Applying agroecological concepts to the
development of Ecologically Pest Management
strategies
Miguel
A. Altieri
Clara Ines Nicholls
1. Most of the
scientist toda would agree that conventional
modern agriculture faces an environmental
crisis. Land degradation, salinization,
pesticide pollution of soil, water and food
chains, depletion of ground water, genetic
homogeneity and associated vulnerability, all
rise serious questions regarding the
sustainability of modern agriculture.
2. The causes
of environmental crisis rooted in a prevalent
socioeconomic system which promotes
monocultures and the use of high input
technologies and agricultural practices that
lead to natural resource degradation. Such
degradation is not only an ecological
process, but also a social and
political-economic process. This is why the
problem of agricultural production cannot be
regarded only as technological one, but while
agrreing that productivity issues represent
part of the problem, attention to social,
cultural and economic issues that account for
the crisis is crucial.
3. The loss of
yields due to pests in many crops, despite
the substantial increase in the use of
pesticides is a symptom of the environmental
crisis affecting agriculture. It is well
known that cultivated plants grown in
genetically homogeneous monocultures do not
possess the necessary ecological defense
mechanisms to tolerate the of outbreaking
pest populations. Modern agriculturists heve
selected crops for high yields and high
palatability, making them more susceptible to
pests by sacrificing natural resistance for
productivity. On the other hand, modern
agricultural practices negatively affect
pests' natural enemies, which in turn do not
find the necessary environmental resources
and opportunities in monocultures to
effectively and biologically suppress pests.
Thus while the structure of the monocultures
is maintained as the structural base of
agricultural systems, pest problems will
continue to be the result of a negative
treadmill that reinforces itself. Thus the
major challenge for those advocating EBPM is
to find strategies to overcome the ecological
limits imped by monoculture.
4. IPM
approaches have not addresed the ecological
causes of the environmental problems in
modern agriculture which are deeply rooted in
the monoculture structure prevalent in large
scale production systems. There still
prevails a narrow view that specific causes
affect productivity, and overcoming the
limiting factor (i.e. insect pest) via new
technologies, continues to be the main goal.
In many IPM projects the main focus has been
to substitute less noxious inputs for the
agrochemicals that are blamed for so many of
the problems associated with conventional
agriculture. Emphasis is now placed on
purchased biological inputs such as Bacillus
thuringiensis, a microbial pesticide that is
now widely applied in place of chemical
insecticide. This type of technology pertains
to a dominant technical approach called input
substitution. The thrust is highly
technological, with the limiting factor
mentality that has driven conventional
agricultural research in the past.
Agronomists and other agricultural scientists
have for generations been taught the
"law of the minimum" as a central
dogma. According to this dogma, at any given
moment there is a single factor limiting
yield increases, and that factor can be
overcome with an appropiate external input.
Once the hurdle of the first limiting factor
has been surpassed-nitrogen deficiency, for
example, with urea as the correct input-then
yields may rise until another factor-pests,
say-becomes limiting in turn due to increase
levels of free nitrogen in the foliage. That
factor then requires another input-pesticide
in this case-and so on, perpetuating a
process of treating symtoms rather than the
real causes that evoked the ecological
unbalance.
5. Emerging
biotechnological approaches do not differ as
they are being pursued to patch up the
problems (e.g. pesticide resistance,
pollution, soil degradation, etc.) caused by
previous agrochemical technologies promoted
by the same companies now leading the
bio-revolution. Transgenic crops developed
for pest control closely follow the paradigm
of using single control mechanism (a
pesticide) that has proven to fail over and
over again with insects, pathogens and weeds
(National Research Council, 1996). Transgenic
crops are likely to increase the use of
pesticides and to accelerate the evolution of
'super weeds' and resistant insect pests
(Rissler and Mellon, 1996).
The 'one
gene-one pest' approach has proven to be
easily overcome by pests that are
continuously adapting to new situations and
evolving detoxification mechanisms (Robinson,
1996). There are many unanswered ecological
questions regarding the impact of the release
of transgenic plants and microorganisms into
the environment. Among the major
environmental risks associated with
genetically engineered plants are the
unintended transfer to plant relatives of the
'transgenes' and the unpredictable ecological
effects (Rissler and Mellon, 1996).
