Introduction

Background to the Blight-MOP research project

Late blight is the most serious disease affecting potato production in Europe. It spreads rapidly and can devastate an entire crop.
The Blight-MOP project was launched in March 2001 to develop a comprehensive approach for the management of late blight in organic potato production across Europe. This was largely in response to the proposed complete ban of copper-based fungicides – up till then the most effective way of treating late blight in crops grown according to organic standards. The project ran for four years.

Aims of the project

The first task of the Blight-MOP study was to establish what the state of organic potato production in the EU was, which anti-blight strategies organic farmers were using and how effective they were. In view of the proposed ban on copper, they specifically wanted to find out to which extent copper sprays were used and what impact a complete ban would have on yields in particular and on the viability of organic potato farming in general.
The most important objective of the project was to test how other methods and treatments could be combined to develop an optimal system for the control of blight. Factors like regional climate, variety of potato, soil management and crop protection strategies were studied.  

How did the researchers conduct their work?

Researchers from various universities, research centres and agricultural institutes worked in seven different countries:  Denmark, the Netherlands, Germany, France, Great Britain, Norway and Switzerland. To collect information they interviewed farmers and other experts. Scientists from the thirteen participating research institutes also conducted their own field experiments at various agriculture centres or on established organic farms across the seven participating countries.
Amongst the 118 farmers interviewed, some were organic farmers, others biodynamic farmers. They came from different regions within the different countries. Although participants were chosen for variation in their exposure to organic farming, their farms should have been certified organic for at least two years. Levels of success in organic potato production were measured in two ways, i.e. by looking at gross yield (t/ha) only, or by looking at yield plus efficient use of nutrients plus profitability. Data for the five previous years was used. 
Farmers were asked about conditions on their farms, the techniques they used, business practices, their level of education and experience, their motivations for farming organically, market issues and socio-political matters.

Field experiments involved comparisons between different varieties, different agronomic strategies and different alternative treatments on experimental farms or existing organic certified farms.

What were the findings and conclusions of the initial investigation?

Growth in organic potato production:  In all participating countries, the area of organic potato production had grown between 1998 and 2000. This was not the case for conventional potato production. There were, however, great variations between countries in the area increase for organic potato production. The area growth for production of organic potatoes was still smaller than that for other organic crops. Further expansion of organic potato production was considered likely, but profitability was expected to decrease.
Yield: There was a large difference between countries in terms of organic potato yield, as well as between different farms in one region. Conventional potato yields were higher than organic yields in all participating countries, except Norway.  In the other six countries, organic yield was between 50 and 80 percent of conventional yield. Some organic farmers could improve efficiency and yield by adopting existing strategies.
Varieties used: Organic growers did not grow as wide a range of varieties as conventional growers, and chose cultivars for robustness and acceptance on the market.
Price: Farm gate prices were higher for organic potatoes than for conventional potatoes, but varied from country to country.
Consumer preferences: In deciding which organic product to buy, consumers rated production practices highest, then price, variety and taste. Processors looked for process quality and variety in organic potatoes.
Farmers’ opinions: There were differences of opinion amongst farmers regarding the profitability of the industry. Most farmers were primarily motivated by environmental factors, food quality and other philosophical considerations. 
Effects of blight: Outbreaks of blight between 1996 and 2000 varied greatly from region to region. In some countries not all farmers had losses while in others more than 70% of farmers had losses with every outbreak.
Defoliation: In the Netherlands foliage had to be destroyed at 5% infection stage as this was a statutory requirement.
Copper fungicides: The use of copper-based sprays varied greatly from country to country, largely according to variations in legal stipulations. In Scandinavian countries it was not allowed at all, in some countries it was limited, in some not limited until 2001. EU limitations were then set at 8kg/ha/year. Where farmers could use copper, they generally did. Some also tried alternative products, but with little success. A ban on copper-based fungicides while there are no effective alternatives for the treatment of blight could destabilise organic potato production.

