Data on the efficacy and crop safety of plant protection products can be used for registration purposes in other countries, provided crop growth conditions are comparable. This article identifies the main conditions which are relevant in this respect, with particular emphasis on climatic conditions. Comparison of several systems of agro‐climatic classification developed for the EPPO region, particularly the climate diagrams of Walter & Lieth, the climate classification system of Köppen & Geiger, the agro‐climatic areas of Thran & Broekhuizen and natural vegetation maps, has led to a division of the EPPO region (Europe, Mediterranean area, Middle East) into four agro‐climatic zones (Mediterranean, Maritime, North‐east, Central) within which conditions can be considered comparable.
Fungicide inputs in cereals have to be reduced, in order to sustain gross margins and reduce environmental side effects. This can be achieved by using fungicide programmes in which doses and timing of fungicides are influenced by detailed knowledge on inherent properties of the fungicides, cultivar resistance and epidemic development of diseases in relation to crop stage and weather conditions. In 1994 and 1995, field trials were carried out in winter wheat in which strategies using full and reduced rates at fixed growth stages were compared with the computerized weather‐based decision support systems PC Plant Protection and PRO_PLANT. A further strategy was included in which timing and dosage of fungicides was based on expert judgement of the interactions of growth stage, disease pressure, weather conditions and cultivar resistance. Effective control of septoria diseases, brown rust and powdery mildew was achieved by all programmes. There was no programme that always resulted in the highest yield and gross margin.
Weather circumstances before, during and after the application of plant protection products are very important for efficacy. Knowledge of the behaviour of products in relation to weather circumstances can be an aid to achieving better efficacy and even serve as a tool for reducing the dose in well-defined applications. Formulation type and dynamic build-up of the wax layer on the upper side of the leaf are important for sticking and the speed and method of uptake of active substances into the leaves. It is difficult for farmers to combine all the important processes. Knowledge of the relations between plant protection products and meteorological conditions is combined in a decision support system (DSS) with the acronym GEWIS. The system calculates (hourly based) the physical behaviour of products at different stages in the process. With the help of this DSS, the farmer can choose the best moment of the day to apply a product with the optimum dose. Furthermore, users learn when it is possible to apply lower dosages and when not to apply at all.
Initiatives such as Videotext and forecasting models resulted in a relatively fast introduction of computer technology on to farms at the end of the 1980s. In several countries there were developments to create models for supervised control and data exchange became digital. Most models were developed for diseases that could expand very rapidly, or diseases that should be controlled regularly. In the 1990s, development of weather‐related Decision Support Systems (DSSs) began. It is important to use the optimal way to disseminate information to the target group; which can differ between or even within countries. The use of DSSs results in a lower risk of crop damage by diseases and pests, and a lower input of active substances, from the use of adjusted dosages. Future developments may include the possibility of implementing a number of DSS‐models into a Geographical Information System, which will support precision agriculture by providing adjusted spraying advice based on plot‐specific characteristics. The success of DSSs is despite its development occurring independently in a number of countries. The speed of development of these systems would have been substantially faster had there been real cooperation between countries or groups of researchers. In order to withstand funding reductions, it is necessary for the development of new DSSs that collaboration between researchers and research groups internationally increases significantly in the near future.
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