October 4, 2012
On the 230,000 hectares (2009) of land dedicated to vegetable crops in France, producers are confronted by a dilemma: firstly, they are seeing a rise in damage caused by soil-borne pests, and secondly, they are obliged to comply with increasingly draconian regulations on the use of fumigants. To make up for this lack of crop protection methods, INRA researchers worked in a network with experimentation and development stakeholders.The PraBioTel project, carried out from 2009 to 2011 and led by the CTIFL (Inter-Branch Technical Centre for Fruits and Vegetables), with support from the CASDAR (Dedicated Budget for Agricultural and Rural Development) and the GIS PIClég (Scientific Interest Group for Integrated Vegetable Production), resulted in some new technical solutions for producers.
The production of vegetable crops in France (1% of UAA, 6.4% of agricultural value added), in open fields or unheated greenhouses, is based on a cropping system that can be qualified as intensive. Numerous pests present in the soil (pathogenic fungi, nematodes) may target several different crops, but the same crop may also be attacked by different pests. Since the use of methyl bromide was banned in 2005, and in light of increasing demands from society regarding environmental and product quality issues, a review of the crop protection techniques available for vegetable crops had become essential.
The scientists focused on new, soil-improving, integrated and managed cultivation practices at the scale of open-field or unheated shelter production systems. Combining these methods, and modulating their complementarity, were the research areas targeted by the partners* in the PraBioTel project. As a result of this global approach to the control of soil-borne pests, it became clear that the crop sequence and management of the intercropping period were the crucial points in these cropping systems.
Stretching from Normandy to the Mediterranean coast, a network of 13 study sites, covering a broad range of soil and climatic conditions, was set up throughout France. The research project was carried out on systems that included salad crops in the winter to account for production under shelters, and leek or carrot crops in open-field systems. This system was supplemented by surveys of producers and interviews with advisors and technicians in order to gain a clearer understanding of standard practices and to detect, if relevant, any obstacles to change or the determining factors (economic, technical or structural) that drove producers in their choice of practices.
The soil-improving practices tested involved the input of different green fertilisers, including brown mustard (Brassica juncea) for open-field crops. For sheltered crops, soil-improving practices comprised solarisation alone, or applied after the burial of the mustard crop, the input of green fertiliser alone, crop diversification during the winter or summer, or the input of fresh organic matter.
Solarisation consists in provoking a rise in soil temperature following the application of a transparent plastic mulch that captures solar energy. Soil pathogens are not resistant to exposure for a few hours to a temperature higher than 45°C, a few days at 40°C or a few weeks at 35°C. The trials thus performed were able to demonstrate the efficacy of this method on the pests responsible for the "deterioration" of aubergine or versus Meloidygne nematodes or on pathogenic fungi such as Sclerotinia, Rhizoctonia, or Mirafiori lettuce big vein virus. The effects persisted for up to 3 years after the application of solarisation.
Biodisinfection is another technique that can be used; it consists in "poisoning" pests with the volatile compounds that arise from the degradation of certain organic products. For example, brown mustard contains sinigrine, a source of isothiocyanates, which are sulphurated compounds toxic to numerous pathogens. The decomposition of buried mustard also exerts stimulant effects on antagonistic flora. Introduction of this green fertiliser during the intercropping period requires sufficient nitrate and water inputs, but it is possible, including under shelters. The biomass produced is only useful if careful sowing is ensured. Despite this, its efficacy is not equal to that of solarisation. On the other hand, a combination of these two techniques can improve soil status and the activation of soil flora.
To diminish the infective potential of soil, other areas of research were also explored, and included cropping sequences and switches between crops. These alternatives to fumigants can procure gradual solutions, but they are sustainable in a context of generating healthier soil.
*: Participants in the PraBioTel project on the control of soil-borne pests through crop management systems: use of soil-improving practices for vegetable crops: INRA research teams, APREL (Provence Association for Vegetable Research and Experimentation) regional stations, Invenio, Sileban (Investment and Development Company for Vegetable and Horticultural Crops in Lower Normandy), Grab (Organic Farming Research Group); departmental organisations under CDDM 44 (Departmental Committee for Market-Gardening Development 44), Chambers of Agriculture for the Vaucluse and Bouches-du-Rhône Départements; Centres for Technical Studies in Agriculture (CETA Eyguières and CETA Sainte-Anne); SICA Altus.
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