[Vertebrate Pests] Building Perimeter Surfaces and Pests

In my July 2004 Vertebrate Pests column “Landscaping and Vertebrate Pest Issues,” I discussed how certain landscaping shrubs and bushes planted around building exteriors can be conducive to attracting and/or harboring rodents, birds and urban wildlife. I discussed, for example, how bushes that form dense globes close to the ground can be utilized by city animals in a multitude of ways.

But creating a building exterior (or modifying an existing one) to minimize attracting and harboring pests around the exteriors of commercial buildings doesn’t end with shrub selection. The actual perimeter surfaces (e.g., mulch, stone, grass, etc.) next to a building into which shrubs and bushes are planted also play an important role. Perimeter surfaces can affect both pest pressures as well as what types of exterior rodent control equipment will need to be installed to protect the building.

Of course, it would be wonderful if property managers considered their building perimeter surfaces prior to landscaping — especially for clients such as office buildings, chain restaurants, grocery stores, warehouses, shopping mall exteriors and so forth. But most do not. And the majority of commercial landscapers do not have knowledge or expertise in low-pest pressure landscaping designs.

Obviously then, there are opportunities for pest professionals to advise and counsel commercial clients. Are some surfaces more conducive to pest issues than others? The answer is yes. A client could benefit significantly by knowing which building border is least pest-conducive. But as always, there are cost issues as well. Many of our commercial clients often opt towards the least expensive exterior landscaping designs, which often (and predictably) results in creating pest issues sometime later.

The most common types of building borders that are used in various combinations with shrubs, bushes and flowerbeds are: 1) decorative mulches; 2) crushed rock; 3) decorative pebbles; 4) turf; 5) cement slab borders; and 6) large rock motifs. (Note: In desert and semi-desert areas, sand, large rock, cacti and other materials are commonly used.) In general, desert motif landscaping is not highly conducive to rat and bird issues (but snakes, scorpions and ants are important pest considerations).

Of course, an important point to keep in mind when making building perimeter recommendations is whether or not your commercial client is a food-handling establishment (e.g., a chain fast food restaurant vs. an office building, a non-food warehouse, etc.).

Certain perimeter surfaces such as bare soil and mulch beds upon which food residues will be spilled are obviously also prone to offering breeding or attraction mediums for insect health pests such as filth flies, fruit flies, yellow jackets and others.

So, let’s examine the following various building perimeter surfaces as they relate to vertebrate pest issues.

MULCHES (FOR EXAMPLE, CYPRESS CHIPS, SHREDDED OR OTHERWISE)

• Visually attractive when fresh.
• Has earthy, natural look; appealing to most customers and employees.
• Inexpensive and fast installation to produce immediate results for rushed grand opening events.
• Absorptive base for any liquid food spills and odors, moisture retention from snow and rain, which produces food odors and or moisture to attract flies, rodents and other pests, yellow jackets, etc.
• Have to be periodically refreshed to remain aesthetically pleasing.
• Soft base allows for rat burrows.
• Over-mulching facilitates animal burrowing and concealment of burrows.
• The softness and insulative properties of mulch is highly attractive to many stray wild animals, to rest or burrow. 
• Absorb and hold stray mammal and bird excrement such as feces and urine (in addition to any rodents, also night foragers such as cats, raccoons, stray dogs, cats, etc.).
• It is difficult to remove and clean any discarded food litter embedded within the mulch.

CRUSHED ROCK

• Less vulnerable to animal burrowing activity. Also the harder rock surface is less attractive to wildlife.
• Fewer change outs required than mulch.
• Crushed rock borders should measure about 2-3 feet wide and be about 4-6 inches deep.
• More expensive than mulch.
• Food spills or grease spills particularly unsightly and unsanitary.
• Less aesthetically pleasing to the eye than mulch or pebbles.

DECORATIVE PEBBLES

• More expensive choice than others, but offers perhaps good return and low pest vulnerability.
• Highly attractive; clean appearance.
• When combined with island motif of non-cave shaped shrubs or potted plants, it is one of the most widely used foundation schemes for both food and non-food facilities.
• Small pebble sizes discourage animal burrows. Pebble diameters of 1 centimeter or less are best.
• Decorative pebble borders should measure about 2-3 feet wide and be about 4-6 inches deep.
• Low cleaning maintenance. Trash sits on top of pebbles and is visible.
• Must be raked and kept clean.

GRASS

• Higher maintenance for mowing and maintaining weed-free during summer.
• Watering may be an issue during hot summer dry spells.
• High aesthetics. Ecologically appealing to the public; attractive; clean appearance. Most people enjoy looking at well maintained turf.
• Provides some cooling effects to building perimeters.
• Prone to both insect and animal pests; burrowing; or travel burrowing.
• Generally cost effective to clean and remove litter trash.
• Combined with island motif of non-cave shaped shrubs — another widely used foundation scheme in the food manufacturing industry.
• Cost effective for large warehouses and manufacturing buildings.

CEMENT SLAB WALKWAY-STYLE BORDERS

• High density cement perimeter (sidewalk) with large potted plants added for minor aesthetics.
• Borders’ widths and designs are subject to safety considerations, and must also allow for proper grades for water runoff.
• Long-term low maintenance return.
• Any potted plants added for decoration must be secured or they will be prone to vandals and theft.
• No seasonal issues as with turf or deciduous shrubs. 
• Easy to clean via sweeping and/or powerwashing.
• Appropriate for food manufacturing plants that produce exhaust fines from wall and roof vents.
• Highly prone to certain ant species nesting.

LARGE ROCK (BOULDERS) MOTIFS OR AS ACCENTS TO OTHER MOTIFS

• Large boulders must be monitored; animal pests burrow beneath, and insect pests such as ants find boulders attractive nesting zones.
• Up-front expense of large rock and transport.
• Low cost and low maintenance in the long term.

SUMMARY. Unfortunately, when it comes to reducing pest issues around buildings, pest professionals are brought into the picture after the fact (i.e., after a pest infestation develops). For instance, a big chain restaurant that is building six new stores in a new sub-development often bids out for all the components needed to get the stores up and running. Usually, landscaping is done last or close to opening day. The chain management often does not think of pest professionals as having a role in landscaping; (i.e., pests are pests, bushes are bushes). But we should be considered. So it can’t hurt for your company to make a suggestion at the same time you are invited to perhaps bid on those six new stores. Give them a fact sheet about shrub choices, perimeter surfaces and their relation to pest issues.

Educating your commercial clients on the importance of being pro-active (i.e, preventing pests from developing in the first place) always demonstrates progressiveness (one of the best qualities a professional pest management company can have). And beginning on the outside perimeter walls — the first line of our defense against pest invasions — makes so much sense.
 
The author is president of RMC Consulting, Richmond, Ind.