Agron. Sustain. Dev. (2012) 32:273–303 DOI 10.1007/s13593-011-0022-4 REVIEW ARTICLE Plant species diversity for sustainable management of crop pests and diseases in agroecosystems: a review Alain Ratnadass & Paula Fernandes & Jacques Avelino & Robert Habib Accepted: 11 December 2010 /Published online: 17 May 2011 # The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Farmers are facing serious plant protection issues disruption of the spatial cycle, (3) disruption of the temporal and phytosanitary risks, in particular in the tropics. Such cycle, (4) allelopathy effects, (5) general and specific soil issues are food insecurity, lower income in traditional low- suppressiveness, (6) crop physiological resistance, (7) con- input agroecosystems, adverse effects of pesticide use on servation of natural enemies and facilitation of their action human health and on the environment in intensive systems against aerial pests and (8) direct and indirect architectural/ and export restrictions due to strict regulations on quarantine physical effects. Here we review the reported examples of pests and limits on pesticide residues. To provide more and such effects on a broad range of pathogens and pests, e.g. better food to populations in both the southern and northern insects, mites, myriapods, nematodes, parasitic weeds, fungi, hemispheres in a sustainable manner, there is a need for a bacteria and viruses across different cropping systems. Our drastic reduction in pesticide use while keeping crop pest and review confirms that it is not necessarily true that vegetational disease damage under control. This can be achieved by diversification reduces the incidence of pests and diseases. breaking with industrial agriculture and using an agro- The ability of some pests and pathogens to use a wide range of ecological approach, whose main pillar is the conserva- plants as alternative hosts/reservoirs is the main limitation to tion or introduction of plant diversity in agroecosystems. the suppressive role of this strategy, but all other pathways Earlier literature suggest that increasing vegetational identified for the control of pests and disease based on plant biodiversity in agroecosystems can reduce the impact of species diversity (PSD) also have certain limitations. Improv- pests and diseases by the following mechanisms: (1) ing our understanding of the mechanisms involved should resource dilution and stimulo-deterrent diversion, (2) enable us to explain how, where and when exceptions to the : above principle are likely to occur, with a view to developing A. Ratnadass (*) P. Fernandes sustainable agroecosystems based on enhanced ecological CIRAD, UPR HortSys, processes of pest and disease control by optimized vegeta- F-34398 Montpellier, France e-mail: [email protected] tional diversification. J. Avelino Keywords Integrated pest management . Agroecology. CIRAD, UPR Bioagresseurs: Analyse et maîtrise du risque, Conservation agriculture . Horticulture . Agroforestry F-34398 Montpellier, France R. Habib Contents CIRAD, Département Persyst, F-34398 Montpellier, France 1. Introduction.............................2 2. Bottom-up temporal cycle disruption of pests and P. Fernandes pathogens via non-host effects.................3 PRAM, BP 214, F-97285 Le Lamentin Cedex 2, Martinique 2.1. Hosts and non-host effects on pests and diseases..3 2.2. Examples of positive effects of introducing PSD..3 J. Avelino CATIE 7170, 2.3. Examples of alternate host-associated negative Turrialba 30501, Costa Rica effects of PSD.........................4 274 A. Ratnadass et al. 3. Bottom-up resource concentration/dilution and spatial 10.3. Instances where PSD negatively affects natural disruption of pest dynamics/pathogen epidemics....5 enemy populations and/or pest predation via provision of alternate food...............16 3.1. Evidence of resource concentration/dilution 11. Refugia/shelters for predators due to vegetative effects..............................5 structural/architectural characteristics...........17 3.2. Evidence of spatial cycle disruption effects.....6 12. Positive and negative effects of PSD on pest and 3.3. Drawbacks of species mixtures aiming at disrup- disease impact via microclimate alteration.......17 tive effects on crop pests/diseases............ 