Institute of Plant Pathology, University of Kiel, Kiel, Germany

Background and objectives
Integrated pest management is a concept which goes well with all economical, ecological and toxicological defence methods, in order to keep pathogens below a threshold of economic damage. The conscious use of natural limits (e.g. the choice of a resistant variety, a restrained use of nitrogen fertilizers, a balanced crop rotation, sowing time, sowing density) is of prime importance and the use of chemical products is limited to necessities. The integrated pest management system, the IPM wheat model, consists of diagnostic elements, (qualitative = pathogen, quantitative = disease severity), and control thresholds (pathogen-specific thresholds in the pathogen population which define the optimum time for a fungicide). The pathogen-specific control thresholds (eye spot, tan spot, glume and leaf blotch, powdery mildew, yellow and brown rust) are based on many years' nationwide studies of epidemic and damage dynamics, which depend on weather, cropping system and level of inoculum.

Materials and methods
The IPM wheat model has been evolved in order to control pathogens at a time when it is possible to achieve optimal biological effects for the development of the disease by using as little chemical input as possible, and to achieve the best economical and ecological results. In all cases, the results of using the threshold concept (diagnosis - control thresholds - reduced need of fungicide) document studies on optimal biological and economical control of the epidemic compared with inflexible stage-oriented routine measures.

Results and conclusions
The epidemic-orientated procedure led, within averages of the years, to a 50% reduced application frequency and to a 66% reduction of fungicides on each hectare, in comparison to stage-oriented measures (stage-oriented 1405 g a.i./ha; IPM 530 g a.i./ha). According to the IPM wheat model, the economic benefit was increased by almost 100%. With the development of the IPM wheat model, it has for the first time become possible to combine crop protection measures against important foot, leaf and ear diseases according to defined criteria in such a way that the legal requirements for integrated crop management can be complied with all the way to practical agriculture. The IPM wheat model is a part of the official advisory services in different regions of Germany. Results of epidemic case studies have been demonstrated as well as biological, economical and ecological effects.

1. Vereet JA, 1995. Principles of Integrated Pest Management, The IPM Wheat Model. Pflanzenschutz-Nachrichten Bayer.
2. Vereet JA, Schoefl UA, Morris DB, 1994. Proceeedings of the Brighton Crop Protection Conference: Pests and Diseases, pp. 671-678.