Fumigants and Nematicides

Abstract

It has been estimated that plant-parasitic nematodes are as important economically as fungi, bacteria, or viruses. Nematodes distribute about 0.3 m below the soil surface. Meloidogyne, Heterodera, Tylenchulus, Rotylenchulus, and Protylenchulus are important agricultural pest nematodes. To be effective, chemicals must have high volatility at room temperature. Hence, nematicides are generally gases or volatile liquids of comparatively low molecular weight enabling them to penetrate through soils. Nonvolatile nematicides diffuse in soil by watering or mixing in soil. Fumigation is an important method of soil sterilization for the control of soil insects, nematodes, fungi, and weed seeds. It is also very important in the control of stored product insects and fungi provided that the fumigants do not leave toxic residues on the fumigated commodities. Chemical fumigants, because of their high volatility, must be used in enclosed spaces such as greenhouses, food stores, warehouses, and the like. For soil treatment, the surface of the soil must first be covered with a plastic sheet to prevent loss of the fumigant. One of the earliest fumigants used commercially probably was hydrogen cyanide which was used for the control of scale insects on citrus trees in California.