WEED ECONOMIC THRESHOLDS IN CEREALS IN THE FEDERAL-REPUBLIC-OF-GERMANY

The determination of fixed guide values for weed economic threshold in cereals is briefly reviewed. A 2-year experimental series in winter cereals to validate these threshold values in the Federal Republic of Germany is described. It was found that the use of fixed threshold values to decide when to control annual weeds was more profitable than prophylactic herbicide application. The fixed threshold values are 20-30 plants m-2 for grass weeds, broad-leaved weeds 40-50 plants m-2, Galium aparine 0.1-0.5 plants m-2 and Fallopia convolvulus 2.0 plants m-2. Alternatively, broad-leaved weeds have to be assessed as percentage ground cover, 5-10% being the threshold. In order to improve further the predictions from the economic thresholds a more flexible computer-based decision model has been developed. This includes updated biological data and simple economic calculations. Further experiments have been done to validate the model. Assessments based on the calculated net return indicate that weed control decisions were slightly improved by model recommendations compared with the fixed threshold concept. The basic assumptions in the decision model are discussed and possibilities for future applications under practical conditions are described. © 1990.