Introduction

• Rodents are one of the most important non - insects pests of agricultural crops, particularly rice. Out of 12 rodent species identified in India as the economic pests of agricultural crops, four appeared to be important in rice cultivation in Andhra Pradesh.

Types of rodents

• Lesser bandicoot rat: Bandicota bengalensis
• Field mouse: Mus booduga
• Indian gerbil: Tatera Indica
• Soft furred field rat : Rattus meltada
• Under irrigated conditions in coastal districts of Andhra Pradesh, Bandicota bengalensis and Mus booduga are the only two rodent pests associated with rice.

Damage at different stages

In India , rodents have been estimated to cause 5 to 10% losses in rice. Severity varies with season, location and ecosystem. Among the field crops, rice is the most vulnerable crop to rodents. In Andhra Pradesh the losses are estimated as 2 - 90%. Rodents do not spare any variety and they attack all stages of the crop during all seasons.

• In addition to tiller cutting, they also hoard ripened panicles inside their burrows. They have tremendous hoarding capacity especially in Bandicota bengalensis and Mus meltada. Hoarding by Bandicota bengalensis was observed in the farm at the time of harvest..

Nursery

• Maximum damage to nurseries takes place when the seeds are just germinated. At this stage, the nurseries are drained out and the rodents run freely inside the bed spoiling all germinated seed. Later, they also cut the seedlings 1-2 inches above the water level.

Main field

• Some times the rodents pull out the transplanted seedlings and create gaps in the main field. They start cutting the seedlings.
• Generally, their activity is confined to inside field leaving 2-4 meters on all sides of the field.
• In the initial stage, damage appears in patches and after some time, all these small patches become into one big patch. Damage increases with the onset of panicle initiation and continues upto panicle emergence.

Management of Rodents

• Rodent control is an age old practice and various methods are in vogue. However, there are very few methods which are practicable and feasible in situation like this.
• In Godavari delta, local traps called ‘ butta’ are extensively used for the control of rodents in rice. These traps provide fairly good results when applied after chemical control operation.
• However when directly used, trapping will be costly affair and one can not manage entire population over large areas. Moreover, at certain crop stages, like primordial formation, rodents are not attracted towards traps.

Natural Smoke

• Control of rodents living in burrows with natural smoke is an age old practice in India. The main principle involved in this operation is simply filling the burrows with smoke, which causes suffocation to rodents ultimately leading to their death.
• The smoke liberated by burning rice straw mainly contains carbondioxide. Now the Andhra Pradesh Agricultural University developed a ‘Burrow fumigator’ which is being used very extensively by the delta farmers.

Chemical Control Fumigation

• The fumigants like Aluminum phosphide is effective and widely used for the control of field rodents living in burrows.It was evaluated against Bandicota bengalensis in rice fields in Punjab,providing 66.6 % kill.
• The control of rodents using rodenticides is the more common way. There are two groups of rodenticides registered and available in our country. They are:
  • Acute rodenticides (Single dose and quick acting), Eg : Zinc phosphide.
  • Chronic rodenticides (Multi dose and slow acting), Eg : Warfarin, Bromodiolone.
• Acute Rodenticides: Among the acute rodenticides, Zinc phosphide and Barium carbonate are registered for use. Zinc phosphide is the only acute rodenticide available to control rodents.  

Action plan for Rodent control

Advantages of Zinc Phosphide

1. 1. Quick killing
2. 2. Small quantity of chemical is required
3. 3. Single feeding
4. 4. Population can be brought down immediately.

Disadvantages of Zinc Phosphide

1. 1. Necessity of prebaiting,
2. 2. Low killing around 40 – 50 %,
3. 3. Induce bait shyness.
4. 4. Toxic to non target species,
5. 5. Chances of secondary poisoning are more.

Chronic Rodenticides

• In order to overcome limitations and hazardous nature of acute rodenticides, lengthy baiting programme and possibility of resistance, new series of rodenticides have been developed and known as single dose anti-coagulants or second generation anti-coagulants. These rodenticides (Bromodiolone) combines better qualities of acute and chronic rodenticides.
• For effective and successful rodent control, the following programme should be adopted on large areas at a time on community approach.
• Chronic or multi-dose rodenticides (at present only anti-coagulants) are much safer than acute rodenticides because they are less toxic to the non-target species. But they have to be fed for 5 – 7 days to obtain desired results, which increases the cost of operation

Keeping in view the cost involved, simplicity and feasibility in field application, safety to human beings and non target species, weather and soil types, the following action plan is more pertinent or suitable for the control of rodents with bromodiolone concentration in rice fields of Krishna – Godavari deltas on community approach.

Day 1 Identify live burrows and place 15 g bromodiolone concentrate bait inside the burrow. Day 15 Repeat Bromodiolone baiting in active or live burrows. Day 16 Eliminate residual population through trapping or fumigation with burrow fumigator.

Principles

Grow same maturity group cultivars on large areas to restrict the availability of the vulnerable stage (Reproductive) of the crop. Reduce the number and size of the bunds, keep them clean to locate burrows and avoid harborage. Rodent control operations should be taken up on large area at a time. It checks cross infestation or migration of rodents from untreated fields to treated fields.

• All the control operations should be completed before the crop attains primordial initiation stage since at this stage the rodents are invariably attracted to the rice crop.
• Rodenticides should be made available before beginning of the season.

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