Copper reducing strategies for late blight (Phytophthora infestans) control in organic potato (Solanum tuberosum) production

摘要

In organic potato (Solanum tuberosum) production in Europe, solely copper-based fungicides allow to directly control late blight (caused by Phytophthora infestans). Due to environmental concerns, the use of copper (Cu) fungicides has to be as efficiently as possible to reduce annual consumption. This can be achieved either by reducing the dose per application or by decreasing the numbers of sprays. Between 2005 to 2009, six field trials were conducted at two sites (3 each) in northern Germany in order to (a) determine the efficacy of a copper fungicide (copper hydroxide) at reduced rates compared to the common practise of the most important German organic farmers' associations (3 kg Cu ha(-1)), and (b) to evaluate the copper reduction potential of an application strategy based on a decision support system (DSS). A clear dose-response relationship with reduced rates of copper hydroxide was not consistent over trials and strategies although there was clear evidence for a considerable potential to reduce Cu rates compared to the amount of 3 kg Cu ha(-1). However, different degrees of late blight pressure strongly affected the efficacy of the Cu fungicide in individual years. Under less late blight pressure, a reduction to 1.25 kg Cu ha(-1) applied throughout the season was possible without significant loss in efficacy compared to the typical spraying of 2.5 or 3.0 kg Cu ha(-1). Due to a higher risk of decreasing efficacy, reducing Cu hydroxide supply was only possible to an amount of 2.0-2.5 kg Cu ha(-1) under moderate disease pressure while high late blight pressure in 2007 did not allow a Cu reduction to this extent. Even the highest amount of 3.0 kg Cu ha(-1) only decreased the disease by 18% in one single case. Consequently, yields were not consistent, but depended on year, site and late blight pressure. On average over rates and strategies, Cu application increased yields by 15%. In addition, the results revealed the clear tendency that reducing Cu amounts did not impair tuber yield. A spray schedule based on the new German DSS OKOSIMPHYT increased effectiveness of Cu sprays, reduced numbers of sprays and the total amount of Cu per year, even under moderate and high late blight pressure. Therefore, we conclude that the DSS has the potential for further optimization. Knowledge of actual late blight pressure, as provided by OKOSIMPHYT, is necessary to optimize the use of Cu fungicides allowing both to ensure the site-specific tuber yield potential and to reduce the CU application amounts.