Management of rodent pests in rice based farming systems

• Department of Agriculture and Extension, Laos
• Universiti Putra Malaysia, Malaysia
• National Institute of Plant Protection, Vietnam
• Central Research Institute for Food Crops, Indonesia

In many Southeast Asian countries and in parts of Australia, rodents can reduce food production by eating crops before the harvest. Indonesia has one of the worst reported rodent problems, with about 17% of its pre-harvest rice crop regularly ruined. Rats are the single most important pre-harvest pest there, and their economic impact is a major concern. In Vietnam rodents are also a serious problem in the agricultural sector; in Laos they are that country's second worst agricultural pest, and the one over which farmers feel they have least control.
Two previous ACIAR projects on rodents in Southeast Asia established a good understanding of the population ecology and habitat use of these pests. The scientists recognized that it was now possible to put that knowledge to use to develop affordable forms of integrated pest management (IPM) for rodents. To do so, it was necessary to integrate the outputs from the previous ACIAR projects into a cohesive management plan. This project was designed to do that.

The main aim was to extend the knowledge of more appropriate ways to manage rodent pests in various rice-growing systems, gained in earlier research activities, to village communities in Indonesia, Vietnam and Laos.

The scientists evaluated possible IPM strategies, worked closely with village farmers during testing and development of demonstration management projects to ensure that any strategies were workable at village level, and devised a training, education and extension program to put the scientific outcomes in place.
The project methodology was designed around five main objectives:
physical control with trap-barrier systems (TBS)
rodent management at village level
forecasting of rodent abundance
biological control
rodent pest network and training.

In Indonesia and Vietnam, integrated ecologically-based rodent management was applied by farmers at a village level (70-100 ha) at two sites and normal management practices applied at two untreated sites for 2.5 years. The integrated management methods included:
promotion of synchrony of cropping (crops planted within 2 weeks of each other)
the use of a community trap-barrier system (cTBS)
short two-week campaigns to collect rodents at key times (1 week prior to transplanting; or within 2 weeks of crop initiation) and in focal (source) habitats,
where possible to reduce width of irrigation banks to less than 30 cm,
increase general hygiene around villages and village gardens.

The implementation and testing of integrated rodent pest management was based on a solid understanding of the population ecology of the pest species and of the farming systems, together with strong farmer participation. For example, in Vietnam, radio-tracking and monthly live-trapping indicated that rats used banks of major and smaller irrigation channels during the non-breeding season (tillering stage of rice) and used rice fields during the breeding season (ripening stage of rice). In Indonesia, monthly monitoring of rodent populations across five habitats highlighted that rats aggregated along main channel banks and in village gardens during land preparation. Farmers used this information to develop community-based rat drives along channel banks and around villages during the week prior to transplanting the rice crop or the two weeks after planting.

The integrated approach to rodent management provided strong economic, environmental and policy impacts.

Economic impacts: In Indonesia, there were consistent increases in rice yield (range 0.1 to 0.9 t/ha). In Vietnam, rodent densities were consistently low, however, there was marginally less rodent damage in the treated villages compared to the control villages.
Environmental impacts: There was marked reduction in chemical usage by farmers in the treatment villages. In Indonesia, at the beginning of the study 98% of farmers used chemicals to control rats across all sites. Often these were highly toxic chemicals mixed with oil and then Economic impacts: In Indonesia, there were consistent increases in rice yield (range 0.1 to 0.9 t/ha). In Vietnam, rodent densities were consistently low, however, there was marginally less rodent damage in the treated villages compared to the control villages.
Environmental impacts: There was marked reduction in chemical usage by farmers in the treatment villages. In Indonesia, at the beginning of the study 98% of farmers used chemicals to control rats across all sites. Often these were highly toxic chemicals mixed with oil and then added to the irrigation water. Two years later chemical usage had dropped to 46% of farmers in the treatment villages (with no oil "cocktails") compared to 88% of farmers in the untreated villages. In Vietnam, all farmers used chemicals across all sites. In the final year of the study, chemical usage had dropped to 4% of farmers in the treatment villages compared to 68% in the untreated villages. There was also a large reduction in farmers using plastic barriers around their crops in the treated villages (70% to 11%), whereas there was little change in the untreated villages (70% to 77%).

Policy impacts: In Indonesia, an integrated "National Rodent Management Program" (Gama Pamati) was developed in 2001 based on recommendations arising from collaborative work funded by ACIAR in West Java. This program now forms the basis for the national policy on rodent pest management in Indonesia.

In Laos, 10 research and extension staff from five provinces were trained at various times in the principles of rodent ecology and management. Projects were established in four upland provinces where data were collected on the history of rodent outbreaks, on breeding and species composition of the rodents, and on the effectiveness of a trap-barrier system (TBS) in the upland habitats. The TBS technology had limited impact in the fields in the upland shifting cultivation systems; however, farmers adapted the technology to protect their valuable grain stores from rats. A volunteer working with the project provided a high quality appraisal of the post-harvest impact of rodents in five upland villages, an assessment of different designs of grain stores and a detailed appraisal of the rodent fauna in forest habitats at one study site.

The first rodent taxonomic key was developed for all the significant rodent pest species and common non-pest rodent species in SE Asian. The key plus species distribution maps, photos of key physical features and a brief description of the biology of each species were published in ACIAR Monograph 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).

Australian studies of the field ecology of mouse populations have provided a better understanding of the key factors that influence eruptions of mouse plagues. The rate of change of populations during the breeding season is independent of density effects, but if the population density is high at the commencement of breeding then the litter size is depressed throughout that breeding season. There are density-dependent effects on survival during the non-breeding season. Moreover, rates of increase of populations over spring and summer are highly correlated with accumulated rainfall from the previous winter-spring (April-October). These findings have led to:

(a) A refinement of a model for forecasting plagues that has been used successfully in Victoria for the past three years.
(b) Development of a model on fertility control of mice that indicates that sterilising just one third of all female mice for the entire breeding season is sufficient to prevent mouse plagues. This detailed analysis of seasonal population dynamics has established specifications for the use of fertility control of mice that appear quite achievable.

The project had significant capacity-building outcomes, with 18 students undertaking research based on the project as part of their Honours or higher degree studies.