Diversität, Pflanzenernährung und Prognose: Ein integriertes Konzept zum Management der Kraut-und Knollenfäule in der Ökologischen Landwirtschaft

In organic potato production adequate plant nutrition and plant protection have to be achieved by long term and preventive management strategies. Late blight, caused by Phytophthora infestans Mont. De Bary is one of the most important diseases in organic potatoes and besides varietal resistance its management in Germany relies mainly on the limited use of protective copper based fungicides. The currently allowed amounts of copper of 3?kg?ha^?1 and year are more than necessary for plant nutrition and thus are in contrast to the aim of sustainability of organic farming. The results of the presented studies show that it is usually possible to achieve good disease control with only 1–1.5?kg?Cu?ha^?1 even under high disease pressure with the help of the forecasting model BioPhyto-PRE which was developed for organic farming. To increase the efficiency of less effective fungicides such as plant extracts in organic farming, disease pressure has to be reduced as much as possible by management approaches. Four on-farm experiments showed that strip intercropping of potatoes does reduce disease pressure in 12–16?m wide strips with neighbour spring wheat or carrots. A cost-benefit analysis using the prices of the year 2004 showed that growing potatoes without treatment in most cases was the most lucrative option with slightly increased benefits by strip cropping the potatoes. Multiple stepwise regressions show that in organic farming the yield loss relationships between late blight and potatoes can only be determined when N-uptake is integrated into the model. Overall, only very limited yield benefits are achieved by the application of copper fungicides, in most cases due to the limited nutrient supply in organic systems. It is concluded that an integrated forecasting model for late blight management in organic farming will have to include data on growth stage dependent plant nutrient uptake and variety specific properties to allow for efficient and minimised fungicide applications.