Findings and conclusions regarding the use of other methods and treatments

Varieties: Planting resistant varieties would be the single most effective strategy against blight. A ban on copper would stimulate the uptake of resistant varieties, leading to drastic reduction in foliar and tuber blight. Development and widespread adoption of more varieties would take time. Uptake would also depend on market preferences.   
Alternating rows of varieties: The virulence and aggressiveness of the blight pathogen may be controlled by planting highly resistant varieties and desirable but less resistant varieties in alternating rows. Success is more likely when the pressure of blight outbreak is low. Practical problems may present for fertilisation and harvesting of different varieties.
Mixing varieties in the same row: Pathogen control may be better when up to four varieties are mixed within rows, but practical problems regarding harvesting and separation of varieties are bigger. This strategy could be effective on a smaller scale. The disease is unlikely to be suppressed more than expected for the average resistance of the mixed varieties. When planting susceptible yet highly desirable varieties mixed with less desirable yet highly resistant varieties, the success of the susceptible varieties may be improved.
 Intercropping:  Crops of a different species planted between fields or rows of potatoes should provide barriers against the spread of blight spores. Taller crops such as wheat should be better than clover, but yield may be affected by competition between species. Bigger plot size should decrease the effects of blight. Plots planted perpendicular to the wind, with grass-clover as intercrop, enjoyed greatest reduction in blight during trials.
Planting earlier: Earlier planting leads to earlier tuber bulking, which may secure yield before blight attacks. This strategy is already widely used.
Chitting/pre-sprouting seed tubers: Chitting causes tubers to bulk earlier, which may secure yield before blight attacks. The strategy requires extra labour. It is already widely used.
Defoliation: Removing infected foliage by burning with a propane gas burner kills the blight spores, but cost of gas and use of fossil energy are problematic. Flailing is less effective, but still better than doing nothing when foliage is infected with blight. No gas required when flailing.  
 Management of soil fertility: Optimal fertilization does not have direct effects on blight, but does improve yield and general vitality of plants. The availability of manure is a factor. Weather and rotation practices also affect nutrient availability to the crop. 
Rotation:  The position of the potato crop in the rotation cycle has no effect on blight, but yield is affected through nutrient supply from the preceding crop.  However, the optimal position for potatoes in the rotation cycle may not be optimal for other crops.
Volunteer removal: Pigs can be used to remove volunteer tubers which are a source of blight inoculum, but pigs are not available on all farms and may cause damage to soil structure.
Planting density: Very low planting density reduces late blight, but because of adverse effects on tuber size grading lies outside normal commercial limits and is therefore not a feasible option.

Irrigation:  To improve yield and tuber quality, drought should be avoided through irrigation, but long periods of leaf wetness should be avoided to prevent the spread of blight infection. Yield and quality can be improved on many farms, but water for irrigation purposes is not available to all.
Compost extracts: This method is not yet developed enough for practical applicability. It is not clear which compost feedstocks and methods of preparing extracts should be used, or how often and at what concentration the extracts should be used.
Foliar sprays and microbial inocula: There has been success in some crops, but there is not conclusive demonstration of effectiveness against blight under field conditions.  
Microbial antagonists and plant extracts: Spraying antagonists and plant extracts was effective up to 70% in glasshouse trials and 45% in semi-field trials, but had low effect under field conditions.
Application equipment: Underleaf spraying equipment and air assisted sprayers both gave a more uniform cover, especially for copper-based fungicides. High equipment costs  and labour requirements are the biggest limitations.
Alternative sprays: Within the range of organic regulations, no effective products were found.
Copper fungicides:  Spraying lower dosages (2kg/ha/year) of copper fungicides can be widely practiced. Significant reduction in dosages showed only slight reduction in protection against blight.

Summary

Some strategies investigated by Blight-MOP researchers are not yet applicable in practice. Other practices are applicable and will have effects on crop performance and/or blight management. Such practices are: use of resistant varieties, chitting, planting earlier, effective fertilization and irrigation regimes, crop rotation, defoliation and use of copper sprays.
Organic growers will have to identify individual strategies or combinations of strategies that are applicable to their specific circumstances and develop methods of using these strategies for optimal gain. This is most likely to lead to improved crop performance because of better blight control, and/or better growth and higher yields, and/or lower costs. The challenge for farmers and their advisors is to identify particular areas where existing blight management strategies can be refined, or where strategies not used before can be introduced.   
 
For detailed and in-depth discussions and analyses of individual strategies, refer to the Final Blight-MOP report.  The authors of the report were indebted to the farmers for their collaboration and the study was funded by the European Community (EU Fifth Framework project QLK5-CT-2000-01065:Blight-MOP – development of a systems approach for the management of late blight in EU organic potato production).