While rodenticide resistance is not a widely discussed issue or problem in North America, pest management professionals (PMPs) should be aware of the potential threat of resistance to certain rodenticide formulations. Rodent resistance to the single-feeding anticoagulants bromadiolone, difethialone and difenacoum* is an alarming problem in Europe — and PMPs should stay educated about resistance, especially because single-feeding rodenticides are so widely used in North America. Knowing the signs of resistance, and learning how to proactively prevent resistance, can help deter this issue from becoming a problem over here.
If you have been baiting and continue to find droppings in cabinets, pantries and other food storage locations, hear squeaks and scampering throughout the house and see nibble marks on food, food containers and furniture, your bait might be ineffective. Oftentimes, however, it is not the active ingredient that is ineffective. Rodents can simply become less attracted to different bait formulations — and will not eat the bait because of the taste or consistency.
Here are a few suggestions to ensure a successful rodent control program:
• Use non-chemical control methods. Examples include traps, sanitation programs and rodent-proofing.
• Learn the habits of the rodent population. Avoid using first-generation (multiple-feeding) anticoagulants in areas with suspected resistance.
• Consider environmental factors. When selecting a bait, be knowledgeable about how to use it and the possible effects it may cause.
• Ensure complete eradication. Conduct thorough inspections, timely follow-ups and ongoing monitoring programs whenever a rodenticide is used.
• Remove other food sources. If food is somewhere other than where the bait has been placed, rodents may not be eating the bait. Try to ensure that the bait is the only food source near the infestation.
• Change the bait matrix. While the active ingredient controls the rodent, it is the bait matrix that entices the rodent to consume the bait. So, it is important to select a bait that is highly attractive, making it difficult for rodents to detect the poison. In addition, alternate block bait and pellet formulations to entice rodents with different products.
• Plant bait in a high-pressure area. Be sure to place bait where you know rats and mice will be located, such as feeding areas and nests.
Homeowners do not want unexpected visitors, and PMPs should not have to continuously address rodent infestations. By following these steps, your rodent control program will help wipe out pesky mice and rats — leaving your customers satisfied with a rodent-free environment.
*Author’s Note: At press time, there have been no documented cases of resistance to brodifacoum.