From laboratory to field: Copper-free preparations for organic potato production

As of yet, effective direct control of potato late blight in organic potato production requires the application of copper fungicides. However, with common dosage, copper is ecologically harmful. Hence, a considerable reduction or replacement of copper compounds in disease control is desirable. In the framework of the EU-project Blight-MOP comprising a systems approach to manage late blight in organic potato production without copper, 53 commercialised and experimental copper-free preparations were evaluated for their potential to control the disease by means of laboratory, greenhouse and field trials. Additionally, the potential to reduce copper fungicide input through optimised timing using the decision support system Bio-PhytoPRE developed at ART was assessed. In the laboratory, one-third of the copper-free preparations completely inhibited germination of sporangia and one-forth that of mycelial growth of Phytophthora infestans. In the greenhouse experiment one fifth of the copper-free preparations reduced foliar blight of tomato plants by at least 80 %. In microplot field trials, several copper-free preparations significantly reduced foliar blight of potatoes compared with the untreated control. However, the efficacy of the copper fungicides was never obtained. In small-plot field trials using practice-like application strategies, none of the copper-free preparations adequately controlled late blight sufficiently. The poor performance of the copper-free preparations under field conditions could be attributed to their low persistence and their lack of rain fastness compared to copper fungicides. In contrast to copper replacement, the strategy of using reduced application rates of copper fungicides according to the decision support system Bio-PhytoPRE proved to be successful.