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Blight - MOP
Development of a systems approach for the management of late blight in EU organic potato production

Potato late blight causes substantial economic losses in organic production systems throughout the European Union. This means that the ban on copper fungicides will substantially increase farmers' losses, unless suitable alternative blight management strategies are developed. Potato is a major cash crop for many European organic farming businesses. Compared to conventional production yields, organic production yields are estimated to be between 30-40 % lower, even when copper is used to delay blight development in crops. Copper fungicides are estimated to extend the growing period (before the potato foliage has to be destroyed to prevent the spread of blight to the tubers and neighbouring fields) by between 2-4 weeks. This is estimated to result in between 10 and 40% higher yields compared to crops not protected by copper (in which the foliage has to be destroyed earlier). Yield reductions of between 10 and 20% resulting from the ban on copper fungicides could threaten the profitability of organic potato production and/or the entire organic farming businesses in many EU-countries.
The proposed project aims to develop improved organic production systems in which potato blight can be managed without any - or with minimum - alternative treatments. This will be achieved by developing regionally adapted, blight management strategies based on the identification of best current practice in different regions of the EU; variety resistance management; field diversification strategies; preventative agronomy and the development of improved formulation/application technology for alternative treatments to copper fungicides.

The overall aim of this project is to develop a systems approach for the control of potato late blight (caused by Phytophthora infestans) in a way that allows the commercially viable production of organic potato crops without the use of copper fungicides.
The quantitative target is, therefore, to maintain potato yields and quality at levels currently obtained with the use of copper fungicides. An important aspect of the project will be the rapid dissemination of results and the adaptation of strategies to local potato management systems.
To achieve this overall aim, the following individual project objectives will be achieved:
1) assessment of the socio-economic impact of late blight and state-of-the-art blight management practices in EU organic potato production systems
2) assessment of varietal performance in organic production systems in different EU regions and interactions with local blight populations
3) development of 'in-field diversification' strategies to prevent/delay blight epidemics
4) optimisation of agronomic strategies for the management of late blight
5) the development of alternative control treatments to copper fungicides that comply with organic farming standards
6) evaluation of novel application and formulation strategies for copper-free alternative and copper-based late blight treatments
7) integration of optimised resistance management, diversification, agronomic and treatment strategies into existing organic potato management systems.

The rate and severity of the late blight epidemics 2001 and 2002 gave a rigorous test of the different components of the integrated system. In general, effects of the individual components were very similar in both years. In 2003, very hot and dry conditions prevailed in summer across the EU (particularly in August) which severely restricted blight epidemics. In some cases, it was not possible to evaluate the efficacy of treatments for late blight control because of low levels of infection. However, in others, where infection did occur the general trends were similar to those observed in 2001 and 2002.
'State of the art' blight management surveys
There are large regional differences in the impact of late blight on organic potato production in the EU. Farmers use a high diversity of strategies to stabilise yields and income, but not all use available technology. There is a widespread view that a copper fungicide ban will have serious consequences for organic potato production unless effective alternatives are available.
Variety performance
Resistant varieties consistently gave most effective prevention of foliage and tuber blight compared with diversification and agronomic strategies and alternative treatments to copper fungicides. However, yields of resistant varieties were not necessarily higher than more susceptible varieties although they would decrease the source of inoculum. Copper fungicides gave limited benefit in resistant varieties. Acceptability of varieties is determined more by market demands than blight resistance.
Diversification strategies
Usefulness of mixtures of potato varieties for reducing the impact of blight depended on the level of resistance of varieties in combination, but in some cases, yield was improved where ecological interactions were improved. Alternating rows of susceptible and resistant varieties had a relatively small impact. Intercropping potatoes with grass/clover or spring wheat reduced blight in small plots grown perpendicular to the wind but yields were unaffected. Wheat was more effective at reducing blight than either grass/clover or potatoes, but yields were decreased because of competitive effects and there would be practical difficulties with such an approach. Such approaches may be useful as part of a combined control strategy.
Agronomic strategies
Plant population and spacing had no effect on blight but total and graded yields were affected. Effects of planting date and chitting on blight were small and insignificant but had marked effects on total and graded yields in 2001 and 2002 (but not 2003 because of premature senescence). Defoliation mechanically and/or by heat treatment decreased the number of blight sporangia per plant but had no effect on tuber blight. Blight was unaffected by manurial treatments or N:K ratio, but fertility management influenced yield. Potatoes grown after grass/clover or Lucerne were more infected with blight than after spring wheat but yield was not affected because of improved fertility. Pigs effectively removed groundkeeper potatoes post-harvest and hence the potential problem of volunteers as a source of blight inoculum but caused soil compaction and establishment problems in the subsequent cereal crop.
Alternative treatments
Extracts of manure-based composts gave control of blight in potato leaf assays but not in the field. However, use of an adjuvant in combination with an autoclaved compost extract gave improved control and slightly higher yields in an experiment in 2003. Some micro-organisms, plant extracts and existing products showed promising effects on blight control. Efficacy of a range of commercial and novel anti-fungal compounds was unaffected by dose rate or formulation. Copper free compounds had either no or limited effects on blight compared with standard copper fungicides at normal rates but low doses of copper products were almost as effective.


Scientist responsible for the project

Nafferton Centre for Organic Agriculture, Nafferton Farm
NE43 7XD Stocksfield Northumberland
United Kingdom (The) - GB

Phone: +44 1661 830222
Fax: +44 1661 831006


Project ID QLRT-1999-31065
Organisation University of Newcastle, Tesco Centre for Organic Agriculture
Area 5.1.1
Start date 01 March 2001
Duration (months) 54
Total cost 6 064 258 €
Total EC contribution   3 832 614 €
Status Completed

The partners

  • Norsk Senter for Oekologisk Landbruck (Norwegian Centre for Ecological Agriculture), Norway - NO
  • Groupe de Recherche en Agriculture Biologique, France - FR

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