Given the
above considerations, agro-ecological theory
predicts that biotechnology will exacerbate
the problems of conventional agriculture. By
promoting monocultures it will also
under-mine ecological methods of farming,
such as rotations and polycultures
(Hindmarsh, 1991). As presently conceived,
biotechnology does not fit into the broad
ideals of sustainable agriculture
(Kloppenburg and Burrows, 1996).
6. This view
has diverted agriculturists from realizing
that limiting factors only represent symptoms
of a more systematic disease inherent to
unbalances within the agroecosystem and from
an appreciation of the context and complexity
of agroecological processes thus
understimating the root causes of
agricultural limitations. A useful framework
to accomplish this is to use agroecological
principles.
Agroecology
goes beyond a one-dimensional view of
agroecosystems-their genetics, agronomy,
edaphology- to embrace and understanding of
ecologiacl and social levels of coevolution,
structure, and function. For agroecologists,
sustainable yield in the agroecosystem
derives from the proper balance of crops,
soils, nutrients, sunlight, moisture, and
other coexisting organisms. The agroecosystem
is productive and healthy when these balanced
and rich growing conditions prevail and when
crop plants remain resillient to tolerate
stress and adversity. Occasional disturbances
can be oovercome by a vigorous agroecosystem
which is adaptable and diverse enough to
recover once the stress has passed.
Occasionally strong measures (i.e. botanical
insecticides, alternative fertilizers, ect. )
may need to be applied by farmers employing
alternative methods to control specific pests
or soil problems. Agroecology provides the
guidelines to carefully manage agroecosystems
without unnecessary or irreparable damage.
Simultaneous with the struggle to fight
pests, diseases, or soil deficiency, the
agroecologist strives to restore the
resiliency and strength of the agroecosystem.
If the cause of disease, pests soil
degradation, and so forth, is understoodas
imbalance, then the goal of the
agroecological treatment is to recover
balance. In agroecology, biodiversification
is the primary technique to evoke self
regulation and sustainability.
7. From a
management perspective, the agroecological
objective is to provide a balanced
environment, sustained yields, biologically
mediated soil fertility and natural pest
regulation through the design of diversified
agroecosystems and the use of low-input
technologies. The strategy is based on
ecological principles that lead management to
optimal recycling nutrients and organic
matter turnover, closed energy flows, water
and soil conservation and balanced pest-
natural enemy populations. The strategy
exploits the complementarities and synergisms
that result from the various combinations of
crops, trees and animals in spatial and
temporal arrangements. These combinations
determine the establishment of a planned and
associated functional biodiversity which
performs key ecological services in the
agroecosystem.
8. The optimal
behavior of agroecosystems depends on the
level of interactions between the various
biotic and abiotic components. By assembling
a functional biodiversity, it is possible to
initiate synergisms which subsidize
agroecosystem processes by providing
ecological services such as the activation of
soil biology, the recycling of nutrients, the
enhancement of beneficial anthropods and
antagonists, and so on.
In other
words, ecological concepts are utilized to
favor natural processes and biological
interactions that optimize synergies so that
diversified farms are able to sponsor their
own soil fertility, crop protection and
productivity. By assembling crops, animals,
trees, soils and other factors in
spatial/temporal diversified schemes, several
processes are optimized. Such processes (i.e.
organic matter accumulation, nutrient
cycling, natural control mechanisms, etc.)
are crucial in determining the sustainability
of agricultural systems.
9. Agroecology
takes greater advantage of natural processes
and beneficial on farm interactions in order
to reduce off-farm input use and to improve
the efficiency of farming systems.
Technologies emphasized tend to enhance the
functional biodiversity of agroecosystems as
well as the conservation of existing on-farm
resources. Promoted technologies are
multi-functional as their adoption usually
means favorable changes in various components
of the farming systems at the same time.
