COVER STORY: Trench Warfare

Authors’ note: As of this printing, Premise, Termidor and Phantom are not yet labeled for exterior-only or exterior-mostly applications. Companies should consult manufacturers and their state regulatory agencies for official opinions on such treatments.

Big changes are afoot in the war against termites. Until recently, baits were what caused many companies to rethink their service strategy. Who would have thought that liquids would once again be the hot topic throughout much of the pest control industry?

The new category of non-repellent liquid termiticides, represented by Premise® (imidacloprid), Termidor® (fipronil) and Phantom® (chlorfenapyr), has achieved a level of performance not seen since the days of chlordane. When applied in the traditional manner, retreats generally have been few and far between — enabling companies to sleep better at night knowing that treatments performed that day probably will be successful.

STILL IMPERFECT. Despite their effectiveness, conventional applications of any liquid termiticide leave something to be desired. Perhaps their biggest limitation is that they are invasive to property owners. In an effort to treat all conceivable avenues of termite entry, companies often are required to drill walls and floors, cut tile, move carpet and other furnishings, and apply large amounts of pesticide in places where people live and work. Treatment hoses, susceptible to breakage and leaking, are pulled through the building and drilling (especially indoors) can puncture utility lines and contaminate air-handling systems under slabs.

Increasingly, customers find these intrusions objectionable. In one recent survey, 93 percent of householders expressed concern about the application of termite control chemicals inside their homes (Potter and Bessin 2000). Although many of these problems can be avoided with baits, current baiting systems often are slower acting, more time consuming and in the long run, more costly to consumers.

THINKING ‘OUTSIDE’ THE BOX. While the traditional, drilling-intensive approach may be necessary with repellent pyrethroids and fast-acting organophosphates, it might be less crucial with some of the newer non-repellent liquids that inflict substantial termite mortality in the vicinity of treated zones. Based on the seemingly more forgiving nature of these products and their wider anticipated zone of effectiveness, we began investigating whether such compounds could eliminate termite infestations by treating primarily around buildings exteriors, in a manner similar to baits. Findings reported in earlier articles support this hypothesis (Potter and Hillery 2000, 2001, 2002) and some pest control companies have begun making perimeter-mostly applications, even though product labels do not currently support such uses.

The purpose of this article is to summarize what we’ve learned about exterior-targeted (perimeter) applications during the past four years. We also offer a perspective on the growing debate about such treatments and what they may mean to the future of termite control.

ONGOING FIELD STUDY. In 1999, we initiated a field study to see if termite infestations in buildings could be eliminated with non-repellent liquid termiti-cides applied exclusively around the outside perimeter. Fourteen structures in central Kentucky — 10 treated with Termidor and four with Premise — have been evaluated to date. The test has often been referred to as "the barn study," because some of the initial evaluation sites were large wooden barns for storing harvested tobacco (more than half of the structures in fact have been houses). Prior to treatment, all 14 structures were heavily infested with the Eastern subterranean termite, Reticulitermes flavipes, and had multiple areas of activity indicated by swarms, active mud tubes, infested structural wood and termites feeding in ground debris.

METHODS REVIEW. An important objective was to monitor the effects of an outside-only perimeter application on termites foraging in other areas, such as interior walls or entering through untreated expansion joints, cracks, voids or utility penetrations. To evaluate such effects, we used long-term monitoring stations in the manner used to assess the effects of baits on termite populations (Grace et al. 1996, Su and Scheffrahn 1996). Monitoring stations were located both below and above ground and on the interior and exterior of buildings. In-ground stations containing wooden blocks were established in areas where termites were feeding in cellulose debris or on wooden survey stakes. Above-ground monitoring stations, provisioned with cardboard, were established on walls, floors and structural members over active mud tubes. In still other areas, we used an acoustic emission detector (Locator®) or microwave device (Termatrac®) to monitor above-ground activity in wood members, books, boxes and other infested materials.

Most structures had six or more infested monitoring locations, while some had more than a dozen. Distances between monitoring locations and the outside-treated zone ranged from two to 30 feet, encompassing the typical feeding locations of termites in most structures.

