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[Gene GeRue <genegerue AT ruralize.com>]

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> Date: Mon, 24 Oct 2005 22:23:39 -1000
> From: "The Overstory" <overstory AT agroforestry.net>
> To: "Gene GeRue" <genegerue AT ruralize.com>
> Subject: The Overstory #163--Mixed species cropping to manage pests
>         and diseases
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> The Overstory #163--The use of mixed species cropping to manage
>      pests and diseases ­ theory and practice
> By Birgitta Rämert, Margi Lennartsson, and Gareth Davies
>
>
> Publication date: October 24, 2005
>
>
> ::::::::::::::
>
>
> The Overstory Book, 2nd Edition, a formatted, indexed and illustrated
> compilation of The Overstory ejournal editions 1 - 138 is in stock.
> Your purchase helps support publication of The Overstory:
> http://www.agroforestry.net/overstory/ovbook.html
>
>
> ADDRESS CHANGES: Please send any changes in your e-mail address to
> overstory AT agroforestry.net
>
>
> ::::::::::::::
>
> The Overstory #163--The use of mixed species cropping to manage
>      pests and diseases ­ theory and practice
> By Birgitta Rämert, Margi Lennartsson, and Gareth Davies
>
>
> Contents:
>
> : INTRODUCTION
> : MIXED SPECIES CROPPING SYSTEMS
> : MIXED SPECIES CROPPING AND PEST ATTACK
> : MIXED SPECIES CROPPING AND DISEASE ATTACK
> : CONCLUSIONS
> : REFERENCES
> : ORIGINAL SOURCE
> : ABOUT THE AUTHORS
> : RELATED EDITIONS OF THE OVERSTORY
> : PUBLISHER NOTES
> : SUBSCRIPTIONS
>
>
> ::::::::
>
>
> INTRODUCTION
>
> Mixed species cropping is the growing of two or more plant species in
> the same field in the same year and, at least in part, at the same time.
> Mixed species cropping permits an intensification of the farm system,
> which results in increased overall productivity and biodiversity in
> cropped fields (Vandermeer, 1989). Mixed species cropping has been seen
> as a promising technique to develop sustainable farming systems because
> it often has multifunctional roles and can potentially provide a number
> of eco-services within the farm system. Examples may include the
> addition and recycling of organic material, water management, protection
> of soil from erosion and pest or disease suppression. This functional
> diversity contributes to ecological processes to promote the
> sustainability of the whole farm system (Altieri, 1999).
>
>
> MIXED SPECIES CROPPING SYSTEMS
>
> Mixed intercropping systems where two, or often more species, are grown
> intermingled without distinct rows are very commonly used in the tropics
> but are not generally used in temperate organic horticulture. Although
> productivity can be high they usually require more or less intensive
> husbandry regimes. Row intercropping, growing two or more crops together
> in rows, and strip cropping, cropping growing two or more species in
> strips sufficiently wide to allow separate management regimes but
> sufficiently close to influence each other, have been more widely
> investigated in the EU and USA in recent years as they have greater
> potential for mechanisation. These latter two types of mixed species
> cropping have also been used to manipulate the system to deliver other
> eco-services such as nitrogen (N) supply where for instance a legume is
> used as an intercrop to fixate N that is used by subsequent food crops.
> They have also been extensively studied as a pest management tool and,
> to a lesser extent, as a disease management option. Other benefits can
> also include improved soil structure, improved weed control,
> microclimate manipulation (e.g. growing a tall crop to provide a wind
> barrier), providing habitat for natural enemies and even as a trap crop.
> In contrast to mixed species cropping regimes, monoculture is the
> cropping of a single species in a field. In general, as the cropping
> system moves from a random mix of plants to a monoculture the
> biodiversity of the system decreases. Total productivity also tends to
> decrease. Organic growers in the UK and northern Europe have not
> generally adopted mixed species cropping systems. This is because
> increased intensity of production often implies increased use of manual
> labour a significant immediate cost for organic growers. At present it
> is difficult to directly offset this cost against the benefits provided
> because they have not been quantified, except in a few limited cases. In
> this paper, although we present the potential role of mixed species
> cropping in pest and disease management, we argue that it will only be
> when it's full potential as a provider of a range of eco-services have
> been fully quantified and recognised that it will be widely adopted by
> growers in organic production systems.
