Ecological Basis for Low-Toxicity Integrated Pest Management 181management of inputs are rice stemborers and the various diseases discussed
below.
A major issue when considering IPM decision making is one of paths to rice
production intensification. In most cases, intensification means the use of improved
high yielding varieties, irrigation, fertilizers and pesticides – as was common in the
Green Revolution. However, two approaches to intensification should be consid-
ered. The first is input intensification in which it is important to balance an opti-
mal production level against maximizing profits and for which higher inputs can
destabilize the production ecosystem. The second route to intensification is one of
optimizing all outputs from the rice ecosystem to maximize profits. In many low-
land flooded conditions, this may mean systems such as rice–fish or rice–duck that
may be more profitable and less risky, yet require lower inputs (and often resulting
in lower rice yields). In areas where inputs are expensive, where the ecosystem is
too unstable (because of drought, flood) to ensure recovery of input investments,
or where rice is not marketed, then such a path to intensification may be more
beneficial over time. However, such a system has a different ecology due to the
presence of fish or duck, and therefore will involve a different type of IPM decision
making.
Ecological Basis of Rice IPM
IPM in much of Asian rice is now firmly based on an ecological understanding of
the crop and its interaction with soil nutrients and crop varieties. We present below
an ecological overview of our current understanding of how the rice ecosystem
operates during the development of the crop.
The rice ecosystem in Asia is indigenous to the region and its origins of domes-
tication date back 8000 years to the Yangtze Valley in southern China (Smith,
1995), and more widely some 6000 years ago (Ponting, 1991). Cultivation prac-
tices similar to those of today were reached by the 16th century (Hill, 1977). This
period of time means that rice plants, pests and natural enemies existed and
co evolved together for thousands of generations. Rice ecosystems typically include
both a terrestrial and an aquatic environment during the season with regular flood-
ing from irrigation or rainfall. These two dimensions of the rice crop may account
for the extremely high biodiversity found in the rice ecosystem and its stability
even under intensive continuous cropping – and contrasts with the relative insta-
bility of rice production under dryland conditions (Cohen et al, 1994). The irri-
gated rice systems in Africa, the Americas and Europe also include this aquatic and
terrestrial element within which high levels of biodiversity are also found.