[Rodent Control] Commercial Exterior Rodent Baiting Programs, Part III: Time for Evaluation

As discussed in Parts I and II of this series in PCT magazine (August and October 2005), various large-scale food-handling establishments employ up to hundreds of exterior bait stations within a "three lines of defense" model to protect their establishments against potentially invading rodents. But over the past few years, some clients have been inquiring as to whether or not this model is appropriate for all exterior environments, considering there are large-scale variations in rodent species, rodent pressures, non-target animals, and a range of mammal and bird predators that feed on rodents killed by exterior baits.

Additionally, the cost-benefit aspects of these programs are being considered. It’s a fair argument, for example, that if a large warehouse utilizing 150 exterior bait stations receives activity on roughly the same 40 stations each month, then are not the remaining 110 stations and all the time and materials to service them essentially overkill and a potential waste of resources? When calculated over the course of a year, the monies saved not servicing these stations are indeed significant, especially if this warehouse is located in an area containing low natural rodent pressure.

And finally, as emphasized in Part II, some highly notable companies in the food and pharmaceutical industry desire to have a "green image" associated with their company and their products. This is especially true relative to their use of pesticides, including rodenticides.

But what alternatives to the conventional three lines of defense are available? Is it possible to provide maximum product safety for food-handling establishments, while also being environmentally sensitive and maximizing cost effectiveness? I think so. In fact, with exterior rodent control programs, maximizing the cost-effectiveness of some programs often concurrently results in minimizing the environmental impact of these programs as well.

ALTERNATIVE PROGRAMS. For facilities wanting alternatives to exterior rodent baiting for either green programs or for fine tuning cost-effectiveness, there are four practical and effective options:

1. Exterior mouse snap trap stations. Mouse snap traps (two to three traps) can be installed into conventional bait stations (e.g., Protecta, Aegis, Multiplex, JT Eaton, etc.), which renders the stations "trap stations." (See Figure 2 on page 46.) Traps with plastic bases and kill-bars are best suited to withstand exterior conditions. The traps can be located within the bait-holding compartments and baited using an odorous food item such as peanut oil, chocolate syrup, meat grease, etc. Avoid using food items that can be carried off by exterior insects, such as ants. If rats are periodical visitors to the site, the mouse trap stations will need to be supplemented with conventional bait stations and/or monitoring stations.

2. Monitor stations. Non-toxic bait monitoring stations can alert us to the presence of rodents in an area (see Figure 1 on page 44). As a sole approach for large-scale rodent management programs, they have limited practical utility. This is because the mouse is the most common rodent pest foraging about along the exterior wall areas and it must be stopped. But, monitor stations can be used in combinations efforts for the reasons discussed in number 3 below.

3. Combination of trap stations and monitor stations. Combinations of exterior mouse trap stations with a few strategically installed monitoring bait stations (with Detex blocks perhaps) provides the most useful of any of the four options. Exterior mouse snap trapping programs as a sole approach are not well suited for those buildings that also might be subjected to periodical rat pressure. Thus, exterior mouse trapping stations can be supplemented with monitoring bait stations. The primary goal of monitoring bait stations is to provide proactive monitoring for any rats that might immigrate towards any building exteriors.

In general, rat infestations are significantly less common than mice for most areas of the country. Moreover, rat infestations are readily identifiable and attributed to a local environmental situation. For facilities subject to ongoing rat pressures, conventional baiting programs are necessary.

4. Exterior multiple-catch trap stations. Multiple catch mouse traps (e.g., Ketch-All, Tin Cat, 24/7, Pro-Ketch, Repeater, Mouse Master, etc.) also can be used for exterior mouse control programs. Exterior MCTs are best if installed within protective covers or large bait boxes (i.e., MCT stations).

Additionally, multiple catch traps must be kept clean and in good working order. It is not as easy to clean multiple catch traps of dead, decaying carcasses than it is with snap trap stations. Thus, for facilities under heavy mouse pressure, the repeating curiosity traps are not cost effective due to the amount of servicing time associated with emptying and cleaning successful traps. In fact, facilities subject to heavy rodent pressure are better suited for conventional rodenticide baits or a combination of bait stations and snap trap stations.

QUANTITY & LOCATION SUGGESTIONS. In conventional exterior rodent control programs, rodenticide bait stations are typically established around the perimeter walls of a building at spacings ranging from 25, 50 or 100 feet (8, 15 or 30 m) depending on the rodent pressure, the wishes of a specific client or as directed by the guidelines of an independent inspection agency (AIB, Silliker Labs, NFP, etc.). Again, this surround-the-perimeter concept is based on providing a uniform protective barrier to intercept any rodents approaching the exterior from any point and traveling along walls to hopefully encounter a trap or bait station.

This concept originated from models designed to protect grain silo storage operations. Grain storage buildings tend to have exterior spillage, grain odor emanating out from all sides, and are often less structurally tight as are stores, warehouses and food plants. Thus, it is questionable to have a bait station placed every 50 feet all around a large warehouse, plant or store, if the only rodent activity is consistently originating from say, the southwest corner of the building involving only a couple of bait stations. Moreover, why should a 600-foot long exterior solid wall, with no doors and no penetrations through the wall receive 12, or even six, bait stations? (See Figure 3 on page 50.) In alternative programs, there is no such "yardstick measurement" placing of stations. The locations of the stations are based upon those areas of a building where rodents are likely to be attracted to, or from the obvious building locations where they may attempt to enter.

HISTORY SHOULD DICTATE PROGRAM. The basis for alternative exterior rodent control programs is to simply consider the history of the rodent problems inside and outside the facility. Has it been low, moderate or heavy? As a baseline starting point for facilities that experience low, or only occasional, mouse activity, as few as 10 trap stations and two monitoring stations can suffice for a building the size of a large rectangular-shaped retail store (i.e., short and long walls).