>
>
> MIXED SPECIES CROPPING AND PEST ATTACK
>
> Studies on the effect of intercropping on pest attacks are numerous and
> often contradictory due to the difficulty of teasing out the ecological
> factors that can affect insect-plant relations. Andow (1991) analysed
> 209 studies involving 287 pest species. Compared with monocultures, the
> population of pest insects was lower in 52% of the studies (149 species)
> and higher in 15% (44 species). Of the 149 pest species with lower
> populations in intercrops 60% where [sic] monophagous and 28% polyphagous. The
> population of natural enemies of the pests was higher in the intercrop
> in 53% of the studies and lower in 9%. The results of such studies
> therefore imply a complex situation in which the specific
> agro-ecological situation is important. However, in order to develop
> mixed species cropping as a tool it is necessary to understand the
> underlying mechanisms involved. Root (1973) defined two hypotheses; (1)
> the resource concentration hypothesis and (2) the natural enemies
> hypothesis. In the former insects are attracted to and concentrated on
> their food plant resources which are more easily found or more apparent
> in simple (monoculture) systems whilst in the latter natural enemies are
> more effective and numerous in diverse systems. It seems that the first
> hypothesis more closely explains observed pest attack although the exact
> mechanism of concentration on the resource is not defined by Root
> (1973). There are currently several competing explanations which are
> probably best synthesised by Finch and Collier (2000). Their appropriate
> / inappropriate landings hypothesis posits that insect pests settle on
> plants only when various host plant factors such as visual stimuli,
> taste and smell are satisfied. This is more likely in monocultures than
> polycultures where the chance of encountering a 'wrong' stimulus is much
> increased. The complexity of the overall picture makes it difficult to
> specifically design intercrops for pest control without practical
> knowledge of pest and crop biology. Examples of intercropping that
> effectively prevents pests are the use of clover undersowing to deter
> cabbage root fly (Finch and Edmonds, 1994) and Medicago litoralis to
> deter carrot root fly (Ramert, 1993; Rämert & Ekbom, 1996). The use of
> trap crops, usually in strip cropping systems, shows variation in
> effectiveness (Hokkanen, 1991). A simulation model (Banks & Ekbom, 1999)
> indicates that the effectiveness of trap crop is correlated with the
> relative strengths of the attractiveness of the trap crop to principal
> crop. Several green manure crops were shown to be good trap crops for
> Lygus spp. in a lettuce agroecosystem (Rämert et. al 2001).
>
>
> MIXED SPECIES CROPPING AND DISEASE ATTACK
>
> Mixed species cropping has been shown to be an effective disease
> management tool, especially in cereals. For example, Vilich-Meller
> (1992), showed that mixtures of winter-rye/winter-wheat and
> spring-barley/oats reduced fungal leaf diseases and Lennartsson (1988)
> showed that a mixture of wheat and Medicago lupulina reduced the
> incidence of take-all disease of wheat, a soilborne pathogen. The
> underlying epidemiology has also been extensively modelled (Garrett &
> Mundt, 1999) from the perspective of varietal mixtures and can simply be
> explained as the reduced chance of fungal spores encountering a
> susceptible plant in a mix. The effect tends to improve with increase in
> the number of genotypes in the mix and the randomness of the mix.
> Although the epidemiology of airborne epidemics makes them amenable to
> manipulation by mixed cropping it could also be expected to alter
> microclimates within the crop and from this point of view could effect
> disease development positively or negatively.
>
>
> CONCLUSIONS
>
> Mixed species cropping is often perceived as a viable tool to increase
> on-farm biodiversity in organic agriculture and is a potentially
> important component of any sustainable cropping system. Apart from
> increasing total farm productivity, mixed species cropping can bring
> many important benefits such as improvement of soil fertility management
> and suppression of pests and/or diseases. In this sense it can be seen
> as performing different eco-services in the farm system. Mixed species
> cropping, particularly row intercropping and strip intercropping, could
> be an important tool for pest and disease management in organic farming
> systems. However, it is only likely to be widely adopted by organic
> growers once the potential benefits ­eco-services- have been fully
> evaluated and can be shown to outweigh the increased management and
> labour input that will to be necessary for the more complex cropping
> system.
>
>
> ::::::::::::::
> REFERENCES
>
> Altieri MA (1999) The ecological role of biodiversity in agroecosystems.
> Agriculture Ecosystems and Environment 74, 19-31.
>
> Andow DA (1991) Vegetational diversity and arthropod population
> response. Annual Review of Entomology 36, 561-568.
>
> Banks JE; Ekbom B (1999) Modelling herbivore movement and
> colonization:pest management potential of intercropping and trap
> cropping. Agriculture and Forest Entomology 1, 165-170.
>
> Finch S; Collier R (2000) Host-plant selection by insects ­ a theory
> based on 'appropriate/inappropriate' landings by pest insects of
> cruciferous plants. Entomologia Experimentalis et Applicata 96, 91-102.
>
> Finch S; Edmonds GH (1994) Undersowing cabbage crops with clover ­
> effects on pest insects, ground beetles and crop yield. IOBC/WPRS
> Bulletin 17(8),159-167
>
> Hokkanen H (1991) Trap cropping in pest management. Annual Review of
> Entomology 36, 119-138.
>
> Ramert B (1993) Mulching with grass and bark and intercropping with
> Medicago litoralis against carrot fly (Psila rosae (F.). Biological
> Agriculture and Horticulture 9, 125-135.
>
> Rämert B; Ekbom B (1996) Intercropping as a management strategy against
> carrot rust fly (Diptera: Psilidae): A test of enemies and resource
> concetration hypotheses. Environmental Entomology 25, 1092-1100.