All structures were treated once by local pest control firms working under our supervision. A standard 4- to 6-inch trench was dug around the outside foundation wall of each building, into which a 0.06 percent dilution of Termidor or 0.05 percent dilution of Premise was applied at a rate of 4 gallons per 10 linear feet per foot of depth. On basements and crawlspace houses with foundation footings deeper than 1 foot below grade, the dilution was also injected (rodded) into the base of the treated trench to a maximum depth of 2 feet. Deeper rodding was not attempted because practical experience suggests that subterranean termites usually forage within this level. If termites happened to be below this depth, we expected they would eventually encounter the non-repellent soil residues during subsequent foraging nearer the surface. In most cases, porches and concrete slabs adjoining exterior foundation walls were vertical drilled (12-inch spacing) and treated at the aforementioned rate. The reason for this was to provide a continuous zone of treated soil around the entire building. No treating was done on building interiors.

Structures were initially inspected bi-weekly or monthly and periodically thereafter depending on the time of year and level of post-treatment activity at each site. The number of monitoring locations with live termites was recorded, as well as the amount of wood or cardboard consumed.

RECENT RESULTS. Effects on termites infesting several of the exterior-treated structures were discussed in earlier articles (see appended reference citations). Results with Termidor continue to be excellent, as illustrated in the following examples. All three recent sites afforded excellent opportunities to monitor treatment effects on termites foraging within houses.

Unfinished Basement. This small, one-story, brick-sided home in Lexington, Ky., had a concrete block foundation and an unfinished basement. Active mud tubes were present on the basement wall beneath a large, concrete front porch. Termites were feeding on wooden shelves affixed to the basement wall and within a set of old encyclopedias. Two above-ground monitoring stations provisioned with cardboard were established over active mud tubes during November 2000. Both stations remained heavily infested throughout the winter, until treatment the following March. Termites within the encyclopedias were left undisturbed to serve as another monitored location and monthly acoustic emission readings were taken at nine active locations along a 15-foot section of rim joist, above the foundation wall.

On March 23, 2001, the house was trenched and rodded around the outside foundation with Termidor. Perimeter dimensions were 130 linear feet and 114 gallons were applied to a soil depth of about 2 feet. No treatment was performed inside the basement and the only area of drilling was where the front porch slab joined the foundation wall. One month after application, the two basement monitoring stations that had been very active each month since the previous November, were filled with dead, decaying termites and fly maggots. Dead termites were also present in the encyclopedias and thousands were found beneath a stack of books on the wooden shelf. No further activity was detected in monitoring stations or elsewhere within the basement, during 2001-02.

Log House. Another interesting building, perimeter-treated with Termidor, was a restored log house in New Castle, Ky., originally built in 1790. The historic structure had a chronic termite problem and some log sections were heavily infested. The building had been treated the previous year with about 100 gallons of a pyrethroid termiticide, but the infestation persisted due, in part, to difficult construction. The yellow poplar log walls were built over a 2 foot-thick rubble stone foundation and beneath most of the building was an inaccessible crawlspace with little clearance between soil and subfloor. Six very active, above-ground monitoring stations provisioned with cardboard were established on perimeter walls over active mud tubes. Five of the stations were located on the interior and one was affixed to an exterior log surface.

The house was trenched and rodded around the exterior with Termidor on August 2, 2001. Perimeter dimensions were 105 linear feet and 95 gallons were applied. Along the front of the house was an adjoining concrete sidewalk and elevated stoop that were drilled and treated by sub-slab injection. Within a few weeks after treatment, large numbers of dead, rotting termites (accompanied by a putrid odor) were evident in half of the monitored locations. Dead termites and numerous phorid fly larvae, pupae and adults were present in most stations during subsequent inspections and accumulations of dead termites were also found on flooring and other surfaces. Nonetheless, some stations continued to contain live termites throughout the winter until activity ceased the following spring. No termites were detected during the remainder of 2002. In this instance, the extended activity following treatment may have resulted from termites temporarily being isolated above ground, due to the previous application of a repellent pyrethroid termiticide and the high moisture levels present in several of the logs.

Crawlspace. This structure may have been our most challenging test to date of the perimeter treatment concept. Located in Lexington, Ky., the house had a hollow block foundation, brick siding and a full crawlspace. Intense swarms occurred over multiple years and virtually the entire crawlspace area was damp, poorly ventilated and had severe termite damage. Thirteen very active mud tubes inside the crawlspace were selected for observation. Eight were located along inside perimeter walls and five were on three different support piers, about 15 feet farther toward the center. On each inspection date, the mud tubes were slightly and delicately notched with a knife along one side to record whether termites were still present. Previous experience with this technique has produced negligible disruption of termites.

