Outflanking the Laotian Rice Thieves: CSIRO Scientists' Research on Mouse Plagues in the Australian Wheat Belt Is Helping Farmers in Asia Reduce Rice Losses and Other Damage from Local Rodents. Their Cunning Trap Barrier System Is Not Only Cheap, Simple and Deadly, It Also Greatly Reduces the Environmental Impacts of Rodenticide

Article excerpt

The impact of a rodent plague can be devastating. For example, a 1993 mouse plague in southern Australia cost an estimated AS 100 million in crop, stored grain and other losses.

In South-East Asia, it is common for villages to lose more than half their rice crop to rats. Sometimes whole crops are destroyed when rat numbers explode, or farmers don't even bother to plant, expecting that rats will eat the crop. As well as eating the crop, rats also eat young chickens and spoil grain.

CSIRO researchers have been studying mouse plagues in Australia since 1983, identifying the factors that trigger these events and how mice use different habitats at different stages leading up to a plague. This knowledge of mouse ecology now helps in managing outbreaks.

For the past 10 years, the CSIRO group has also worked on projects funded by the Australian Centre for International Agricultural Research (ACIAR) in South-East Asia. These projects have focused on identifying the rat species causing crop losses and developing integrated control programs appropriate to each locality.

South-East Asia has more than 418 species of rodents. Of these, 65 species are known to cause significant damage to crops. While three of these species are a threat to crops in Laos, the main culprit is the Black Rat, Rattus rattus.

Social differences in control strategies

Of 240 farmers from 12 villages surveyed at the start of the project, 233 said rodents were their main pest problem and caused most damage to rice and corn.

However, most of these farmers applied control methods after crop damage was apparent, rather than taking preventive action. Popular methods included trapping and hunting; cleaning up of weeds and other potential food sources and cover; cats; fumigation; and chemical rodenticides.

'One of the major differences between managing rodents in Australia and in Asia is the issue of scale,' says leader of the ACIAR projects, Dr Peter Brown.

'For example, in Australia, one farmer may manage thousands of hectares so it is easy to apply management over large areas, whereas in Laos and other South-East Asian countries, one farmer has only one or two hectares.

'We need to get more than 100 farmers or entire villages to work together in order to manage rodents at a sufficiently large scale. There is little point in controlling rats on one farm if all the neighbours do nothing.'

This adds an extra social dimension to working with farmers in Asia compared to Australia.

The initial survey showed that, while most farmers carried out rodent control individually, they recognised the benefit of working together. This was something the project enabled them to do.

Minimising'collateral damage'

Encouraging natural predators is an important part of any control program, says Dr Brown.

'In Myanmar (Burma), farmers introduced poison to control rats but the problem got worse because they also killed the natural predators.'

Most of the Laotian farmers used rodenticides as a last resort, as they thought chemicals were not safe. A Luang Prabang farmer reported that he had seen a decrease in the number of birds and snakes since applying rodenticide.

The ACIAR project aimed to educate locals about alternatives to rodenticide and involved about 50 farmers and extension workers, with control sites established in the fields and in villages.

The researchers introduced farmers to a control method known as the trap barrier system, involving erection of a plastic-sheet barrier around a small area of early planted crop. …