The philosophy of 'forewarned is forearmed' whereby pest and pathogen invasion is anticipated and crops monitored for the first signs of their arrival is not new, but the application of new technologies makes it more efficient and effective. Monitoring Brassica crops helps to ensure that control measures, particularly where chemical methods remain available, are applied swiftly and effectively, and as part of the integrated strategy. This contrasts with the previous practices whereby chemical control measures were either applied at specified and regular intervals during the growing season irrespective of the presence or absence of a particular pest or pathogen or they were used as 'fire brigade' tactics once an outbreak had reached visibly damaging proportions.
In the former case, pesticides were often used in excess of their requirement, resulting in financially costly, wasted applications and environmental pollution as, for example, with powdery mildew (Erysiphe cruciferarum) on Brussels sprouts where little is known about the threshold values for spray control and chemical application is advocated as soon as symptoms appear in August or early September. With the 'fire brigade' approach to control, applications were made when damage had reached the level of visual symptoms and the attendant reduction to quality of the product was probably beyond repair. Again expensive chemicals were wasted accompanied by increased environmental pollution. The essence of integrated control lies in the combined use of genetically resistant cultivars, husbandry and nutritional strategies (Chapters 2, 4 and 5) that decrease the likelihood of pest and pathogen outbreaks and minimal use of pesticides applied on the basis that an outbreak is predictable in its occurrence. Components that can form elements in the integrated control strategies for either pests or pathogens were summarized by S. Finch (personal communication) under two headings: (i) well established methods such as: insecticides, forecasting, supervised control, cultural control and physical control; and (ii) experimental systems still being developed such as: undersowing, parasitoids, predators, parasitic viruses and bacteria, parasitic fungi and nematodes, and behaviour-modifying chemicals.
Each of these components is considered at various points in the chapters of this book.
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