The house was trenched and rodded around the exterior with Termidor on May 29, 2002. Perimeter dimensions were 158 linear feet and 140 gallons were applied to a soil depth of about 2 feet. Drilling and sub-slab injection was used to treat along one outer wall with an adjoining concrete driveway and beneath the front stoop to ensure a continuous zone of treated soil around the entire foundation perimeter. When the crawlspace was inspected one month later, all 13 previously active mud tubes, including those on support piers in the center area, were inactive and some had begun to separate from the foundation wall. Closer examination revealed dead termites packed within several of the tube sections. No live termites were found during subsequent inspections the remainder of the year.

FIELD STUDY SUMMARY. Overall, of the 10 structures treated since 1999 with Termidor, 40 of 43 termite-infested monitoring stations within 1 to 12 feet of the exterior treated trench were inactive after one to three months and all were inactive after six months. Cessation of activity was further supported by diminished acoustic emission and Termatrac readings and the absence of termites in formerly active mud tubes and wood debris. In many Termidor-treated structures (7 of 10), there also was an abundance of dead termites in monitoring stations, mud tubes and previously infested materials. These results are remarkable, considering the high initial infestation levels and that more than half of the monitored locations were on building interiors. The findings are especially noteworthy, given that treatment was performed only on the exterior.

Results thus far with Premise are harder to interpret, since only four structures were treated. As reported earlier (see "Thinking Outside the Box," PCT, March 2001 ), Premise generally had a slower and more limited effect on termites within our in-ground monitoring stations. In some below-ground stations, termites remained active for more than two years before declining. More rapid population decreases following Premise perimeter applications have been reported in trials conducted in Florida (Reid 2001).

In our limited number of Premise-treated sites, visible activity associated with structural components (above-ground monitoring stations, acoustic emission counts, swarms, mud tubes on foundation walls) ceased rather quickly. In a two-year study where Premise was applied around the exterior of 56 termite-infested structures — supplemented by limited spot treatments to infested locations on the interior — structural infestations also were controlled in the majority of cases (Reid et al. 2002). Thus, it is quite possible that Premise (and perhaps other non-repellent liquids such as Phantom), can also afford acceptable protection as a perimeter application, especially if combined with interior spot treatments to infested or high-risk areas.

INDUSTRY SURVEY. It is well known that some companies have begun utilizing perimeter-mostly treatments, even though product labels do not currently support such uses. Retreatment rates from these commercial applications are revealing. Data were compiled from three independently owned, reputable pest control firms in Florida, Texas and Indiana/Kentucky that were willing to share their customer retreatment records. All three companies were using Termidor and had completed a large number of perimeter-mostly jobs in the past few years.

Only termite treatments performed in years 2000-01 were included in the analysis. All applications were made to structures currently infested by termites and most were single-family residences of varying construction. All treatments consisted of a thorough exterior application around the entire perimeter of the building, including beneath stoops, patios and other attached slabs. In most cases, the companies also spot-treated active and high-risk areas (e.g., bath traps), on the interior. For each company, the average annual retreatment rate (as a percentage) was calculated by dividing the total number of jobs treated one year into the number of jobs requiring retreatment the following year. (For example, if a company did 100 jobs in 2001 and 10 required retreatment in 2002, the retreat rate would be 10 percent.)

Results of the retreatment survey can be viewed HERE. All three companies experienced exceptionally low retreatment frequencies with a perimeter-mostly Termidor application. The somewhat higher retreatment rate (2.4 percent) for the company operating in Indiana/Kentucky may have been because half of the houses needing to be retreated (four of eight) did not receive initial spot treatments of infested interior areas. The results overall are nonetheless impressive — 3,817 termite jobs and only 25 retreats — for an average retreat-ment rate of less than 1 percent. That’s pretty amazing, considering that most of the jobs were done in areas of the country with heavy termite pressure — and encouraging, relative to the double-digit rates often experienced with conventional whole-house treatments during the 1990s.

WHY IT WORKS. Despite being controversial, there are reasons why exterior perimeter applications of some non-repellent liquid termiticides (and baits) are effective. Although subterranean termites may appear in the center of buildings, most infestations are associated with perimeter walls and adjoining areas. In the case of one nationwide pest control firm (Orkin), about 90 percent of termite damage claims are associated with perimeter walls (J.P. Hardy, personal communication). One reason for this is that the perimeter is where many vulnerable termite entry points, such as exterior siding, dirt-filled porches, expansion joints and cracks and voids in foundations are located.

