Herbicides are chemicals used to manipulate or control undesirable vegetation. Herbicide application occurs most frequently in row-crop farming, where they are applied before or during planting to maximize crop productivity by minimizing other vegetation.
It is usually a chemical, for killing or inhibiting the growth of unwanted plants, such as residential or agricultural weeds and invasive species. A great advantage of chemical herbicides over mechanical weed control is the ease of application, which often saves on the cost of labor.
Herbicides are divided into numerous categories:
1. Selective (affecting specific plant species).
2. Nonselective (affecting plants generally). can be used to clear waste ground.
3. Foliage-applied: A. Contact herbicides that kill only the plant organs with which they are in contact. B. Translocated herbicides (systemic) effective against roots or other organs to which they are transported from aboveground treated surfaces.
4. Soil herbicides: A. Preemergence: prevents weed seedlings emerge. Sprayed on bare soil. Usually, activated by rain or irrigation. B. Absorbed by the roots and translocated to the leaves.
Weed resistance to herbicides has become a major concern in crop production worldwide. Resistance to herbicides is often attributed to lack of rotational programs of herbicides.