The following four chapters consider the selectivity of pesticides in relation to their mechanisms of action. Compounds are generally grouped according to their mode of action, and in some cases this coincides with the chemical family to which they belong, such as the organophosphate and carbamate insecticides, benzimidazole fungicides and auxin-type herbicides. Both the chemical structure and a representative trade name are given. This does not constitute a recommendation but hopefully serves to link product names known by farmers, growers and agronomists to the active ingredients that they contain. In general, trade names current in the UK at the time of publication of this book are used, but many of these product names have been adopted more widely by manufacturers. The dose rates given are derived from appropriate product manuals, and refer to the range of maximum doses permitted for the product, again at the time of publication of this book
It is important to note that many pesticides are used in combination to extend the spectrum of activity of the product, and in some cases to cope with problems of pest, weed or pathogen resistance. However, the amount of active ingredient in mixtures rarely, if ever, exceeds the dose recommended for compounds used on their own. In figures of pesticide structure, numbers in parentheses after the dose rate indicate whether more than one application of a pesticide is permitted, and give the maximum number of applications allowed in a year or growing season. Such multiple applications apply mainly to fungicides and insecticides.