A type of chemical used to kill plant-parasitic nematodes. Nematicides may be classed as soil fumigants or soil amendments, space fumigants, surface sprays, or dips. Soil treatments are commonly used because most plant-pathogenic species spend part or all of their life cycle in the soil, in or about the roots of plants. Nematicides may be liquids, gases, or solids, but on a field scale, liquids are most practical. These materials possess a high vapor pressure and volatilize quickly to act as soil fumigants. Carbon disulfide, CS₂, and chloropicrin were among the first to be developed for this purpose. Their use is fairly restricted because of high cost; besides, CS₂ is highly flammable and explosive and chloropicrin requires a cover or water seal.