PreviousDespite taking all preventive measures, it will not always be possible to avoid infestation with rodents. Control measures are a basic requirement in keeping damage down to a minimum. The sooner control of rodent pests is undertaken, the better are the chances of success. Before any control measures are taken it is necessary to make a situation analysis.
11.7.1 Situation Analysis
In order to achieve the greatest possible success with measures to combat rodents, the following questions must be answered:
Correct planning of control measures can only be performed once these questions have been answered.
Depending on the degree of infestation, the following control measures can be used:
- Traps
- Cats
- Use of chronic poisons
- Use of acute poisons
11.7.2 Application of Non-Chemical Control Measures
11.7.2.1 Traps
The use of traps is only worthwhile if the degree of infestation is low. There are different kinds of traps. Distinctions are made between killing traps and arresting traps. When using traps, attention should be paid to the following:
11.7.2.2 Cats
Cats can make a contribution towards rodent control. It should be mentioned, however, that cats themselves may become a hygiene problem in stores if care is not taken.
11.7.3 Use of Chemical Means of Rodent Control
The use of rodenticides is only effective under good storage conditions and in particular good storage hygiene. Before the application of rodenticides, all preventive measures must be taken to ensure that no reinfestation takes place.
There are two groups of rodenticides:
Acute poisons are used only in the case of high rodent population with the aim of reducing the degree of infestation to a low level within a short period. Subsequently, chronic poisons or other methods must be used for further control.
11.7.3.1 Acute Poisons
- Properties
Acute poisons have a rapid effect due to their high toxicity, meaning that poisoned rodents die immediately. In control campaigns using these poisons the bodies of dead rodents can be found in and around the store. These must be collected and burned.
Acute poisons do not, however, work selectively. This involves a risk for other living beings. Therefore great care must be taken in applying acute poisons.
They must not be used in the same place again until at least six months have passed, as it will take this long for the rodents' bait aversion to be overcome (see section 11.7.3.5).
- Products
Zinc phosphide is the most common acute poison in use all over the world. It is comparatively cheap and has a good and fast effect it applied correctly. Zinc phosphide is mixed in bait in a concentration of 2.5%.
There are a series of other acute poisons, all of which, however have disadvantages compared to zinc phosphide and which are prohibited in many countries due to their side effects.
- Application of acute poisons
When applying zinc phosphide, follow all safety measures (see section 11.8) and proceed as follows:
975 g best quality grain + 25 g zinc phosphide
Before mixing add approximately 1% edible oil in order to prevent dust developing! (Never mix water with zinc phosphide!). Mix the bait by shovelling from one side to the other!
- Further measures
Continue the control campaign using chronic poisons or by putting out traps !
11.7.3.2 Chronic Poisons
- Properties
Chronic rodenticides have a delayed action. The rodents will die without feeling pain. They will thus not become suspicious of the poisoned bait and no bait aversion will ensue. Prebaiting is therefore not necessary. Poisoned animals normally die in their nests or hiding places. The bodies of dead rodents are therefore not usually found during the course of treatment.
- Products
· Anticoagulants
Anticoagulants prevent clotting of the blood. Animals that have been poisoned will die from internal bleeding. There are two different groups of these poisons:
"First generation" anticoagulants
These are rodenticides which only lead to death after repeated ingestion (up to 7 times). They are referred to as "first generation" anticoagulants because they were the first to come on the market. They include the following products:
| Active ingredient | Most common brand names |
| Warfarin | Warfarin |
| Difacinon | Ramik, Difacin |
| Chlorfacinon | Caid, Raviac, Quick |
| Coumatetralyl | Racumin |
| Coumachlor | Tomarin |
| Coumafuryl | Fumarin |
| Pindane | Pival |
"Second generation" anticoagulants
These are rodenticides which kill the animals after a single ingestion. These products are thus also categorized as "acute poisons with delayed effect.'. They include the following products:
| Active ingredient | Most common brand names |
| Brodifacoum | Talon, Klerat, Ratak Super |
| Difenacoum | Ratak |
| Bromadiolon | Rodine, Mak |
| Flocoumafen | Storm |
Bromadiolon is particularly used against mice.
An antidote in the case of poisoning with anticoagulants is Vitamin K', contained in plants. As rodent pests often eat weeds, the effect of the poisons may be neutralized. This encourages the development of resistance. Resistance is already present in a number of countries to Warfarin and other rodenticides. As all anti-coagulants work in essentially the same fashion, cross-resistances have developed even between the first and second generation anticoagulants.
· Rodenticides with hypercalcaemic effect
Calciferol (= Vitamin D2) works by triggering off a rapid calcification of the animals leading to quick death. One or two ingestions of the poison suffice for a lethal dose. Calciferol is very effective against mice and less so against rats. It can also be used in combination with other active ingredients, such as Warfarin.
There are rodenticides which have different :nodes of action. These include Bromethalin which incapacitates the animals' energy metabolism.
- Application of chronic poisons
When applying chronic poisons attention has to be paid to the safety measures in section 11.8. Proceed as follows:
Example for the preparation of a bait:
18 parts (900 g) of broken grain (premium quality)
1 part (50 g) of poison
1 part (50 g) of salt or sugar
Further measures
11.7.3.3 Formulations
There are various formulations of both acute and chronic poisons:
- Dust formulations
They are mixed according to the recommended application rate with a suitable feed such as cereal, to form a bait.
