[Vertebrate Pests] Rodent Baits In Schools

Well, as the saying goes, unless you’ve been living in a cave somewhere for the past 13 years, you know there is a strong "IPM in schools" effort in the United States. For the most part, this effort means that the applications of pesticides such as insecticides, herbicides and rodenticides in and around schools are carefully controlled. In fact, within most school districts practicing IPM programs, pesticides are considered "last options" for correcting pest infestations.

Certainly, every pest professional knows the old procedure of spraying baseboards as a "preventive measure" to keep ants, spiders, cockroaches and other insect pests out of classrooms and kitchens has no place in school IPM programs (or in most other environments as well).

The public has spoken loud and clear on this: school children (and staff) should not be exposed to pesticide applications (e.g., liquid sprays, aerosols, dusts, etc.). Whether you agree or not, it is now a moot point whether or not small amounts of the more advanced pesticide formulations applied carefully according to label directions pose any significant health threat relative to the various other chemicals used in cleaning and maintaining the school.

The general rule of pesticide applications for school IPM programs can be summarized as this: if there are no pests present, then there is no need for any pesticidal treatments.

This premise seems reasonable when it comes to most insecticide and herbicide applications. But what about rodenticide applications? Well, there are some subtle considerations that render these pesticides different from insecticide and herbicide applications. In fact, not using baits as a preventive means to control mice may in fact cause some unforeseen dangers to school students and staff. Let’s examine why this is so.

ONCE-A-MONTH SERVICE. Many school districts do not budget enough money to provide for pest control service for more than once a month. In fact, the majority tries to keep the pest control service contract bid as low as possible. Thus, it is common for a school to not only be serviced once a month, but in additional efforts to keep the bids low, only certain parts of the schools are designated for service (e.g., kitchens, lavatories and any areas calling in pest sightings).

Once-a-month schedules can work for schools with low rodent pest pressure. But in other areas and situations, such as for schools surrounded by crop fields, undeveloped acreage and/or woods, significant numbers of mice may disperse to the school each autumn when crops are harvested or temperatures drop. Inner-city schools on other hand may sustain constant mouse activity due to chronic populations from nearby buildings in the area.

Rodents entering and then occupying buildings are often secretive about it. They are not like ants, cockroaches, flies or wasps, all of which typically are noticed fairly quickly. Mice, however, are mostly active at night when no one is in the school and may be active in ceilings, closets, furniture voids and other out-of-sight areas within a school for days, weeks or even months before anyone becomes aware of their presence. With the high reproductive potential of the house mouse, these situations pose some dilemmas relative to using only a non-pesticidal approach.

It’s not that non-pesticidal approaches (i.e., traps) won’t work. They can. But trapping programs in schools serviced only once a month will require a school staff member helping to check and service at least certain traps during the interim between service visits. For traps that are installed in out-of-sight and non-threatening areas, (e.g., basements, crawl spaces, some ceiling spaces, etc.), a trapped mouse is not likely to be of any odor concern or health threat. But in more sensitive areas of the school, such as kitchens, food storerooms, classrooms and offices, several weeks is too long for a mouse to remain in a trap unserviced.

So how much of a pesticidal risk is there to children and staff if rodenticidal baits are installed in prescribed methods in schools on a preventive basis?

To answer this, it is helpful to keep in mind that the primary objective of school IPM programs is to prevent children from being exposed to both pesticides and pests. For instance, children should not be exposed to the residual particulate matter from mouse urine and feces. Proteins in mouse urine have been demonstrated to be highly allergenic to some children and mouse feces may contain pathogenic microbes, such as the Lymphocytic choriomeningitus virus (LCMV).

This fact should not be overlooked, because rodenticide baits are often lumped into "the pesticide risk" group (i.e., the same as insecticidal sprays, aerosols, etc.), when school IPM programs are designed to simply minimize the use of "pesticides." The use of rodenticides is somewhat unique relative to preventive rodent control and the formulation in which rodenticides can be administered.

Consequently, we should be careful to compare risks. Can rodent baits be used inside schools and child-care facilities as a preventive, ongoing program without compromising safety to the students? In other words, can such a program be totally compatible with the intent and spirit of school IPM programs? Certainly. But some considerations are important.

RECOMMENDATIONS. The following are a few suggestions and guidelines for the preventative use of rodent baits in schools where mouse pressure is constant and budgets prevent more then once-a-month service.

1. Only licensed and experienced pest management professionals should apply rodenticide baits in schools. This is not a job for the school custodian or the maintenance supervisor, using a "homeowner" approach of placing out a some "green poison pellets" underneath the sink, or installing a box or placepack of an over-the-counter mouse bait behind the refrigerator in the teachers’ lounge. Although such applications seem simple and are done by millions of homeowners, things can, and have, gone wrong. It is the professional pesticide applicator that has the training and the experience to bait skillfully in sensitive environments, such as child-care facilities.

2. Bait blocks secured inside tamper-resistant bait stations are the only acceptable rodenticide formulation and application for schools.

3. Bait stations should be installed only into inaccessible areas. This practice provides for maximum safety and effectiveness. Rarely (if ever) should there be a circumstance when a bait station would need to be placed in an area where a student or staff member would encounter or even see the station. One of the great tenets of effective rodent baiting is to deliver the bait into the high activity zones of the rodents. It is far less effective to simply place the bait in those areas that are easiest for the applicator to find. Doing this assumes the rodents will travel and find applied baits. Although individual rodents may be eliminated in this way, the infesting rodent colonies are for the most part unaffected. In most cases, the high activity areas of rodents are also in areas out-of-sight and out-of-reach for students.

4. All bait stations should be numbered, an informal map maintained of the stations’ locations, and a copy of the station map provided to the appropriate school personnel.

5. Pellet-style and/or packet style baits should never be used for schools as the pellets and packs are prone to being carried off (translocated) by rodents. Such baits could then end up in areas where students might encounter them, or in areas where they might contaminate foods or food surfaces.

CONCLUSION. Despite the appropriateness of rodenticidal baits for these situations, there are those times where baits are not a good fit. As implied previously, schools with low mouse pressure, should use trapping programs. Trapping programs are also a better choice for initial mouse programs dealing with severe infestations. There are three reasons for this. First, with large populations of mice, there is a good chance of poisoned mice appearing or dying in occupied areas; second, if large numbers of mice are all poisoned within the same period, there is the possibility of repulsive carcass odors occurring. And third, if large numbers of mice are poisoned during the fly breeding seasons, a blow fly infestation could occur at the school.

Can accidents occur with rodenticides in schools? Of course. Accidents can happen with any chemical used at a school (cleaning agents, paint fumes, floor stripping compounds, etc.). But if it was my child in an elementary school tightly budgeted and subject to chronic mouse infestations, and I had to measure the risks between the mice or allowing rodenticide baits to be applied by experienced professionals according to label directions installed into out-of-sight areas, I would vote the bait route every single time.

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