Rice

Rodent Management

Nature And Extent Of Damage

• Damage in the seedbed can be due to rats consuming seeds directly or pulling up germinating seeds later on. Rats cut or pull up recently transplanted seedlings. The rats cut or bend older tillers to reach the developing panicles. The eaten or chewed area on the stem may resemble insect damage.
• As the crop matures, rats cut or bend tillers to eat the ripening grain. Damaged tillers are cut near the base at a 45° angle.
• The rate or number of tillers cut per rat per night is high in the wet season and the vegetative stage, lower in the dry season and ripening stage.
• Damage is usually low during the vegetative stage, increasing rapidly after the flowering stage.
• A low or moderate population of rats will cut tillers randomly throughout field. Damage will not be visible from a distance until more than 15% of the tillers are cut.
• When high rat populations occur, damage may be concentrated near the centre of the paddy.
• Rodents damage rice crop in all the stages of growth. They may cut / up root newly transplanted seedlings.
• They cut diagonally developing tillers normally 5-10cm above the water level. The damage can be easily recognized, when tillers are thickened and possess hollow tubular cross section.
• Significant damage starts from the time of active tillering and it will be higher during early growth stages and decreases after heading (12 w.a.t.) when feeding switches over from vegetative tissue to the more nutritive panicles.
• The extent of rodent damage reported in India ranges from 0.44 to 60.00% of tiller damage.
• Patches of severe damage are visible within the fields, while some fields may appear to be undamaged, but possess evenly distributed damage. In all the cases border rows sustain little or no damage which might be a protective instinct.
• The damage patch distance from rice varies from field to field.
• In Tamil Nadu the distance varied from 1 to 16.6m (mean 8.33); 1 to 14m (mean 7.71m) and 1.5 to 12.6m (mean 4.65) respectively in Kuruvai, Samba, and Thaladi seasons.
• In addition to the damage to the tillers, rodents hoard the grain in their burrows in special chambers.
• The extent varies from 0.5 to 4.0kg per burrows.

Rodents In Rice

• Four species of rat are important pests of rice in Tamilnadu.
• They are the lesser bandicoot, mole rat or field rat Bandicota bengalensis, the grass rat Rattus (Millardia) meltada, the gerbil rat, Tatera indica and the Indian field mouse, Mus booduga.

Mole rat : Bandicota bengalensis

Description

• Heavy-built body, pig like face
• Dark brown colour with greyish white belly
• Thick short and harsh fur
• Scaly tail, averaging 80% of head and body length
• One per burrow

Grass rat : Rattus (Millardia) meltada

Description

• Body small and slender
• Colour – Dark brownish grey above and pale grey below with soft fur
• Tail little shorter than the body length
• Moderately to poorly haired
• Tail may slough off.
• One per burrow, burrow smaller

Indian Gerbil rat : Tatera indica

Description

• Body large, sandy brown to reddish grey with white underside
• Tail longer than the body length
• Well haired, tufted with a stripe on each side
• Terminal tuft black in colour

Indian field rat : Mus booduga

Description

• Body – very small, brown in colour with white belly
• Tail shorter than body length, tail is dicoloured dark

Monitoring

• Rice land rats spend the daytime in vegetation, weeds, or maturing rice fields.
• They are not readily seen; only their runways and foot prints in muddy areas are visible.
• The general level of rat activity in a rice field can be observed by inspecting the area for signs of activity.

Rodent Management

Field

• Dig burrows and kill rats at the beginning of crop season while rectifying bunds for cultivation,plan to have narrow bunds in the field which are inadequate for the rats to construct burrows.
• Avoid keeping hay stacks near the fields as they provide excellent harbourage for rats
• Set up indigenous local rat traps like bow traps at the rate of 20 to 25 per acre.
• When rat infestations are widespread, use an acute or single dose poison like zinc phosphide
• Immediate follow up of the baiting process with mutidose or chronic anti-coagulant rodenticides: Food material 450g, any edible oil 10g, powdered jaggery 15g, anticoagulant rodenticide like warfain 0.5% 25g or bromadiolone 0.25% 10g. Continue the baiting process with anticoagulants until the rat damage becomes negligible.
• Prepare bait material with local food material preferred by the rats: Food material 97g, any edible oil 1g, zinc phosphide 2g.
• Before providing the poisoned zinc phosphide, keep plain or non-poisoned bait for two or three days to make the rats get used to the food provided. Provide such bait stations in about ten places in an acre.
• Make sure that the rats have started accepting the plain food and replenish with more food.
• During the process of baiting with rodenticides, the rats can also be controlled by fumigating the burrows with aluminium phosphide pellets.
• Plug the entry holes of all rat burrows in the late afternoons
• On the next morning, locate the burrows which have their entrance opened by the rats and insert two pellets each of 0.5 or 0.6g of aluminium phosphide per burrow.
• Insert the pellets as deep into the burrow as possible and plug the entrance with a mud ball.
• Ensure that all emergency exists of the burrows are also well plugged with mud balls so that the phosphine gas released from the pellets will have a good kill of the rats inside the burrows.
• Encourage natural check of the rats by not killing rat snakes, water snakes and other natural enemies of the rats and by providing perches on field bunds and fields for owls to encourage predation of rats.
• Soon after harvest, organize campaigns to dig out rat burrows and kill them.

Note:

During summer months, the food is scarce in the field and rats will accept the offered baits readily.

Godowns

• If rodents are noticed, bait them with multidose or chronic anticoagulant rodenticides as detailed above.
• Keep them in small cups on the rat runs, dark places, etc. where rat frequently move.
• Replace consumed bait daily.
• Collect the rats which begin dying after 5 or 6 days and bury them.
• Use also water soluble bait by mixing 25g of water soluble coagulant in 475ml of water and keep them in shallow cups or plates in a number of places inside the godown for the rats to drink the poisoned liquid and get killed.
• Use the same material stored in the vicinity for preparing baits and to make the rats to accept and eat them without suspicion.
• Once the rat population has been contained, discontinue the baiting or remove all the baited food and destroy.