Institute for Plant Diseases, University of Bonn, Nussallee 9, D-53115 Bonn, Germany

Background and objectives
Agricultural production is currently characterized by high-input systems with high productivity and surplus production in developed countries, and by low-input systems, production deficits and malnourishment in many developing countries. Production of food and feed is limited due to limitations in natural resources, the genetically determined productivity of crops, the ability of man to maintain or replenish these resources, and shortcomings of protecting crops against pests. Farmers have to cope with competition from other organisms which are favoured by the uniformity and repeated cultivation of susceptible crops, endangering productivity. In order to promote crop growth and yield, farmers have to protect plants against pests, organisms damaging crops grown for human requirements. The incidence and intensity of pests differ between crops and regions depending on the climatic conditions, the susceptibility of crops, and the cultivation techniques including fertilization, water supply and crop protection. The impact of actual crop protection measures on crop productivity in different regions has been calculated from the loss potential of diseases, animal pests and weeds (no control scenario), and the actual losses despite current crop protection measures for the most important food and cash crops. The yield effect of pesticides has been calculated in scenario studies considering changes in the cultivation of crops without the use of pesticides [1].

Results and conclusions
The loss potential of pathogens, animal pests and weeds, and the actual crop losses in wheat, rice, maize, barley, potato, soyabean, cotton and sugar beet, have been estimated by evaluating data from literature and field experiments. Total losses were calculated from yield reductions on a regional and global level. Since 1965 [2], worldwide production of most crops has increased considerably. Simultaneously, crop losses in wheat, potatoes, barley and rice increased by 4-10%, whereas in maize, soyabean and cotton losses remained unchanged or slightly decreased. The efficacy of crop protection practices was calculated as the percentage of the loss potential prevented by control measures. The efficacy is highest in cotton (55%), and reaches only 34-38% in the food crops rice, wheat and maize. The variability among cropping areas is high.. In western Europe, 61% of potential crop losses are prevented; in North America and Oceania, 44%; and in all other regions, 38%.

Scenario studies on the impact of a ban of pesticides in the EU reveal different implications for farming systems of high and moderate productivity. The higher the potential of crop productivity, often the higher the susceptibility of crops to yield reductions due to pests, and the higher the cost effectiveness of crop protection measures. Therefore a ban on pesticides, especially fungicides and insecticides, would cause considerably higher yield reductions in field crops in northern Europe, with currently very intensive farming systems, than in southern Europe, where productivity per area is lower. In view of population growth and rising food demand, crop production has to be increased substantially [3]. As potential loss rates often increase with attainable yields, high productivity largely depends on effective crop protection management. Recent and future developments in crop protection can contribute to establishing sustainability in agriculture and to preserving natural resources. However, although effective control methods have been developed for most biotic yield constraints, the use of crop protection products is regulated by economic considerations rather than by food demand.

1. Oerke E-C, Dehne H-W, Schoenbeck F, Weber A, 1994. Crop Production and Crop Protection - Estimated Losses in Major Food and Cash Crops. Elsevier Science, Amsterdam.
2. Cramer HH, 1967. Pflanzenschutz und Welternte. Bayer Pflanzenschutznachrichten 11.
3. Alexandratos N (ed.), 1995. World Agriculture: Towards 2010. An FAO Study. FAO, Rome/Wiley, Chichester, New York.