Effective rodent management relies on the ability to identify signs of an infestation, interpret site-specific rodent activity and overcome the cryptic, exploratory and opportunistic behaviors of rodents. But what if indoor mouse and rat problems could be prevented? To achieve this, a new movement within the pest management industry is cashing in on an old idea: exclusion.

RAISING THE BAR. Customers in today’s market are well educated and many are looking for “safe” pest management alternatives. With high (sometimes unreasonable) expectations, customers are apt to switch service providers if even one pest is observed. To address this new market, some companies have raised the bar by offering proactive services to prevent pest problems over the long term. When done correctly, this requires a skill set that is not traditionally found within the pest management industry, because proper exclusion requires the selection of appropriate construction materials and application of correct techniques. The company that offers expertise in exclusion will have an advantage in the current business climate. Is your company ready for this revolution? The topics that follow will help you get started.

REASONS FOR ENTRY. Before we discuss the ins and outs of exclusion, we should first understand the factors that motivate rodents to enter buildings. A consideration of what pests need to survive says it all: rodents enter buildings in the pursuit of food, water and shelter. Air currents may have seasonally appealing temperatures (cool in the summer, warm in the winter), or carry the scent of food items being prepared inside. At a more basic level, the gap under a door or opening around a utility pipe mimic natural openings that could provide resources. They are worthy of exploration.

If the size is right, outdoor holes and openings can lead rodents indoors.

IDENTIFY THE GAPS. Knowing that openings are an invitation to rodents, the first step in an exclusion program is to identify gaps. Some of the most common entry points include utility lines that penetrate the building envelope (water, electrical, etc.) and openings associated with doors. Indeed, we learned in an August 2015 PCT article by Dr. Bobby Corrigan that there is more to doors than the opening at the bottom. (See “references”.)

To identify the gaps, conduct inspections that cover all exterior portions of the building, including rooflines. Bring a ruler: crevices ¼-inch high, or round openings 3/8-inch wide, permit mice, while rats can squeeze under ½-inch openings and through ¾-inch-wide gaps. Look for sebum and droppings around openings. Also look for chew marks — and know that pairs of teeth from mice are 2 millimeters wide and 4 millimeters wide from rats.

Inspections should not be limited to the building exterior. It has long been known that pests move within and between units of a building via shared walls (Runstrom and Bennett 1984), so inspections should identify internal pathways. Knowledge of building construction is useful here. For example, balloon framing creates a void that runs from the sill plate to the top of the structure.

SEAL THE GAPS. Here is where it gets challenging. As a pest professional, you are uniquely qualified to find openings that permit pest entry. And while experts agree that exclusion is the future of pest management, expertise in the field remains somewhat limited. Specifically, the selection and use of appropriate materials is critical for effective pest exclusion, but few published resources are available that provide recommendations and instructions. Further, recommendations may not be based on scientific evidence, putting into question their validity.

The technical document “Pest Prevention by Design” offers information about products that can be used in specific circumstances to exclude pests, rodents and otherwise. This includes recommendations for the thickness of sheet metal and concrete, or the correct gauge to use for woven hardware cloth. Additionally, articles written by Dr. Corrigan provide insight about sealants (and the important difference between these elastomeric products and caulks, which are not well-suited for pest exclusion), escutcheon plates (Corrigan 2008) and doors (Corrigan 2015).

A vegetation-free zone (2-foot band, 6 inches deep using stones smaller than 1 inch) is ideal for rodent exclusion.

THINK PERMANENCE. Products will inherently vary in their ability to withstand pests. However, a critical point to consider is that items sold for weatherization are not suitable for rodent exclusion (but may help against crawling insects). Indeed, most door sweeps sold at hardware stores can be overcome by a single rodent. On the other hand, high-density brush sweeps or rubber encased steel fabric sweeps can be used to keep rodents out (Corrigan 2015). Pest pressure will dictate which type of sweep you select: areas with large rodent populations, or those with rats, will want to use rubber-encased, steel fabric sweeps.