- Ready-to-use baits
Ready-to-use or prefabricated baits are available in various forms and compositions. They are used especially in the application of chronic poisons. The most common are:
- Tracking powder
This formulation is scattered on runs, in rat or mouse holes or other places frequented by rodents. When the animals run through the powder, some of it will stick to their feet and fur. Rodents clean themselves several times a day by licking their fur whereby the poison is taken in. Tracking powders can be used in combination with poisoned bait.
- Water-soluble powder
This poison is dissolved in water in the ratio of I part poison to 39 parts of water and offered to the animals as watering place. It is only recommended for use in arid regions where rodents are dependent on any sources of water they can find.
11.7.3.4 Bait
There is naturally no lack of food for rodent pests in a grain store. Bait has to compete with the other food sources. Attention should therefore be paid to the following remarks:
11.7.3.5 Setting out Bait
When working with rodenticides, danger to people, domestic and other non-target animals cannot be excluded. The following basic rule must always be observed:
Never set out bait in the open!
That means that bait must always be protected under some cover. This is in line with the rodents' preference for concealed places. Planks of wood, crates or bamboo tubes can be used. More suitable, however, are specially made bait boxes.
Bait boxes can be made from a variety of materials available locally. They should have an entrance and an exit on the opposite site as rodents do not like to enter dark spots. The openings should be approximately 6 - 8 cm in diameter for rats; 2 - 3 cm suffice for mice.
Care should be taken that the bait does neither absorb any moisture nor dry out. Bait boxes for placing outdoors should have legs and a waterproof roof in order to protect them from ground moisture and rain. A number of examples of bait boxes are shown in the following illustration:
When setting out bait, attention should be paid to the following points:
With rodents living outside the store (e.g. Norway rats, Bandicoot rats) place bait close to the inside walls of the store near the door and on runs outside the store! One bait station every 200 mē will generally be adequate. Around 300 g of bait should be used for every place.
With black rats, place additional bait in the area of the roof 3 bait stations every 200 mē are recommended with an amount of 100 - 150 g bait at each point.
For mice, set out numerous baits around 2 m apart in the store! An amount of around 50 g for each point should suffice.
- Leave the bait boxes in the same place for the entire duration of the control campaign! Any change in the location of feeding places would endanger the success of the campaign due to rodents' new object reaction.
11.7 3.6 Prebaiting and Bait Shyness
Prebaiting is essential when using acute poison! Due to the rodents' new object reaction they do not accept bait immediately. First one animal of the community will taste the bait only eating a little. When this bait is already poisoned the ingestion will not be sufficient to kill this animal but to make it ill. Poisoning with acute poisons causes pain. The animals are well able to recognize the bait as having been the cause of their pain and will avoid it in future. They will also pass on this information to the community, so that poisoned bait will no longer be accepted by any rodents and the control campaign will be a failure and have to be stopped. Once rats connect their sickness with the poisoned bait they will develop bait shyness or bait aversion.
Therefore prebaiting is practised which means offering the unpoisoned (untainted) bait until it is fully accepted usually after a few days. This is the moment when the poison should be added to the bait.
11.7.3.7 Keeping Records
A record must be kept of every control activity in the store journal The details should be listed on a separate control sheet. Enter the date when baits are set out. The amount of the bait which has been eaten should be estimated during inspections. On the basis of these entries decisions on the following points can be made:
An example of a control sheet is shown below:
Control Sheet for Rodent Control
Place:
Store No./area:
Bait Location
No./Ref.
Date of Control
Entries on the amount of bait eaten:
| Nothing eaten: - | Little eaten: x |
| Much eaten: xx | All eaten: xxx |
Person in charge of treatment:
Name:
Date:
Signature:
All safety measures for insecticides (see sections 8.4.1 and 8.4.2) also apply for rodenticides. Special attention should also be paid to the following:
"Danger" "Poison"
11.9 First aid measures in case of poisoning
The first-aid measures listed for insecticides (see section 8.4.3) also apply for rodenticides. Special attention should be paid to the following:
- Chronic rodenticides:
This group of poisons is regarded as having a relatively low toxicity. No symptoms or damage will normally result from a single ingestion. Nevertheless, always consult a doctor on suspicion of poisoning.
Anaemia and shock may occur with repeated ingestion of chronic poison within short time.
Vitamin K1 (5 - 10 mg) can be administered as an antidote.
A blood transfusion is necessary in serious cases of poisoning.
- Zinc phosphide
Anyone suffering from zinc phosphide poisoning must be taken to the nearest hospital immediately!
Symptoms of poisoning are catarrh of the throat, bronchitis and possibly pneumonoedema, and with serious poisoning sickness, vomiting (smell of carbide) diarrhoea, disturbance of consciousness and cramps.
The person affected should be made to vomit immediately by sticking your fingers deep into his mouth. Potassium permanganate solution (0.1%) as well as activated carbon should then be administered.
The following equipment is required for dealing with rodents:
ANONYMOUS (1983)
Food Storage Manual, FAO, Rome, 263 pp.
ANONYMOUS (1980)
Post-Harvest Problems, GTZ, Eschborn, 258 pp. + 33 pp. appendix
BUCKLE, A.P. & R.H. SMITH, ed. (1994)
Rodent Pests and their Control, CAB international, Wallingford,
405 pp.
POSAMENTIER, H. & A. VAN ELSEN ed. (1984)
Rodent Pests and their Biology and control in Bangladesh, Dhaka,
111 pp.
WEIS, N., ed. (1981)
Rodent Pests and their Control, GTZ, Eschborn
