October 2023 Issue by John Moore, MSc

 “The best offense is a good defense."

This quote is accurate when considering rodent control. Rodent control efforts are only marginally effective if pest exclusion is not the primary component of a rodent control program. Yet, it is often last on the list of things to do when dealing with a rodent infestation. A robust pest exclusion program can be time-consuming and, at times, costly. However, adding traps, rodenticides, and other monitoring devices to our structures is also costly and time-consuming and really does not offer a solution to the problem. Continually harvesting rodents inside of the structure does not solve the problem because we have not stopped them from coming in.

This time of year, the exterior pressure from many pests (especially rodents) to get in our structures is high for a couple of reasons. Rodents (like us) need food, shelter, and warmth. These 3 needs become harder to get as the season changes. These needs are precisely what our structures have, which is why they are so attractive to rodents. They will go to great lengths to get in. Excluding them is your best defense and solution.

What do we mean by exclusion? Let us look at rats and mice and their abilities to penetrate the structure.

Mice - crevices ¼-inch high, or round openings 3/8-inch wide, permit mice entry. They are excellent climbers and can often find these gaps along the roofline or on the roof itself as well as ground floor.

Rats - can squeeze under ½-inch openings and through ¾-inch-wide gaps. They are also good climbers and can enter the structure up high as well as the ground floor.

Any exclusion efforts should focus on these types of gaps and openings from the roof to ground level. This can be a daunting task, but take the easy ones first like doors, foundation gaps/cracks, utility penetrations, and vents. Doing a thorough job of exclusion at ground level can significantly reduce rodent numbers making it inside. Spray foam is a popular material to use because it is fast and inexpensive. However, the spray foam does little to deter rodent entry as they can and do frequently chew through it and, in some cases, will live in a hollowed-out section. Instead, think more about permanence when using exclusion materials like rodent-proof door sweeps, concrete, steel wool or copper mesh, hardware cloth, or specially designed sealants made to deter rodents.