Rattus argentiventer Robinson and Kloss, R. exulans Peale, R. rattus spp., R. tanezumi
What it does
Rice field rats cut or pull up transplanted plants. They also chop young seedlings. At ripening stage, they feed on developing rice buds.
Why and where it occurs
Rats occur in lowland irrigated rice crops. Both the wet and dry seasons are favourable for rat reproduction and crop damage. In rainfed rice crops rodents have their greatest impact in the wet season. The availability of food, water, and shelter are factors, which provide optimum breeding conditions. The presence of grassy weeds also triggers their development.
Rice field rats feed at night with high activity at dusk and dawn. At daytime, they are found among vegetation, weeds, or maturing fields. During fallow period, they utilize major channels and village gardens as prime habitats. At tillering, 75% of time they are in burrows along the banks and after maximum tillering, 65% of time they are in rice paddies.
How to identify
Rat feeding can cause the following damages:
- missing germinating seeds
- missing hills
- chopped young seedlings
- missing plants
- irregular cuttings of stem
- chewed developing buds or ripening grains
- tillers cut near base at 45° angle
- retillering of stems
- delayed grain maturity
- missing grains
- missing panicles
The feeding damage on the stem caused by the rice field rats may resemble insect damage although rat damage is usually distinguished by the clean cut at 45° of the tiller. The damage on the grains is similar to bird damage.
- Check muddy areas for runways, active burrows, and footprints of rice field rats. These are usually near the damage they have created.
- Check for presence of rice field rats: cut tillers and active holes on the bunds that surround the fields.
- When possible, catch rats to identify the species. Place traps along runways, or dug the rats from their burrows.
Why is it important
Rattus argentiventer is the major agricultural rodent pest across much of island and mainland Southeast Asia. Crop losses in rice-growing areas due to this species are typically in the order of 10−20%. Losses are generally higher in the second crop in areas with double cropping.
For fields positioned close to refuge habitats such as canals or extensive upland areas, chronic losses of 30−50% are reported. Very high chronic losses are also reported in areas where triple cropping is practised and rat densities are especially high.
In Malaysia, this species has caused yield losses of 6−11%. In Indonesia, an estimated 17% of the total planted area is estimated to be damaged annually.
How to manage
Prophylactic measures are more efficient against rice ragged stunt virus than direct-control measures. Once infected by the virus, a rice plant cannot be cured. The use of resistant varieties for ragged stunt management is probably the most important control measure. There are three types of resistant rice varieties:
- resistant to brown plant hopper
- resistant to rice ragged stunt virus
- resistant to both, the virus and the plant hopper
Practicing synchronized planting is also a preventative measure. Infected stubble need to be ploughed- under after harvest to reduce the virus source.