Know your actives

Thursday, 25 April 2013 09:10

    Going back 20 or 30 years the range of rodent baits available may have seemed a lot simpler – so why have things changed so much and which product should you use and when? The technical team from leading British manufacturer PelGar International sheds some light.

    Selecting the right tool for the job is essential in getting the best results. Not surprisingly the same applies to product selection in rodent control, and an understanding of the differences between the various active substances will help you make the right product choice for effective rodent control.

    The UK industry focuses on two main active substances; difenacoum and bromadiolone. Both are second generation anti-coagulants and, to ensure the ingestion of a lethal dose, both require the target rodents to eat more than a single meal. They are therefore referred to as multi-feed baits. Understanding how much rats and mice eat each day, and what lethal doses are needed for effective control will help to give a better understanding of which products are best used in different situations.

    A rat will typically eat 25-30g of food in a day, which is taken in about ten small meals, with a maximum consumption per meal of around 3g. Rats are inclined to ignore food sources which are situated in ‘exposed’ locations and if the food is ‘free’ will retrieve it to a place of security and ‘stash’ it there. Mice on the other hand are exploratory feeders and will consume around 3g of food in a day but in many small meals – with a maximum meal size typically around 0.2g. As such, for a bait to be considered as a single feed, the lethal dose must be below 3g of bait for rats and 0.2g of bait for mice.


    Table 1: Quantity of finished bait required to generate an LD50 (average lethal dose) in rats and mice

    ActiveTrade namesBait Concentration (PPM)LD50*(g of bait) Brown RatLD50*(g of bait) House MouseApplication
    DifenacoumRoban, Neosorexa509.00.4indoor and outdoor
    BromadioloneRodex, Slaymor, Tomcat505.60.9indoor and outdoor
    BrodifacoumVertox, Jaguar501.40.2indoor only
    FlocoumafenStorm501.30.4indoor only
    DifethioloneRodilon255.61.3indoor only

    Data taken from industry standard figures. LD50 values are shown in grams (to 1 decimal place) for 250g rats/25g mice.  The concentration of active in the baits is the standard commercial rate for that active.


    From this we can see that rats could consume a lethal dose of difenacoum, bromadiolone, and difethiolone in around two to four meals, confirming their status as multi-feed baits. Depending on the quality and palatability of the bait formulation then all of these baits can provide a good opportunity for the target pest to consume a lethal dose within one day of feeding, and commonly rats may ingest several lethal doses over the first two to three days of feeding before ill effects are felt. Brodifacoum and flocoumafen are true single feed rodenticides against rats. The data also indicates that difenacoum is by far the most effective of the multi-feed baits against house mice and, when its non-target toxicity profile is considered, should be the product of choice for mouse control. The only true single-feed product for mouse control is brodifacoum.

    Difenacoum, because of its remarkable specificity to commensal rodents, has one of the best toxicity profiles of the anticoagulant rodenticides and has been shown to have reduced toxicity to birds and as such has merit for rat control programmes in sensitive outdoor situations such as those where non-target species e.g. birds of prey are in residence. The table below, where figures are available, gives an indication of the toxicity profile of the above rodenticides to non-target animals. These figures should be taken as an indication only; rodenticides should always be protected from non-target animals and in any case of accidental or secondary poisoning you should always consult a vet or doctor.


    Table 2 – Non-target toxicity – LD50 grams of bait per kilo of animal


    Data taken from WHO and The Pesticide Manual (BCPC)


    The figures show that there is a very real difference in the toxicity profile of the different active substances to non-target vertebrates. By comparing target species toxicity with non-target species toxicity a measure of risk can be determined. For instance, flocoumafen and brodifacoum are around six times more effective against rats when compared to difenacoum, though when considering they pose a threat at least 50 times higher to dogs (as an indicative non-target species), the products become considerably less appealing.

    Understanding and choosing the right active substance for the job in hand is vitally important due to the significant variation in activity they have against rats and mice and the toxicity to non-target animals. Formulation choice is also important in any rodent control campaign as the rodents must first find the bait and consume a lethal dose. No rodenticide or formulation is completely universal and selecting the right product for a job will minimise environmental risk and save time and money.

    (For further help and advice order free copies of PelGar’s ‘Six Steps to Successful Rodent Control’ DVD along with its detailed staff training guide. Call 01420 80744 or e-mail [email protected])

    About Us

    PelGar International was incorporated in 1995 to develop and supply innovative and novel rodenticide and insecticide products to the global public health pesticide market. PelGar believes that, while the active ingredients used in the industry are common, the target pests and the environment in which they live are very different. Providing cost effective control therefore means that the active substance needs to be available in a wide range of formulations and this is where PelGar’s expertise lies.

    Contact Information

    • Address: PelGar International Ltd, Unit 13 Newman Lane, Alton, Hampshire, GU34 2QR, UK
    • Tel: + 44 (0)1420 80744
    • Fax: + 44 (0)1420 80733
    • Email: [email protected]
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