Expanding foams are designed to make buildings more energy efficient, and are not appropriate for rodent exclusion. Instead, small gaps (1 inch or less) can be filled with steel fabric mesh fit snugly to prevent removal. Openings of all sizes, especially those larger than 1 inch, should be sealed with sheet metal, concrete, woven hardware cloth or other aesthetically appropriate, permanent materials. Importantly, these items must be affixed to the surface properly to prevent edges from bending. Keep in mind that one-product-fits-all solutions do not exist and professionals will need to utilize multiple, site-specific materials.

REMEMBER PERMEABILITY. A mistake that is easily made with rodent exclusion is to completely seal a structure. However, some structural materials or building features are designed to accommodate airflow, water drainage and building movement. “Sealing” these structures can lead to new or additional problems, such as moisture issues, that will degrade the integrity of the building. Thus, water-permeable materials are needed for weep holes, breathable materials should be used on soffit and ridge vents, and woven hardware cloth can be used on air vents.

WHERE TO START? A question that often arises when considering pest exclusion is where to start: reduce pest populations or implement exclusion? There is general agreement that population reduction should occur before or at the same time as exclusion. The alternative of performing exclusion first could trap rodents in a building and could lead to more damage.

Vegetation in contact with a building provides “bridges” that offer access to pest harborages.

Exclusion should be performed in a systematic way that is informed by your inspection. Minor pathways that are seldom traveled by rodents (no droppings, chew marks or sebum trails) should be sealed first, while primary pathways in the building should be targeted for population reduction (trapping) then sealed, once the population has been reduced.

MINIMIZE ‘BRIDGES.’ Vegetation in contact with a building, or plantings adjacent to the foundation, provide bridges that offer access to pest harborage. Thus, vegetation management is an important, but often overlooked, component of rodent exclusion because pest professionals lack the tools, expertise or certifications required to perform the work. Homeowners or building managers may not follow recommendations to prune branches 6 feet from a home, prune low-growing plants to a vase shape, or install a vegetation free zone (2-foot band, 6 inches deep using stones smaller than 1 inch). Therefore, these services could be incorporated into an exclusion program, providing the proper licensing is obtained.

OPPORTUNITIES IN EXCLUSION. Naturally, the concept of exclusion applies to more than just rodent pests. In fact, it is commonly stated that exclusion is the preferred method to prevent problems with overwintering insects and occasional invaders because these pests are considered a problem only after they enter structures. Exclusion can be used to eliminate cracks and crevices that provide harborage for cockroaches and bed bugs, limiting inspection time and enhancing the success of management techniques. New technologies such as sealants, particle barriers and mesh screens designed specifically for the pest management industry are now available to address termite and fire ant problems.

Regular inspections are necessary to verify buildings or pests didn’t create any new gaps.

As the industry continues to adopt pest exclusion, progressive companies have created new divisions that cater to this expanding niche market. To be successful, firms should seek employees with a background in construction, who are able to provide site-specific solutions. Of course, exclusion work is more costly in materials and time, which should be reflected in rates.

THE TIME IS NOW. Pest exclusion is an old idea, but one that is finally gaining traction in the industry. Companies that specialize in exclusion may have an advantage for providing long-term, effective methods of keeping pests out. Remember that long term does not mean one-time service. Regular/annual inspections are needed to verify that products are holding up, that buildings have not settled creating new gaps, and that pests have not created their own openings. In this way, pest exclusion may represent a high-level, routine service, and one that might represent the future of pest management. The time to research, experiment with and implement exclusion practices is now.

The author is a pest management specialist in the New York State IPM Program at Cornell University.

References
Corrigan, R.M. “Recommendations for Selecting and Using Caulks and Sealants in Pest Management Operations.” RMC Pest Management Consulting Richmond, Ind.
Corrigan, R.M. 2008. “Escutcheonology 101.” PCT Magazine, GIE Media, Richfield, Ohio. February.
Corrigan, R.M. 2015. “Of Rodents and Doors 101.” PCT Magazine, GIE Media, Richfield, Ohio. August.
Runstrom, E.S. and G.W. Bennett. 1984. “Movement of German Cockroaches (Orthoptera: Blattellidae) as Influenced by Structural Features of Low-Income Housing.” Journal of Economic Entomology 77: 407-411.