Herbicides are often used before planting to help clear a cover crop or weeds, and after planting, e.g. when used in conjunction with safeners or herbicide-tolerant crops. Herbicide, an agent, usually chemical, for killing or inhibiting the growth of unwanted plants. Herbicides are a broad class of pesticides that are used to remove nuisance plants, such as grasses and weeds, that may compromise the growth and yield of desired crops that are in close proximity.