Prevention is better than cure! Rodent pest management measures are to create environmental conditions which discourage rats from entering and becoming established in buildings and increasing their population. Often farmers do not take action until damage is obvious. At that stage:
Situation analysis: Prior to taking any action, the situation should be analysed, taking account of the different types of agricultural systems, synchronised or continuous harvesting and the movement of rodents between fields and villages.
Regular observation: Continuous surveillance of an area is by far the most important and effective management technique. The earlier the presence of rodents is observed, the cheaper and simpler any subsequent action will be and losses will remain negligible. In addition, the store is monitored for possible points of entry (i.e. broken walls) or for potential shelter (i.e. discarded bags in a corner). It should be pointed out to farmers and storekeepers that each day rodents infest a store unnoticed more individuals are able to enter and food loss increases irretrievably. Family members, women and even children in small farming households should be motivated to check for the presence of rodents or damage each time the store is visited. For larger stores, someone should be made responsible for checking the conditions at least once a week, preparing a short report on the observations and any follow-up action taken.
This type of monitoring not only determines where the rodents come from, but also makes the people involved more aware of the problems and benefits. It also demonstrates the simplicity of managing rodent pests.
With some experience, it is fairly simple to check whether rodents are present. Occasionally, traps can be set to establish the species present, which provides information relevant to control. The presence of rodents can be noted through droppings (identification needs some experience) and minor damage such as broken bags, gnawed structures, burrows and holes in the floor or just outside the building. Tracks regularly used by rodents become stained ('smears') and can also be observed; however, infestation should never reach that stage.
Sanitation: It is much easier to notice the presence of rodents if the store is clean and tidy. Regular sweeping serves four functions:
In large stores, a strip of about one metre from the walls should be kept clear. Produce, and especially grain, should be kept in bags away from the floor. Equipment and materials should be removed or neatly stacked. The area outside the building should also be cleared of weeds and materials as far as possible because rodents are secretive and avoid open spaces. Finally, overhanging branches should be removed to prevent climbing species entering the building through the roof. In villages, any feed for domestic stock, particularly chicken feed, should be removed and should not be left lying around after dark.
Farmers should be made realise that the benefits of hygienic practices also apply to the field situation. Keeping dikes between fields small, the vegetation short and removing unnecessary vegetation will reduce the rate of infestation and make the presence of rats more easily noticeable.
Proofing: This somewhat unusual term means that a building should be made rat-proof in order to discourage rodents from entering. To do this, common sense should be used. Some species are very good climbers and rain pipes or rough vertical surfaces are no barrier. Small mice can enter through cracks as little as one centimetre wide. Doors should be kept closed when not in use and cracks and holes should be repaired at all times. Therefore, it is important to know the type of species involved.
Trapping: Trapping may be used if operators do not want to or cannot use poison because it will cause contamination. Near humans, rats are wary of traps and some will not enter them. With experience, it will become clear which locations are good for placing traps.
Rodenticides: Poison bait should only be used if rats are present. In stores or buildings, it is suggested to use single-dose anticoagulant poisons, preferably as ready-made bait. It should always be applied according to the manufacturers' recommendations. Operators should be strongly advised of the negative effects of over- or underdosing. Rats may not take the poison or receive a sub-lethal dose. Wrong dosing is a common practice. Farmers hope to save bait or to improve control, but unfortunately, it does not work that way!
Operators should be aware of the fact that rodenticides are poisonous to most animals, including humans and domestic stock, and contact with rodenticides or contamination with the produce must be avoided. Finally, dead rats should be removed and kept away from other animals in order to avoid secondary poisoning.
Bait should be placed both inside and outside buildings frequented by rats. If domestic stock has access to the baited area, bait containers, which are protected baiting points, should be used.
If rodent pressure is high (in stores after harvest), the pulse baiting technique is most efficient. Using this technique, bait is placed for 3 days and discontinued for 7-10 days. It takes rats up to 10 days to die. Therefore, bait is placed again about 14 days after the first session. This is repeated until the population has reached very low levels. This method is just as effective as continuous baiting and actually saves bait. The time taken to reduce the population depends on its initial size in and around the building and on the amount of immigration. It is important to continuously monitor the situation. The operator will quickly learn what amount of bait to use and the best locations for baiting points.
Operators familiar with fumigation can also use gases to kill rats. Hydrogen cyanide or aluminium (magnesium) phosphide tablets are applied to a burrow system which is then closed. However, this is only effective in very compact soils. It is a dangerous method and should only be applied by well-trained and licensed operators, not by farmers!
Contact dusts and tracking powders are poisons spread on the ground. Animals pick them up on their fur and ingest them during grooming. This method is used against mice which are not easily attracted to bait stations. However, it should only be used where food cannot be contaminated by animals carrying the poison.
Cooperation: The larger the area managed or controlled with poisons, the more effective the impact. Farmers should be helped coordinate activities, for example, neighbouring farmers could conduct rat control measures simultaneously. The health ministry and extension department should aim to coordinate activities near villages and cities.
Predation: Experiments in Bangladesh and Myanmar have shown that village households which keep a cat have fewer rats than others. This is not related to predation, but to the fact that the presence of cats makes rats and mice nervous and keeps them away.