TIMING OF COMMUNITY RAT CONTROL—EARLY ACTION IS MOST EFFECTIVE, WHEN RATS ARE NOT BREEDING

Rodents take advantage of favorable conditions to breed very quickly. In Indonesia, Malaysia and Vietnam, in lowland irrigated rice, the rice field rat breeds when the rice crop is at the late vegetative stage. If there is one crop per year the rats breed once; if there are two crops per year, the rats breed twice. Usually, the rats will only produce two or three litters per cropping season, none of which will breed in that season.

The removal of one female rat before she breeds is equivalent to killing 35 rats when the crop is at the ripening phase.

Planting crops more than two weeks apart – a recipe for disaster
If neighboring crops are planted more than two weeks apart, the breeding season will be extended long enough for the first litter to have time to breed, resulting in an explosion of population numbers.

For example, consider a three-week extension to the harvesting period because crops are not planted at the same time. A single female breeding early in the season can give rise to as many as 120 rats feeding on the last crops to ripen.

Traditionally, rodents are only controlled when their numbers are high. This is probably the worst time to deal with the problem!

Note that the major pest species of rat in the Philippines, Laos and parts of Cambodia is different and they are able to breed during most of the year. However, their peak of breeding coincides with the maturing rice crop. So again, early action is the most effective.

In South Asia, the situation is more complicated because of different species of rodent pests. However, the principle of matching control action to the breeding ecology of the rat still applies.

Further reading:

Singleton, G.R., Sudarmaji, Jacob, J. and Krebs, C.J. (2005). Integrated management to reduce rodent damage to lowland rice crops in Indonesia. Agriculture, Ecosystems and Environment 107, 75-82.