Pesticides may be useful when non-chemical methods fail to provide adequate control of pests and when pest populations reach a level of economic injury. The suffix "cide" literally means kill. The term pesticide refers to a chemical substance that will kill pests. Since it is physically impossible to eradicate an entire population of pests, pesticides are used as a tool to control or manage pest populations to a level of tolerance. Because of government regulations, chemicals used to attract or repel pests and to regulate plant growth or function are also classed as pesticides.