>
> Rämert B;Hellqvist S; Ekbom B; Banks JE (2001) Assessment of trap crops
> for Lygus spp. in letttuce. International Journal of Pest management 47,
> 273-276.
>
> Root RB (1973) Organization of plant-arthropod association in simple and
> diverse habitats: the fauna of collards (Brassica oleracea). Ecological
> Monographs 43(1), 95-124.
>
> Garrett KA; Mundt CC (1999) Epidemiology in mixed host populations.
> Phytopathology 89(11), 984- 990.
>
> Lennartsson M (1988) Take-all disease of wheat. In: Proceedings 6th
> International IFOAM Scientific Conference, (eds Allen P & Van Dusen D),
> 575-580.
>
> Vandermeer J (1989) The Ecology of Intercropping. Cambridge University
> Press, Cambridge.
>
> Vilich-Meller V (1992) Mixed cropping of cereals to suppress plant
> diseases and omit pesticide applications. Biological Agriculture and
> Horticulture 8, 299-308.
>
>
> ::::::::::::::
> ORIGINAL SOURCE
>
> This article was reprinted with the kind permission of the authors from:
>
> Rämert, B., M. Lennartsson, and G. Davies. 2002. The use of mixed
> species cropping to manage pests and diseases ­ theory and practice. In:
> Powell et al. (eds), UK Organic Research 2002: Proceedings of the COR
> Conference, 26-28th March 2002, Aberystwyth, pp. 207-210.
>
>
> ::::::::::::::
> ABOUT THE AUTHORS
>
> Birgitta Rämert is Associate Professor in plant protrection at the
> Swedish University of Agricultural Sciences (SLU) in Uppsala, Sweden.
> She has more than 25 years of experience in conventional and ecological
> agricultural systems, especially concerning relationships between
> agricultural systems and pests and pathogen problems. During the past
> few years, her work has focused on conservation of biological controls.
> Birgitta has considerable experience with extension services for
> conventional and ecological growers. Birgitta Rämert, Department of
> Ecology and Crop Production Sciences,Swedish University of Agricultural
> Sciences, Box 7043, SE 750 07 Uppsala, Sweden.
>
> Margi Lennartsson and Gareth Davies are with IOR-HDRA, Ryton Organic
> Gardens, Coventry, CV8 3LG, UK
>
>
> ::::::::::::::
> WEB LINKS
>
> Garden Organic, information on organic gardening:
> <http://www.gardenorganic.org.uk/>
>
> Miguel Altieri's agroecology page with articles and links:
> <http://www.cnr.berkeley.edu/~agroeco3/>
>
> The Center for Agroecology & Sustainable Food Systems at the University of
> California, Santa Cruz: <http://zzyx.ucsc.edu/casfs/>
>
> The Agroecology Home links page is a rich source of site links:
> <http://www.agroecology.org/links.htm>
>
> Biodiversity Support Programme: <http://www.BSPonline.org/>
>
>
> ::::::::::::::
> RELATED EDITIONS OF THE OVERSTORY
>
> The Overstory #158--Forest Culture
> The Overstory #147--Major Themes of Tropical Homegardens
> The Overstory #109 -  Cultural Landscapes
> The Overstory #105 -  Complex Agroforests
> The Overstory #93 -  Trees, Forests and Sacred Groves
> <http://www.agroforestry.net/overstory/overstory93.html>
> The Overstory #82 - Introduction to Indigenous Knowledge
> <http://www.agroforestry.net/overstory/overstory82.html>
> The Overstory #81 - The Soil Foodweb: It's Role in Ecosystem Health
> <http://www.agroforestry.net/overstory/overstory81.html>
> The Overstory #44--Integrated Systems Approach
> <http://www.agroforestry.net/overstory/overstory44.html>
> The Overstory #21--Agroforestry and Biological Diversity
> <http://www.agroforestry.net/overstory/overstory21.html>
>
>
> ::::::::::::::
> PUBLISHER NOTES
>
>
> The Overstory Book, 2nd Edition, a formatted, indexed and illustrated
> compilation of The Overstory ejournal editions 1 - 138 is in stock.
> Your purchase helps support publication of The Overstory:
> http://www.agroforestry.net/overstory/ovbook.html
>
>
> ADDRESS CHANGES: Please send any changes in your e-mail address to
> overstory AT agroforestry.net
>
>
> ::::::::::::::
>
>
>
> Publisher: Permanent Agriculture Resources
> Editor: Craig R. Elevitch
>
> Distributor:
> The Overstory is distributed by Agroforestry Net, Inc., a nonprofit
> 501(c)(3) organization based in Hawaii.
> Address: P.O. Box 428, Holualoa, Hawaii 96725 USA
> Email: overstory AT agroforestry.net ; Web site:
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>
> Past editions of The Overstory: http://www.overstory.org
>
> This publication is Copyright 2005 Permanent Agriculture Resources.
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>
>
> ::::::::::::::
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