A pesticide is any substance or mixture of substances intended to prevent, destroy, repel or reduce the effects of pests. Pests can include insects, weeds, birds, mammals, fish, plant pathogens and microbes that compete with humans for food, destroy property or spread disease.
Pesticides are generally classified by the specific type of pest they target. Insecticides target and eliminate insects and other arthropods. Herbicides target and destroy weeds and other unwanted vegetation. Fungicides target and kill fungi. Rodenticides are used to control rats, mice and other rodents. Larvicides target mosquito and other insect larvae before they mature. Bactericides destroy bacteria.
Pesticides can also be categorized by their origin and composition. Biopesticides are derived from natural materials such as plants, bacteria and certain minerals. Synthetic chemical pesticides (such as the widely used herbicide glyphosate) are human-made chemicals designed to disrupt a pest's nervous system, growth or reproductive cycles.