and are capable of regrowth. However, care should be taken because deep cultivation can damage crop roots. Deep cultivation may also pull more weed seeds to the soil surface where they will germinate.
Crop rotation is yet another method.
If the same crop is planted in the same field year after year, weeds will appear that have become tolerant of the cultural practices and herbicides used on the crop. By rotating to other crops, the types of cultural practices and herbicides will change, thus not allowing weeds to become adapted to any particular regimen. Chemical control is flexible in that it can be administered preplanting, pre-emergence and postemergence. Application can be broadcast, band, directed, or spot treatment, depending on weed type, severity of infestation, and location. Biological control has not been used as a weed control agent to a great degree, but that may be changing.