Although termites also gain entry through more interior-located openings in concrete slabs (e.g., settlement cracks, utility penetrations), they are commonly following cracks, pipes, edges and other structural guidelines with foraging tunnel connections to the outside perimeter. If termites feeding within buildings did not have foraging connections to exterior soil areas, how would in-ground baiting systems that are primarily installed adjacent to outer foundation walls control termites?

Another reason that termites commonly infest perimeter walls is their preference for moist environments. Perimeter wall areas exposed to rainfall and irrigation usually tend to be moister than locations further toward the center (Lstiburek and Carmody 1994; J. Lstiburek, Building Science Corp., personal communication). Because termites readily tunnel into soil treated with non-repellent termiticides, the temporary zone of moist soil resulting from perimeter application may even serve to "attract" termites, especially during dry weather. Mulch beds, foundation plantings and other landscape features also make building perimeters more susceptible to termites and seemingly the most crucial area for non-repellent treatments.

The likelihood that termites will encounter a non-repellent zone of perimeter-treated soil is further enhanced by their foraging pattern. Studies suggest that subterranean termites construct branching tunnels and utilize a continuous and radiating search pattern while foraging for resources (Hedlund and Henderson 1999, Grace and Su 2001). The extensive network of underground foraging tunnels results in an area being efficiently searched — and is central to the belief that bait stations installed at intervals around a building will eventually be discovered. Termites seemingly would have an even greater probability of encountering a thorough, uninterrupted zone of non-repellent treated soil around the entire foundation of a building.

That said — there is no hard and fast rule for how quickly termites will succumb to an exterior-mostly treatment. Although infestations commonly were eliminated from our Termidor-treated structures in as little as one to three months, the timetable may vary from structure to structure, and product to product. Much as with baits, factors such as time of year, termite species, foraging intensity and proximity to the treated zone may also affect how long before "good things begin to happen."

TREATMENT CONSIDERATIONS. Results to date suggest that an exterior-mostly, perimeter application of Termidor and perhaps Premise or similar non-repellent termiticides, should eliminate termites in most structures. Dogmatic, building-wide drilling and treatment of foundation walls, interior perimeter expansion joints and other non-infested, indoor locations seems unnecessary, especially with products that eliminate termites well beyond the site of application. As a consequence, difficult construction features (e.g., sub-slab ducts and drainage systems, plenums, wood and tile floors, inaccessible crawlspaces, foam insulation/stucco below grade) may become more manageable, as they have become with perimeter-installed bait systems.

Research and practical experience suggests that deep-rodding of foundations and routine drilling of basement floors may also be unnecessary with most non-repellent products. Although termite tunnels can extend deeply into soil, most foraging occurs in the upper few feet since this is where most of the oxygen and food resources, such as plant roots, are located. Populations of termites tunneling deeply around foundations should eventually encounter non-repellent termiticide residues nearer the soil surface. While all liquid termiticide labels currently specify a 4-foot minimum depth when treating along deep foundations, a 2-foot depth might be worthy of consideration and consistent with the widespread desire for less pesticide.

If perimeter liquid treatments are used by the industry, it still may be prudent to selectively spot-treat infested or high-risk interior areas, as is often done with exterior bait applications. (This is why we prefer the term perimeter "mostly" application, rather than perimeter "only.") Supplemental interior treatments using baits, sprays, etc., would also be required in those relatively rare cases where an aerial infestation is present with no soil connection.

A thorough liquid application around the entire outside foundation wall of the building — including beneath adjoining porches, patios, wooden decks, etc. — should enhance the chances of termites encountering treated soil. Partial treatments applied only along infested sections of wall or rodding in lieu of trenching, presumably would be less reliable and may not protect against hidden populations of termites foraging in other areas. Additional treated zones may be warranted around all sides of dirt-filled porches, termite-infested stumps, landscape timbers and elsewhere on the property where termites may be present and where future label directions allow.

REGULATORY CONCERNS. A priority issue with perimeter-mostly applications is their legality. None of the current termiticides are labeled for such uses and the acceptability of such treatments varies by state. In some cases (e.g., Georgia), regulatory officials have gone so far as to issue consumer advisories, warning the public that so-called "trench and treat" applications are not approved and may be ineffective (see PCT magazine, April 2002, page 27). Manufacturers are in the process of seeking state and federal approvals, but as is often the case with label revisions (especially in regard to termites) the wheels of change turn slowly. In the meantime, companies are on their own as to how such treatments should be performed.

