Fish-farming in Vietnamese rice fields fights golden apple snail pest
An FAO project in Viet Nam has found that rice-fish farming - where fish are raised in the paddy-fields - is one of the best ways to control a Latin American snail that has invaded most of the rice production areas in Asia. The golden apple snail has become a serious threat to rice production over the past two decades. In field experiments under the project, the common carp has been found to reduce populations of the snail, particularly young snails with a shell height of less than 1 cm, in rice fields by up to 90 percent over a period of three months.
Studies in the early 1990s in the Philippines, ten years after the snail was introduced for snail farming, revealed that nearly all rice farmers interviewed considered the snail their greatest pest problem. Asian rice farmers have tried a variety of responses to the infestations - hand-picking snails, transplanting older rice seedlings that are no longer vulnerable to the mollusc and raising ducks in the paddy fields. Nevertheless, replanting often was the only answer. At that time it was shown in successful field trials in the Philippines that fish as snail feeders can keep snail populations in rice fields in check. Rice-fish farming serves a dual purpose. It controls the snails and enhances the food security of the rice farmers by supplementing their diets and generating income.
About 40 percent of the farmers interviewed in the Philippines were using pesticides in an attempt to control the snail. However, in addition to being costly, most of the pesticides applied were not registered for use against molluscs in freshwater ecosystems, and had serious repercussions for environmental and human health. Farmers in the Philippines applying widely used tin-based compounds with backpack sprayers, without protection, subsequently suffered from peeling toes and fingernails, headaches, skin disorders and blindness.
In Viet Nam, the government banned snail farming after an emergency meeting in July 1992, and until the massive snail population increase in 1996, had spent billions of Vietnamese Dong (millions of US$) on campaigns to build awareness about the snails and control their spread manually.
When FAO was asked to intervene, IPM was identified as the most suitable approach for snail control. Work under the FAO project in Viet Nam is ongoing in three areas:
Under the training programme so far, 52 Plant Protection Officers have been trained as trainers in integrated snail management including: the role of fish in integrated pest management, how fish can control snail populations in rice fields, and what management is necessary for the efficient use of fish for snail control. These officers have run 168 Farmers' Field Schools on integrated snail management for some 4 900 farmers.
The snail infestation in Viet Nam has been mapped and the GIS is increasingly used as an important tool to evaluate both the spread of snails and the impact of control measures (see map).
FAO expert in rice-fish farming, Matthias Halwart, said, "The results of the project so far look very encouraging. Biological control of the snail is a high priority, both as an effective long-term solution to the infestation, and as a means of reducing the excessive pesticide usage that normally results from the introduction of an exotic pest."
30 April 1998