As seen in Figure 4 at www.pctonline.com, two trap stations can flank the building’s main delivery doors, and two flanking the main entrance doors. Two additional stations can be installed along the long walls positioned within approximately 25 feet/8 m from each of the wall’s connections to the short walls. For each of the short walls, one trap station can be placed at the middle of the wall. These eight trap stations can then be supplemented with two monitoring stations for rats installed flanking both sides (within about 10 feet) of any refuse container serving the store (e.g., compactor, Dumpster). The refuse area often serves as an area odor attractant for flying insects, birds, and rodents, and thus is a logical location for such monitoring stations. But, the location of these stations is discretionary and the on-site professional should make the call.

The configurations of how rodent control stations can be installed around a building should be dictated by the pressure. Over the course of time, a pest professional’s observations and experience together with the activity data can dictate if more or less stations are necessary. Perhaps additional stations will need to be installed along the one wall where there is more activity and where the interior mouse traps are showing higher weekly captures.

THE PROPERTY LINE. Should the property line/fence row areas receive bait/trap stations in alternative programs? If the building is close to the property line, and there are obvious conditions conducive to rodent populations (thick vegetation, clutter, suspect neighboring properties, waterway, railway embankments), these areas can be monitored with snap trap stations, or possibly non-toxic bait stations to monitor for rats.

If, however, the perimeter walls opposite those property lines or fence rows show very little or no rodent activity and/or the property line is a considerable distance (e.g., greater than 25 yards), than there is probably little justification for any pesticidal stations. But, the servicing pest professional should occasionally inspect along property line areas to note any developing issues.

FACILITIES WITH RAT PRESSURE. For facilities where rats (either species) are established in the area, and periodically interact with the premises, more conventional property line and perimeter wall baiting programs of 50 or 100 foot spacings are recommended. These stations can be serviced on a monthly or semi-monthly (i.e., bi-weekly) basis depending on the rat pressure on the particular store or distribution center.

If rat pressure is only occasional, these facilities can be monitored for any immigrating rats employing the Detex monitoring programs as discussed previously. Should rat activity occur, the Detex baits can be switched out with regular rodenticide baits.

It is important to note that unlike mouse control programs, rat trap stations have two significant limitations for providing rat control around a building, one of which is an environmental drawback. First, rat traps can be triggered by mice or other small foraging mammals, which then eliminates any type of rat protection being available to the rats. Second, rat traps will kill birds and may seriously harm, or even kill, some inquisitive non-target wildlife interacting with rat trap stations (e.g., tree squirrels, ground squirrels, chipmunks, raccoons). With ordinary mouse traps, this will not occur (although small birds may be killed by mouse traps). However, for those buildings located in city areas where rats are the predominant exterior rodent pest, then, rat bait or trap stations may be the most appropriate exterior option.

Advantages of Exterior Rodent Trapping Programs. Several advantages exist for substituting trapping programs over pesticidal baiting programs, including:

1. Trapping programs dramatically reduce the overall amount of pesticide used in a company’s pest management program, because there are no pesticidal baits to discard and replace.

2. From a food safety advantage, exterior traps can stop mice prior to them entering the building. When baits are employed, rodents that have been poisoned by the bait may live for another three to 12 days following bait ingestion. During this delayed death period, rodents still may enter the building and will need to be captured within one of the interior mouse traps to prevent them from dying in inaccessible areas or equipment, contaminating product, or hiding in outgoing product and causing problems on the receiving end. Such mice cause significant inconveniences for the food industry. Simply put, with exterior trapping stations, the majority of rodents foraging about food-handling facility building exteriors are "accounted for."

3. When exterior traps are employed instead of baits, poisoned rodents are not available to non-target species (e.g. hawks, owls, foxes, cats, dogs, and other predaceous wildlife). These predatory animals are not uncommon around many large-scale facilities (especially for some large-scale distribution centers now located several miles outside of cities and towns).

4. From a cost-savings aspect, unvisited trap stations do not require any replacement of a trap. Compare this against the mandatory need to switch out pesticidal baits on at least a monthly basis — even for those buildings that do not have any rodent pressure. This can be considerable savings for a client when accumulated on the large-scale level for those facilities with low rodent pressure.

SUMMARY. Exterior baiting programs should be conducted in the same manner as any component of urban pest management involving possible pesticide applications and the specifics of such applications. For pest professionals offering IPM services to any aspect of the food industry, exterior rodent control programs and possible rodenticide applications requires being adept at situation analysis; that is, considering the local environments, inspection results, bait station data review and the history of any current and previous rodent activity at the property.

For facilities subject to ongoing high rodent activity, their property lines and building perimeters both require maximal rodent protection by either the use of baits or trap stations installed in the conventional "yardstick measurement model."

Similarly, facilities with low rodent pressures and wishing to be more environmentally conscious, or perhaps more cost conscious with their pest management program, are ideal candidates for alternative programs. The number and placement of rodent control devices can be limited and strategically placed without jeopardizing food safety.

Author’s note: References for this three-part series were included in Parts I and II.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829.

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Click here to view a simple schematic for an alternative exterior rodent control program for a facility with low rodent pressure.

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SERVICE FREQUENCY CONSIDERATIONS

Unlike bait stations, which are usually serviced at least monthly, trapping stations must be checked weekly for those buildings that have moderate or significant exterior mouse activity. For facilities with minimal or virtually no rodent activity, the trap stations can be serviced on a bi-weekly basis (i.e., every other week).

These servicing frequencies are especially important during the warm weather months. Obviously, if traps are not inspected and emptied on a timely basis during the summer, decaying carcasses will attract filth flies and other pests to the station where they may feed on the carcasses. These same pests may leave the stations and enter the building.