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Economic growth threatens to bring herbicide overuse to Asia
STANFORD -- Asia's economic growth is dramatically changing the region's agriculture as people rise out of poverty, said experts who attended an international conference on rice farming March 28-30 at Stanford University.
Asian farmers are finding it increasingly difficult to hire workers to transplant and weed rice by hand as their national economies create better-paying industrial jobs, conference participants said. The result is that farmers in some regions are rapidly switching to a less labor- intensive form of rice farming that greatly increases their dependence on herbicides.
Meanwhile, international research efforts are under way to produce rice varieties that can stay ahead of the growing demand for rice, and those varieties are direct-seeded, rather than transplanted, varieties, which will further encourage farmers to use herbicides.
But herbicides, if used without enough understanding of the mostly tropical eco-systems into which they are being introduced, could lead to future reductions in rice yields as well as cause damage to human health and the environment, said those attending the conference - an international group of economists, plant breeders, agronomists, ecologists, epidemiologists and managers from public research institutions, private agri-chemical companies and academia.
"It's very clear now that if you use a single herbicide over time, you build up resistance in weeds to that herbicide, and you can actually have a yield loss," instead of a gain, said Stanford University economist Rosamond Naylor, who organized the conference, which was sponsored by the Rockefeller Foundation.
"We could go down the same chemical path with herbicides that we went down earlier with insecticides," said Naylor, a research fellow with Stanford's Institute for International Studies. The institute's researchers focus on land use change and biotechnology transfer to developing countries, as well as market-based incentives for pollution abatement and environmental regulation. Naylor co-chaired the conference with Walter Falcon, director of the Stanford institute and Donald Kennedy, Stanford president emeritus, who directs the institute's environmental policy program.
Overuse of antibiotics
A similar path also was taken with overuse of antibiotics and has led to increasing disease resistance to them, said Stanford biologist Paul Ehrlich. "The huge price advantage farmers see at first from using herbicides will go down," he predicted, as more and more weeds develop resistance.
Approximately 4.9 tons of rice per hectare are produced in Asia on 70 million hectares of irrigated land. To keep up with projected demand, the yield per hectare must increase to 8 tons per hectare in the next 30 years, conference participants said.
"The trick is to find a few easy principles that farmers can follow," said Ken Fischer, director of research for the International Rice Research Institute in Manila, Philippines. "The simple rule in the case of insecticides is 'don't spray in the next 40 days' " after planting, he said. The rule comes from research that indicated there is a high chance of killing insect predators with early spraying.
Herbicide use has spread rapidly with direct seeding of rice, Naylor said. "Grass weeds germinate at the same time as direct-seeded rice and look very much like the rice, which makes hand weeding nearly impossible. Herbicides that are selected specifically for weeds and that are not harmful to rice are therefore essential to grow direct-seeded varieties," said Naylor, who has studied rice production and labor practices in Indonesia and the Philippines.
"The combination of direct-seeded rice and herbicides enables farmers to reduce their labor inputs by as much as 50 percent."
Much of the production gain in rice in Asia during the past 25 years has come from continuous cropping and less crop rotation, she said, which means less opportunity to break pest cycles, and there is also no wintertime fallow to break cycles as in more temperate climates. In integrated insecticide management programs, farmers are taught to use crop rotation and biological predators as substitutes for insecticides. Similar strategies are now needed for weed control, Naylor said.
Conference participants generally agreed that herbicides are less toxic than insecticides, but many also noted that they have been found to infiltrate groundwater and cause fish kills in the United States besides creating health problems for some people who come into intense contact with them. There is virtually no monitoring of health and environmental damage from pesticides in most Asian countries, participants said.
Capital markets, training programs and environmental taxes or regulations could be designed to encourage judicious use of herbicides, said Stanford economist Larry Goulder, but that first requires more research to better understand the ecology of weeds and the on-farm and off-farm costs of herbicide use.
The conference produced a consensus for the need to undertake three types of research:
The conference participants also recommended the following policy changes be considered by international agencies and the national governments affected:
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