ABSTRACT
Different ways, by which farmers in northern Germany try to minimise their costs and maximise their yields were analysed from the viewpoints of economy and of ecology.
Growing wheat repeatedly can enhance the saddle gall midge, but apparently not the wheat blossom midges. The main limiting factors preventing the permanent growing of wheat in northern Germany are cereal diseases rather than insect pests.
It is shown by comparative studies, that growing wheat at a high level of intensity depresses numbers of beneficial arthropods, favours the cereal aphids, but does not give the best economic profit (though the yield may be best, the costs are too high). Routine insurance sprayings against cereal aphids are shown to be uneconomic. Cereal aphid control should rather be performed according to critical thresholds. Another study revealed that the repeated routine application of insecticides, which is not economic on the one hand, may enhance pest populations in sugar beet on the other. The reduced number of polyphagous predators seems to be responsible for this.
In consequence of the findings presented it is stressed that a lower level of intensity in agriculture is advisable to farmers from the economic view. Furthermore, the antagonists of pests will then be able to act more efficiently in favour of the farmers.
