Blight-MOP: Development of a systems approach for the management of late blight (caused by Phytophthora infestans) in EU organic potato production

Blight-MOP Late blight (caused by Phytophthora infestans) is the most devastating fungal disease affecting organic (and conventional) potato production in the EU. It kills the foliage and usually results in losses of yield which can be very large when infection is severe and occurs early in the season. The disease may be transmitted to the tubers which become unmarketable and these can lead to complete deterioration of the stored crop if put into storage with healthy tubers. To a great extent, conventional production systems rely upon frequent applications of synthetic fungicides with different modes of action for late blight control, but this is seldom completely successful. However, in organic systems, the availability of chemical fungicides is currently restricted to those which are ‘considered to be traditional organic farming practices’: these include copper hydroxide, copper oxychloride (tribasic), copper sulphate and cuprous oxide that have a protectant action and are reasonably effective. Their use is restricted by national legislation and organic certifying authorities and pressure has been mounting to withdraw them not only because of possible adverse effects on wildlife, the environment and human health but also their incompatibility with organic production principles. This led to a proposed ban on the use of copper fungicides for control of late blight in organic farming in the EU from March 2002 which had potentially serious implications for the potato crop. The resultant losses of yield and hence income in the absence of copper-based fungicide sprays were expected to threaten the economic viability of both organic potato enterprises and/or whole organic farming businesses in many areas of the EU in the medium to long term until effective, alternative methods are developed. In the meantime, two major approaches were adopted. One was to set a limit to the amount of copperbased fungicides permitted for application: until 31 December 2005, the maximum application was restricted to 8kg of elemental copper/ha/year for annual crops, declining to 6kg/ha/year from 1 January 2006 (but this could be changed at any time in the light of developments in viable alternatives or should there be proposals for withdrawal under the EC Review programme for existing active substances). Another was to promote further research to identify and develop effective alternative late blight control methods and strategies without the undesirable effects associated with copper-based fungicides. The Blight-MOP project – ‘Development of a systems approach for late Blight (caused by Phytophthora infestans) Management in EU Organic Production systems’ was initiated in March 2001 to achieve this aim and maintain yield and quality and hence commercial viability of organic potato crops without the use of copper fungicides. Such an approach involves integrated use of (i) resistant varieties (ii) existing agronomic strategies (iii) alternative treatments that can replace synthetic and copper-based fungicides (iv) use of existing blight forecasting systems to optimise control treatments and to maximise synergistic interactions between (i), (ii), (iii) and (iv). The specific objectives were to: 1. Assess the socio-economic impact of late blight and ‘state-of-the-art’ blight management practices in EU organic potato production systems 2. Assess varietal performance in organic production systems in different EU regions and interactions with local blight populations 3. Develop within field diversification strategies to prevent/delay blight epidemics 4. Optimise agronomic strategies for the management of late blight 5. Develop alternative control treatments to copper-based fungicides that comply with organic farming standards 6. Evaluate novel application and formulation strategies for copper- free/alternative and copper-based late blight treatments 7. Integrate optimised resistance management, diversification, agronomic and alternative control treatment strategies into existing organic potato management systems. To pursue these objectives, experiments were conducted over 4 seasons from 2001 to 2004 under organic cropping system conditions in seven countries (Denmark, France, Germany, Netherlands, Norway, Switzerland and United Kingdom) spanning a wide range of aerial, soil, production and marketing environments. The rate and severity of the late blight epidemics in 2001, 2002 and 2004 gave a rigorous test of the different components of the integrated management system which gave broadly similar effects in the three years. In 2003, the very hot, dry summer (and August in particular) severely restricted the disease making it difficult to evaluate the efficacy of treatments in some regions, but in others where infection did occur the general trends were similar to those observed in other years.