10. For
example, legume based crop rotations, one of
the simplest forms of biodiversification can
simultaneously optimize soil fertility and
pest regulation. It is well known that
rotations improve yields by the known action
of interrupting weed, disease and insect
lifecycles. However, they can also have
subtle effects such as enhancing the growth
and activity of soil biology, including
vesicular arbuscular mycorrhizae (VAM), which
allow crops to more efficiently use soil
water nutrients.
Another
practice is cover cropping or the growing of
pure or mixed stands of legumes and cereals
protect the soil against erosion; ameliorate
soil structure; enhance soil fertility, and
suppers pests including weeds, insects, and
pathogens. cover crops can improve soil
structure and water penetration, prevent soil
erosion, modify the microclimate and reduce
weed competition. Besides these effects,
cover crops can impact the dynamics of
orchards and vineyards by enhancing soil
biology and fertility and by increasing the
biological control of insect pest
populations.
11. Perhaps
the most dramatic example of the integrative
effects of a multi-purpose technology in
simultaneously enhancing IPM and soil
fertility management is organic soil
fertilization.
Some studies
suggest that the physiological susceptibility
of crops to insects may be affected by the
form of fertilizer used (organic vs. chemical
fertilizer). Studies documenting lower
density of several insect herbivores in
low-input systems, have partly attributed
such reduction to a low nitrogen content in
the organically farmed crops.
12. The
ultimate goal of agroecological design is to
integrate components so that overall
biological efficiency is improved,
biodiversity is preserved, and the
agroecosystem productivity and its
self-sustaining capacity is maintained. The
goal is to design an agroecosystem that
mimics the structure and function of natural
ecosystem, that is systems that include:
(a)
Vegetative cover as an effective soil-and
water-conserving measure, met through the
use of no-till practices, mulch farming,
and use of cover crops and other
appropiate methods.
(b) A regular supply of organic matter
through the regular addition of organic
matter (manure, compost and promotion of
soil biotic activity).
(c) Nutrient recycling mechanisms through
the use of crop rotations, crop/livestock
systems based on legumes, etc.
(d) Pest regulation assured through
enhanced activity of biological control
agents achieved by introducing and/or
conserving natural enemies.
13. The
process of converting a conventional crop
production system that relies heavily on
systemic, petroleum-based inputs to a
diversified agroecosystem with low-inputs is
not merely a process of withdrawing external
inputs without compensatory replacement or
alternative management. Considerable
ecological Knowledge is required to direct
the array of natural flows necessary to
sustain yields in a low-input system.
The process of
conversion from a high-input conventional
management to a low-externalinput management
is a transitional process with four marked
phases:
(a)
Progressive chemical withdrawal.
(b) Rationalization and efficiency of
agrochemical use through integrated pest
management (IPM) and integrated nutrient
management.
(c) Input substitution, using
alternative, low-energy input
technologies.
(d) Redising of diversified farming
systems with an optimal crop/animal
integration which encourages synergisms
so that the system can sponsor its own
soil fertility, natural pest regulation,
and crop productivity.
During the
four phases, management is guided in order to
ensure the following processes:
(a)
Increasing biodiversity both in the soil
and above ground
(b) Increasing biomass production and
soil organic matter content
(c) Decreasing levels of pesticide
residues and losses of nutrients and
water components
(d) Establishment of functional
relationships between the various plant
and animal farm components
(e) Optimal planning of crop sequences
and combinations and efficient use of
locally available resources.
14. The
challenge for EBPM scientists is to identify
the correct management techniques and crop
assemblages that will provide through their
biological synergisms key ecological services
suchh as nutrient cycling, biological pest
control, and water and soil conservation.
The
exploitation of these synergisms in real
situations involves agroecosystem design and
management and requires an understanding of
the numerous relationships among soils,
plants, herbivores, and natural enemies.
Clearly, the emphsis of this approach is to
help to restore natural control mechanisms
through the addition of selective
biodiversity within and outside the crop
field, through a whole array of possible crop
arragement in time and space.
