The registration process is comprehensive and includes a review of the toxicology of the product, a demonstration that the product is effective for the pest for which it is intended, and the nature of the treatment needed to control the problem. Registration and Useīecause pesticides are toxic, their use is carefully controlled and, in Canada, pesticides may be sold only after they have been registered by Agriculture Canada. Through genetic engineering, it has been possible to produce plants which synthesize their own insecticides and are thus protected from insects. New pesticides now under development will likely be of biological origins. ![]() Over time, target species develop resistance to specific pesticides and dosages have to be increased or new pesticides developed. ![]() With the exception of mercury, most of the fungicides are not very toxic to warm-blooded animals because they are toxic to systems in fungi that are quite different from those found in mammals and birds. Some newer classes of insecticides have been developed that act on processes found in insects but not in mammals, eg, compounds that interfere with the molting process in insects or that affect hardening of the cuticle. Many insecticides act on the nervous system of insects and, although less toxic to warm-blooded animals, act on the nervous system of these organisms as well. In general, insecticides are more toxic to warm-blooded animals than herbicides or fungicides, but some of the older fungicides, such as mercury and the arsenite herbicides, are also highly toxic to mammals and birds. The nature of the toxicity of pesticides differs between different classes of substances. Within a class of compounds, however, toxicity varies widely, from 10 or fewer milligrams per kilogram to several thousand mg/kg. Many pesticides are selective in their toxicity, being highly toxic to some organisms and much less so to others. Other tests include studies on the environmental fate of the chemicals and effects on wildlife and other non-target organisms. These tests include those for carcinogenicity (tumour formation), teratogenicity (birth defects) and mutagenicity (genetic damage). Modern pesticides are tested for a wide variety of toxic effects before they may be used. The RAT is the most common mammal used for determining LD50 values but the MOUSE and the RABBIT are also usually tested. The term LD50, used to indicate lethal toxicity, refers to the dosage of the pesticide (expressed as milligrams per kilogram of body weight) required to kill 50% of a test population. Pesticides now available differ widely in their toxicity to different forms of life. After WWII, many synthetic compounds became available, the first of these being DDT for insect control, the phenoxy herbicides (eg, 2-4-D) for weed control, and captan and a series of dithiocarbamates for control of fungal diseases of plants. Relatively few pesticides existed before WWII: insecticides were primarily salts of arsenic, or fluorine or plant-derived products such as nicotine, pyrethrum and rotenone fungicides were primarily based on mercury, copper or sulphur herbicides included petroleum oils, sulphuric acid, some arsenites and salt. ![]() ![]() Pesticides include a wide range of synthetic and natural substances. More than 400 pesticides are now registered for use in Canada they are formulated as liquids, dusts, wettable powders, aerosols and granules. Insecticides, fungicides and herbicides are the most widely used. Substances used to control pests include insecticides (for control of insects), fungicides (for disease-causing fungi), herbicides (for weeds), rodenticides (for rodents), avicides (for birds), piscicides (for fish) and nematicides (for nematodes).
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