Agroecological crop protection in organic farming: Relevance and limits

International audiencePlant protection is one of the major issues in organic farming. Organic crop protection (OCP) strategies often rely on a limited number of methods that provide only partial control of pests and that induce lower yields and economic performances. As a result, farmers hesitate to adopt these strategies and doubts are cast on the ability of organic agriculture to feed the world. This chapter questions how agroecological concepts may contribute to OCP, while taking the different alternative schemes already developed to manage, integrate and design crop protection strategies into account. As demonstrated by a bibliographic analysis, Integrated pest management (IPM) remains the leading paradigm in crop protection. It also provides its foundational basis, giving priority to bioecological processes and alternative techniques to reduce pesticide use. Beyond IPM, agroecology is characterised by a holistic approach and the importance given to the design of a “healthy” agroecosystem. In practice, all these concepts are subject to various interpretations, and organic farming includes a variety of practices, ranging from intensive input substitution to a comprehensive integrated approach. This paper provides key elements for crop protection in OF on the basis of the adaptation of the agroecological crop protection approach. Based on a successful case study of fruit fly management in OF in Reunion Island (France), we highlight three major pillars to design pest management strategies: sanitation, habitat manipulation and conservation biological control. Finally, in the field of crop protection, this paper shows that organic farming can be both a prototype for designing innovations and a source of practices to be extended to other types of agroecosystem

Suppression of soil-borne pathogens of tomato by composts derived from agro-industrial wastes abundant in Mediterranean regions

We studied nine composts derived from wastes and by-products of the olive oil, wine, and Agaricus mushroom agro-industries. They were mixed with peat at 1:3 w w (-1) ratios and comparatively evaluated in pot experiments to assess suppressiveness against soil-borne and foliar pathogens of tomato. All compost amendments demonstrated high levels of suppressiveness against Phytophthora nicotianae Breda de Haan in tomato, when they were applied directly after curing (T0) indicating the occurrence of a "general suppression phenomenon" (81-100% decrease in plant disease incidence). They were, however, relatively less effective when applied 9 months after curing (T1, 55-100% disease decrease). Suppressiveness against Fusarium oxysporum f.sp. radicis-lycopersici Jarvis & Shoemaker was relatively lower and varied widely among composts (8-95% and 22-87% decrease in plant disease incidence for T0 and T1, respectively). Three of the composts conferred induced systemic resistance against the foliar pathogen Septoria lycopersici Speg. Biotic properties were determined, including respiration, fluorescein diacetate hydrolysis, and beta-glucosidase activity of composts. The comparative evaluation of the nine composts revealed no shared critical biotic or abiotic characteristics indicative of their suppressive effects on the soil-borne and foliar pathogens. The complex origin of compost suppressiveness is discussed and the implementation of individual evaluation of each compost product for a specific use is advocated

Soil solarization and sustainable agriculture

Pesticide treatments provide an effective control of soilborne pests in vegetable and fruit crops, but their toxicity to animals and people and residual toxicity in plants and soil, and high cost make their use hazardous and economically expensive. Moreover, actual environmental legislation is imposing severe restrictions on the use or the total withdrawal of most soil-applied pesticides. Therefore, an increasing emphasis has been placed on the use of nonchemical or pesticide-reduced control methods. Soil solarization is a nonpesticidal technique which kills a wide range of soil pathogens, nematodes, and weed seeds and seedlings through the high soil temperatures raised by placing plastic sheets on moist soil during periods of high ambient temperature. Direct thermal inactivation of target organisms was found to be the most important mechanism of solarization biocidal effect, contributed also by a heat-induced release of toxic volatile compounds and a shift of soil microflora to microorganisms antagonist of plant pathogens. Soil temperature and moisture are critical variables in solarization thermal effect, though the role of plastic film is also fundamental for the solarizing process, as it should increase soil temperature by allowing the passage of solar radiation while reducing energetic radiative and convective losses. Best solarizing properties were shown by low-density or vynilacetate- coextruded polyethylene formulations, but a wide range of plastic materials were documented as also suitable to soil solarization. Solar heating was normally reported to improve soil structure and increase soil content of soluble nutrients, particularly dissolved organic matter, inorganic nitrogen forms, and available cations, and shift composition and richness of soil microbial communities, with a marked increase of plant growth beneficial, plant pathogen antagonistic or root quick recolonizer microorganisms. As a consequence of these effects, soil solarization was largely documented to increase plant growth and crop yield and quality along more than two crop cycles. Most important fungal plant pathogenic species were found strongly suppressed by the solarizing treatment, as several studies documented an almost complete eradication of economically relevant pathogens, such as Fusarium spp., Phytophthora spp., Pythium spp., Sclerotium spp., Verticillium spp., and their related diseases in many vegetable and fruit crops and in different experimental conditions. Beneficial effects on fungal pathogens were stated to commonly last for about two growing seasons and also longer. Soil solarization demonstrated to be effective for the control of bacterial diseases caused by Agrobacterium spp., Clavibacter michiganensis and Erwinia amylovora, but failed to reduce incidence of tomato diseases caused by Pseudomonas solanacearum. Solarization was generally found less effective on phytoparasitic nematodes than on other organisms, due to their quicker soil recolonization compared to fungal pathogens and weeds, but field and greenhouse studies documented consistant reductions of root-knot severity and population densities of root-knot nematodes, Meloidogyne spp., as well as a satisfactory control of cyst-nematode species, such as Globodera rostochiensis and Heterodera carotae, and bulb nematode Ditylenchus dipsaci. Weeds were variously affected by solar heating, as annual species were generally found almost completely suppressed and perennial species more difficult to control, due to the occurrence deep propagules not exposed to lethal temperature. Residual effect of solarization on weeds was found much more pronounced than on nematodes and most fungal pathogens. Soil solarization may be perfect fit for all situations in which use of pesticides is restricted or completely banned, such as in organic production, or in farms located next to urban areas, or specialty crops with few labeled pesticides. Advantages of solarization also include economic convenience, as demonstrated by many comparative benefit/cost analyses, ease of use by growers, adaptability to many cropping systems, and a full integration with other control tools, which makes this technique perfectly compatible with principles of integrated pest management required by sustainable agriculture