11.1. Importance of Selective Pesticides in IPM Programmes The success of released or naturally occurring biological control agents in preventing pest outbreaks in protected crops has led the greenhouse industry to be particularly conscious of the necessity of applying selective pesticides. The activity of a selective pesticide is confined to a narrow range of specific pests (Heitefus, 1975). In IPM, the process of developing the selectivity of a pesticide aims to maximize its specific effect against pests and diseases and minimize its effect on non-target organisms (Hull and Beers, 1985). Thus the selectivity of a pesticide is often used to express its harmlessness for beneficial organisms. The selectivity of the action and of the toxicity of a pesticide is dependent on its physiological selectivity and/or on the application procedures (Poehling, 1989). Physiological selectivity is expressed by reduced sensitivity of an organism to the pesticide due to pesticide metabolism and to the availability of the appropriate enzymes in the target organisms (Hassall, 1982). Application procedures comprise the dose rate, mode of action, method and timing. The use of chemical pesticides that cause undesired side effects on non-target beneficial organisms may lead to pest outbreaks. In tomatoes, multiple application of the broad-spectrum carbamate methomyl for the control of leafminer infestation (Liriomyza sativae Blanchard) eliminated the naturally occurring beneficial parasitoid complex, which, without chemical treatment, reduced the pest population to 50% of the level found in pesticide-treated plots (Oatman and Kennedy, 1976). To avoid these consequences the harmful effects of pesticides on the natural enemies of target pests must be avoided or minimized for successful implementation of biological control agents within IPM strategies. Some pests and pathogens have developed resistance towards certain chemical pesticides, and this must also be considered in order to prevent misuse of pesticides. In this chapter we will deal with the selectivity of pesticides in relation to effects on beneficial organisms that can be used in greenhouses, the potential for improving applications for better performance and selectivity, and the problems of resistance of the pests or diseases to the chemicals used in greenhouses.

Harry Frankel passed away on November 17, 1994, after a long and heroic struggle against cancer, shortly after the death of his wife