Rodent management in lowland rice production systems Red River delta, Vietnam

Background

Rodents cause significant damage to lowland irrigated rice crops in the Red River delta of Vietnam. A four-year study was conducted in 1999-2002 to examine the effectiveness of applying rodent control practices using the principles of ecologically based rodent management. Four study sites at a village level were selected. Farmers on two treated sites were asked to follow a set of rodent management practices, while farmers on the untreated sites were asked not to change their current practices.

The Recommendations

Farmers on the treated sites were encouraged to:

use trap-barrier systems (TBS; 25 x 25 m early planted crop surrounded by a plastic fence with multiple capture traps; one TBS for every 10-15 ha),
to work together over large areas by destroying burrows in refuge habitats soon after planting (before the rats re-establish in the fields before the onset of breeding),
synchronising planting and harvesting of rice crops,
cleaning up weeds and piles of straw, and
keeping small banks surrounding rice fields small (<30 cm) to prevent burrowing by rats.

A trap barrier system in the field

Digging out rat burrows in irrigation channel bank

The Results

There was a 75% reduction in the use of rodenticides and plastic barrier fences (without traps or an early crop) on treated sites. However, the abundance of rodents was low after the implementation of the treatments across all sites. There was no evidence for a treatment effect on the abundance of rats captured each month using live-capture traps between treated and untreated sites, no difference in damage and no difference in rice yields. While the low rat abundance was unfortunate for the project, the results demonstrate that ecologically based rodent management was equally effective as current practices in managing rodent pests, and led to significantly better environmental benefits by reducing reliance on poisons and excess use of plastic fencing. Also, farmers on the treated sites spent considerably less money applying rodent control practices, which was reflected in the comparative increase in the partial benefit:cost of applying ecologically based rodent management. Prior to the implementation of treatments the ratio was 3:1. In the final year of the project the benefit:cost ratio was as high as 17:1 on treated sites.

The project also achieved some other positive results. Data on rodents from Vietnam were added to that from other countries to compile the first rodent taxonomic key developed for all the significant rodent pest species and common non-pest rodent species in SE Asia. The key plus species distribution maps, photos of key physical features and a brief description of the biology of each species are part of an ACIAR Monograph (No. 100) “Field methods for rodent studies in Asia and the Indo-Pacific” (K P Aplin, P R Brown, J Jacob, C J Krebs & G R Singleton, 2003). The project also facilitated the placement of an Australian Youth Ambassador Abroad position in Vietnam. Ms Susie Williams worked for 5 months with colleagues at the National Institute for Plant Protection in Hanoi, and 1 Master of Science and 2 Bachelor of Science students undertook studies as part of this project.

Placing a radio-collar on a Rice-field Rat (Rattus argentiventer)

Rat damage to a kohlrabi plant

Strong emphasis on community involvement has led to rapid transfer of this technology. Key elements of these management strategies are now on trial in eight provinces in the Mekong delta and 10 provinces in the Red River delta.

A rice crop during tillering stage

An AusAID capacity-building project on rodent management in the Mekong delta was based on outputs from this and a previous project. This AusAID project led to Plant Protection Department extension staff from 17 provinces being trained in community-based rodent management. There was good adoption of these management practices in the province where the project was based, with spill-over adoption in neighbouring provinces.

An ACIAR/World Vision project led to high levels of adoption of community-based management of rodents in Binh Thuan province in the Mekong delta, with spill-over adoption in another province in the north of Vietnam.

A ripening rice crop

A ripening sticky-rice crop

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