We are often asked which poison the homeowner should buy in order to deal with a rat or mouse problem within their house.
They ask if they should buy the blue stuff or the red stuff, if pasta is better then blocks?
There is also an assumption that the poison I buy is stronger then what is available to the amatuer.
The answer to the above three questions is, the colour is never an indicator of the poison's potency or effectiveness, neither is the form that it comes on, whether that be pasta, wax blocks, wheat or oats. There are 4 poisons which are readily available to both the amateur and professional.
So why would you pay a professional to do a job, when you could buy the same poison at a fraction of the price. It is fair to say that I could buy bricks, sand, cement a roof tiles, but I would never try to build a wall or fix my own roof. Dealing with a rat/mouse problem effeciently and effectively often requires lots of knowledge and experience. Pests are by their nature adaptive, and can often prove a difficult problem for the home owner to fix.... But thats enough of my ramblings, back to the questions...
Four Widely-Available Rodenticides
As we have already said, there are four main anti-coagulant rodenticides available, to understand which active ingrediant you are buying, a quick look on the packet will always give you the answer, its illegal to sell poison without it being clearly visible (althought sometimes the writing is small). But you will nearly always find it is Brodifacoum, Difenacoum, Bromadiolone or Diethialone. We will deal with them one at a time
However we must also understand the term LD50 - this information will not be readily available on the packaging but is vitally important in order to find the correct poison for your problem. The term stands for Lethal Dose 50%. It is the amount of that poison an aminal needs to consume per perentage of its bodyweight in order to stand a 50% chance of death under laboratory conditions.... Its morbib reading but as the stenght of poison isnt propotional for every animals and each poison effects the pets your likely to have in your life differently then we need to make sure you are reducng the risks as far as possible.
Brodifacoum - This is probably the 'strongest' poison you are likely to buy. It is a single feed bait, which means that the offending mouse or rat will consume a lethal dose at the first time of feeding. Its relatively fast acting with rats and mice dying within 3/4 days of consuming enough poison. There is very little resistence to it, but as we use more of this you can be sure that resistence levels will increase. Brodificoum is effective against rats, but also effective against dogs. So if you have dogs at home or dogs which visit, you need to be sure that they wont get access to this poison, or maybe consider using another.... We dont use this if dogs are on site....IN fact we use this very infrequently. We use this for house mice in city centres where the bait can be placed safetly in tamper proof boxes and concealed under kitchen unit kickboards, in kitchen cupboards or under floor boards where dogs cannot gain access. It is a good active ingrediant if you suspect the rats/mice are resistant to the poison you are using and need to change.
Difenacoum - This is one of the first 'Second Generation Anti - Coagulant' rodenticides' which was first made available in 1970's. It is a multi feed bait which means that a rat or mouse has to visit it several times over several days to consume a lethal dose. As a result it can take a little longer to deal with your problem. A rat needs to consume 9g to achive the LD50 we have already spoken about. Mice on the other hand only need 0.4g to achieve the required level for a LD50. We use the multi feed nature of this to encourage communal feeding in rats. As they feed other rats will see this and it encourages them into feeding. Dogs and Chickens need to consume close to there own bodyweight in order to stand a 50% chance of death in laboratories, while cats and pigs need to consume nearly double their bodyweight. Of all the poisons it is the least toxic rabbits, but it is still potent towards them needing to consume 40g per kg so care needs to be taken whichever poison you buy when being used around rabbits.
Bromadiolone - This active ingrediant is similar to difenacoum. It is twice as effective against rats but is till considered a multi feed bait which needs 5.6g for rats and 0.9g for mice to achive the required amount. It is very effective against pigs and alot more potent when consumed by cats and dogs. We often rely on this active ingrediant when clearing agricultural sites of large problems.
Diethialone - This active falls between the single feed and multifeed options. It is a strong poison but falls short of brodifacoum in terms of toxicity to rats and mice. There is no known resistence to this poison. Only one manufacturer produces this active ingrediant and the blocks they produce seem to be either accepted really well with a quick uptake or a total avoidance. It is the least toxic of all active ingrediants to dogs.
Formulations of Rodenticide
Rodenticide comes in numerous forms, the most commonly available to the home owner are pasta sachets, wax blocks and whole and cut grain. To help you decide which one your going to buy you need to consider the environment the rats/mice are living and other animals in that area.
Importance of Humidity
Humidity is a really important consideration. A wet area will cause whole wheat and cut grain to quickly spoil, wax baits on the other hand are more resiliant. Pasta sachets are really palatable to rats, but are also the most platable to dogs in my opinion. Slugs and snails seem to take great pleasure in destroying wax blocks but often struggle to get through the packaging of pasta or individual bags of wheat. Dry environments are often places to consider pasta sachets due to its higher moisture content.
And to deal with the last question - "why has the rat poison I've used not worked". If you've had all your bait eaten and still have a problem, it is highly likely that you need to put more poison down. When all the bait has been taken, it can often indicate that the problem was far larger then you imagined.
Further Resources
CRRU code of best practice will always be helpful. Think Wildlife has the most up-to-date legislation and will help you use your poison correctly and safely.
