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  • From: Gene GeRue <genegerue AT ruralize.com>
  • To: "homestead AT lists.ibiblio.org" <homestead AT lists.ibiblio.org>
  • Subject: [Homestead] The Overstory #163--Mixed species cropping to manage pests and diseases
  • Date: Tue, 25 Oct 2005 08:18:18 -0500


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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
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Address: P.O. Box 428, Holualoa, Hawaii 96725 USA
Email: overstory AT agroforestry.net ; Web site:
http://www.overstory.org

Past editions of The Overstory: http://www.overstory.org

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This journal is designed to provide agricultural information, but
is sent with the understanding that the editors and publishers are
not engaged in rendering consultation. If expert assistance is
required, the services of a professional should be sought.


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  • [Homestead] The Overstory #163--Mixed species cropping to manage pests and diseases, Gene GeRue, 10/25/2005

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