What supporting data will be required to modify existing labels… and what degree of effectiveness will be expected? Regulatory bodies are presumably wrestling with such questions. Whatever the standard, hopefully decision-makers will keep in mind that many post-chlordane termiticides have produced double-digit retreatment rates when used in the conventional labeled manner. Experienced applicators recognize that no termite tool works 100 percent of the time. There will be failures with perimeter-mostly liquid applications, just as there have been with baits and traditional treatments. Until such label amendments are granted, no state to our knowledge has the regulatory authority to require that a homeowner have their floors drilled, carpets pulled, etc., provided they sign a waiver acknowledging that all label or state standards are not being fulfilled.

INDUSTRY CONCERNS. Legitimate and important concerns about perimeter treatments have also been raised by pest control companies. One of the biggest is the effect they may have on pricing. Some have even suggested that the approach will cause prices to plummet to levels that will ruin the industry. There is little doubt that such treatments can be offered at a lower cost to consumers, since the amount of labor and chemical required will be less. While the prospect of a reduced cost termite job may be disturbing, low-ball pricing is nothing new to this industry. On the other hand, it’s often been said that the bigger profits in termite work are made on renewals. At a somewhat more affordable initial price, it’s likely that many more property owners would want termite protection for their home, even if it were not currently infested. As a result, the renewal base of companies could increase substantially.

Innovative firms will find additional ways to maintain prices by offering comprehensive and appealing service agreements, perhaps involving joint termite and pest control contracts. Other companies may seek to build value by offering more frequent and thorough inspections or by installing monitoring or baiting systems in conjunction with the perimeter treated zone. (The incremental benefit of such installations in regard to protection of property, however, has yet to be determined.)

Another important question that’s been asked is how long such treatments will remain effective. Clearly, soil termiticide residues along exposed outer foundation walls tend to degrade faster than residues under slabs or within crawlspaces. Although not entirely the same as degradation rates around buildings, ground board test data from the USDA Forest Service suggest that some non-repellents in exposed soil areas (such as trenches), may lose their effectiveness in less than five years, whereas others may persist longer (Wagner et al. 2002).

On the other hand, stopping termites from the outset probably has additional "residual" benefits. Once the original points of entry are denied and the above-ground infestation is eliminated, the rest of the termite population may not return and re-infest for years, even if lethal residues are no longer present. Infestations eliminated from our test structures, including the first one treated in the summer of 1999, have not reappeared. Nonetheless, it still may be prudent to have a label provision allowing retreatment after a period of years, if deemed necessary by the company accountable for the contract.

ENVIRONMENTAL CONSIDERATIONS. An important objective of urban pest management is to reduce pesticide loadings which are unneeded. Perimeter-mostly applications utilize about 40 to 50 percent less termiticide than traditional barrier-type treatments. Potential indoor exposure is dramatically reduced, both for occupants and applicators. Provided such treatments are effective, why should companies be required to dogmatically drill walls and floors, cut tile, move carpet, drag pesticide-laden hoses through homes and pump excessive amounts of pesticide into places where people live? Such treatments are more intrusive, costly and risky to all concerned.

In some circles, liquid applications of any kind are viewed as more hazardous than other approaches, such as baits, physical barriers, etc. Perceptions aside, the mammalian toxicity and hazard of the newer liquid termiticides are generally lower compared to products of the past. Most formulations have caution signal words and negligible volatility. As true of other pest control procedures, customers are generally less concerned about the application of termite control chemicals around the outside of their homes, relative to indoors (Potter and Bessin 2000). Nonetheless, property owners should be educated that there’s a big difference between a targeted termite treatment and a broadcasted lawn care application. (The 6-inch strip of soil adjoining the foundation of a building is not exactly what most would consider a play area or nature preserve.) Once the treated soil has dried, the residues are virtually nondislodgeable and immobile unless the soil is physically moved. Hazards associated with tank spills and mixing can be reduced by using in-line injection systems.

CLOSING THOUGHTS. The intent of this article was to offer a perspective on the growing debate about perimeter treatments. Considering the impact they may eventually have on the industry, such debate is healthy and needed. The bottom line is that there are lots of effective ways to control termites today and each company must choose the approach that is best for themselves and their customers. Perimeter-targeted liquid applications seemingly afford aesthetic, economic and operational benefits that some companies in the future may wish to consider.

All photos are courtesy of M.F. Potter

Dr. Michael Potter is a professor and urban extension entomologist at the University of Kentucky. Anne Hillery is a research scientist at the same institution. Funding for this study was provided by the Kentucky Office of the Attorney General.