6 13. Physical barrier effects on crop pests and diseases..19 4. Pest deterrence or repellence...................6 13.1. Barrier effects against pests and pathogens at the “ ” 4.1. Evidence of positive deterrent diversion field level.............................19 effects..................................6 13.2. Barrier effects against pests and pathogens at the 4.2. Lack of evidence of positive “deterrent diversion” landscape level ........................19 effects..................................7 13.3. Negative impacts of barrier effects via natural enemy 5. Pest stimulation or attraction....................7 arrestment or facilitation of pest action........20 5.1. General principles and evidence of effectiveness of 14. Conclusions and directions for future research on the trap cropping (or “stimulant diversion”) PSD-induced effects on pests and diseases.......20 strategy..............................7 14.1. Main lessons drawn from the literature review...20 5.2. Limitations to the trap cropping strategy.......7 14.2. PSD effects at the soil and field levels .......20 6. The “Push-Pull” strategy......................8 14.3. PSD effects at the field and landscape levels...23 6.1. Principles and instances of successful implemen- 14.4. Directions for future research..............23 tation..............................8 15. Acknowledgements.........................24 6.2. Limitations to the ‘push-pull’ principles.......9 16. References .............................24 7. Below-ground bottom-up allelopathic effects.......9 7.1. Trap crops/Suicidal germination inducers ......9 1 Introduction 7.2. Direct antibiotic effects during plant growth....10 7.3. Antibiotic effect after biomass decomposition...11 Farmers, particularly in the tropics, are faced with dramatic 7.4. Limitations to the use of plants with allelopathic plant protection issues/phytosanitary risks resulting in: effects..............................12 8. Stimulation of soil pest-pathogen antagonists......12 & Food insecurity and reduced income in traditional low- input agrosystems, e.g. in subsistence systems in Sub- 8.1. Activation of general microflora and Saharan Africa macrofauna.............................12 & Adverse effects of pesticide use on human health and on 8.2. Activation of specific pathogen-antagonist micro- the environment in and around intensive systems, e.g. in organisms..............................13 French overseas islands in the Caribbean, the Indian 8.3. Instances of negative impacts of PSD via the soil Ocean or the Pacific or in peri-urban horticulture in Africa pathogen antagonist pathway...............13 & Export restrictions due to strict regulations imposed by 9. Crop physiological resistance via improved importing countries concerning quarantine pests and nutrition................................14 minimum limits on pesticide residues 9.1. “Tolerance/compensation”-like resistance......14 9.2. Non-preference (antixenosis)-like resistance....14 To provide more and better food to populations in both 9.3. Antibiosis-like resistance..................15 the southern and northern hemispheres in a sustainable 9.4. Negative impacts of PSD resulting in increased manner, there is a need for a shift from agrochemistry to disease incidence via the plant nutrition agroecology. Agroecology is based on the optimization of pathway..............................15 biological interactions and regulations in agroecosystems, 10. Top-down effects on crop pests via provision of and its application to crop protection can be referred to as alternative food.........................15 agroecological crop protection (Deguine et al. 2008). The high vulnerability of modern intensive agroecosystems 10.1. Pollen and nectar food sources for pest para- to crop damage by pests and diseases is classically ascribed to sitoids and predators....................15 over-simplification of the systems (Tilman et al. 2002). The 10.2. Shelters for alternate hosts and prey of pest hypothesis that the resilience of these intensive agroecosys- parasitoids and predators.................16 tems can be increased simply by making their traits match Plant diversity for pest and disease management 275 those of natural ecosystems or of certain low-input, diversi- Integrating selected PSD plants in agroecosystems can fied, traditional agroecosystems was therefore proposed reduce the impact of pests and diseases via several causal (Lewis et al. 1997;DawsonandFry1998;Jackson2002). pathways either individually or in combination, namely: (1) Agroecosystem diversification at different scales is one pest-suppressing effects via visual and olfactory cues: of the two pillars of the agroecological approach, alongside resource dilution and stimulo-deterrent diversionary effects; soil quality enhancement (Nicholls and Altieri 2004; Ferron (2) disruption of the spatial cycle via non-host effects; (3) a and Deguine 2005; Deguine et al. 2008). In addition to reduction in the inoculum/carry-over population thanks to agronomic benefits (Malézieux et al. 2009), introducing the absence of a host plant: disruption of the temporal vegetational diversity in agrosystems may lead to different cycle; (4) below-ground bottom-up allelopathic effects;