Ecological Basis for Low-Toxicity Integrated Pest Management 187Farmers in Korea who face heavy disease pressure can learn to predict potential
outbreaks using educational activities that combine various weather and agro-
nomic input parameters with disease outcomes. Computer-based models are also
being commercially sold to predict disease potential based on meteorological mon-
itoring. With increasing nitrogen applications, however, greater disease incidence
can also be expected.
Weeds
The origin of puddling for lowland rice cultivation is thought to have been invented
to create an anaerobic environment that effectively kills several weeds including
weedy and red rice. In most IPM programmes for lowland rice, weed management
has therefore been closely considered part of agronomic practices during puddling
and later during aeration of the soil with cultivators. At least two hand weedings
are necessary in most crops, and considered in many countries economically viable
due to low labour cost or community obligations to the land-less, who are then
allowed to participate in the harvest. With rising labour costs, decreasing labour
availability and more effective herbicides, this situation is rapidly changing to one
of using one or two applications of pre- or post-emergence herbicides. As in the
case of fungicides, it is critical that these herbicides do not upset natural enemies,
fish or other beneficial/non-target organisms in the aquatic ecosystem including
microorganisms (see Figure 9.1). In the case of upland rice, similar changes are
rapidly occurring although better dry land cultivators are already being developed
for inter-row cultivation as an alternative to herbicides.
Non-herbicide but low labour weed management methods are also emerging
from the organic agriculture sector. The International Association of Rice Duck
Farming in Asia supports research and exchanges among mostly organic farmers.
In rice–duck farming, a special breed of duck is allowed to walk through the field
looking for food that is either broadcast or naturally occurring, and the action of
walking up and down the rows is sufficient to control most weeds. In Thailand,
mungbean and rice are broadcast together with some straw covering in rainfed rice
fields. When the rains come, both crops germinate. If there is abundant rain, the
mungbean will eventually die and become part of the mulch, but if the rain is
insufficient for the rice then the mungbean will be harvested.
No-till, no-herbicide combined with ground cover from winter barley straw or
Chinese milky-vetch is being used in South Korea in both conventional and organic
systems. Organic farmers in California use a water management system in which
there is a period of deep (30cm) flooding followed by complete drying – the rice can
take the changes but young weeds cannot. A widely adopted method in Central Thai-
land involves growing rice from ratoons. After harvest the stubble is covered with
straw and then irrigated which allows the rice plant to emerge. This method not only
controls weeds effectively but also increases organic matter and requires no tilling.
However, for the majority of rice cultivation, labour saving often means mov-
ing towards direct seeded rice and thus more weed problems. Red rice (weedy