Setting Action Thresholds

Actions thresholds are one of the most important, but difficult to implement, aspects of IPM. In simplest form, action thresholds are rules that help the pest control technician know when a particular problem is serious enough to warrant control. For example, a teacher reports a ground beetle to the school office. The teacher doesn’t know whether the beetle poses a problem but is concerned because of its size and appearance. The technician refers to the school’s pest management notebook and determines that the beetle is not a health threat and that thresholds for treatment occur when more than 20 beetles are present in the building.

Action thresholds in a school provide guidelines about when pest levels are serious enough to justify the filing of a work order or complaint. As an example, an IPM coordinator receives numerous complaints from teachers at a middle school about ants. An ant baiting program has recently begun; however, it will take two to three weeks to see results. Frequent call-backs from the school take staff time from other projects; therefore, the coordinator asks teachers to observe a threshold of ten or more ants in a classroom before filing a complaint or work order request.

Action thresholds come from various sources. Specific action thresholds may be suggested by a contractor, by school pest control staff, by consultants, or by committee. You may find thresholds for some pests published in research or extension publications, like this one. Schools can “borrow” action threshold numbers from other schools that have IPM programs already in operation. Borrowed action thresholds can be used as a reasonable starting point, and then modified to suit the conditions at a particular site.

Many action thresholds must be developed from scratch. After determining which pests to include, and which locations need separate action thresholds, schools should decide what pest levels can be tolerated by staff, visitors, and regulatory agencies. These tolerance levels then become your starting point for action thresholds, also known as nominal thresholds.

Two or more thresholds may be needed per pest. This occurs when different control actions are needed for different pest infestation levels. For example, if a technician finds one cockroach in a storage room a few cockroach bait stations may be a sufficient response. But if, say, 30 cockroaches are found, the threshold might require the storeroom to be extensively cleaned, treated with additional insecticides and all cracks and crevices carefully caulked. Such complex thresholds may be referred to as compound or multi-level thresholds.

Schools need action thresholds tailored to their unique staff and facilities. A threshold that works at one school with historically high insect problems may be viewed as too high by staff in a new school building with relatively few pest problems. Although thresholds are best set by a coordinator with high standards for pest management, occasionally it may be necessary to tighten standards for a demanding principal or PTA. On the other hand, some schools may be willing to put up with, say, more weeds in a school yard because of parent or staff concerns about herbicide spraying.

School districts should review their action thresholds regularly, preferably every year. Action thresholds may need to be tweaked, particularly in the first year or two of an IPM program. For example, suppose you request that teachers not file a work order unless they see ten or more flies per classroom. Yet teachers persist in filing work orders when only three or more flies enter their rooms. Your threshold of ten flies per classroom may be unrealistic, based on your teachers’ tolerances.

Listed below are some suggested action thresholds for some common pests and school sites. The thresholds presented here are guidelines for the numbers of pests needed to justify a teacher or staff member submitting a work order or call for service. Similarly, the thresholds might represent the level of pest activity for a technician to attempt to apply a control measure—either chemical or non-chemical.
The list is not complete, and the thresholds, while reasonable, are offered as examples only. Action thresholds at a particular school could be very different, depending on conditions of the school, pest tolerance levels, and other variable factors.


Ants (common sweet feeding)
Classrooms and other public areas: 10 ants/room; infirmary: three ants/room; kitchen: five ants/room; maintenance and storage areas: five ants/100 square feet in two successive monitoring periods; outside grounds: treat nests around building perimeters, as they appear. No treatment necessary in landscapes.

Ants (carpenter)
Classrooms, public areas, maintenance areas: 10 ants/room; infirmary: five ant/room; kitchen: five ants/room; immediate action if ant colony suspected inside or within 25 feet of any building.

Ants (fire ants)
Playgrounds, high maintenance landscapes, athletic fields: report and treat mounds as they appear. In fire ant-prone areas, fire ants may be treated with broadcast baits early in the season to prevent later infestations. Outdoor low maintenance landscapes: one mound/ 1000 ft2. Indoors: 10 ants per classroom.

Classroom, gym or interior of building: One bat found on floor or inside structure
Building Envelop (artificial roosts): Seeing bat droppings, sounds, or evidence of a bat colony inside building.

Bees (honey)
Classrooms, infirmary, kitchen and public areas: two bees; maintenance areas: three bees; treat any colonies in buildings as detected. Outdoors: no action unless children are threatened.

Bees (bumble)
Classrooms, indoor areas: kill individuals as they appear (bumble bees are rare, accidental visitors indoors); Outdoor areas: one suspected nest site (Treatment of bumble bees not needed for foraging bees on flowers).

Bees (carpenter)
Classrooms, indoor areas: kill individuals as they appear (carpenter bees are rare, accidental visitors indoors); Outdoor and outdoor building perimeters: maintenance areas: one suspected nesting site (treatment of carpenter bees not needed for foraging bees on flowers).

Cockroaches (German)
Indoors, most sites: two cockroaches observed per room, or one roach per hot table or box from supplier. Infirmary: one cockroach per room. Outdoors: not applicable.

Cockroaches (American, brown-banded, oriental, smoky brown)
Indoors: two cockroaches. Outdoors: five cockroaches per site.

Classrooms and other public areas: five to ten crickets/room; infirmary: three to five crickets/room; kitchen: three to five crickets/room; maintenance areas: ten to twenty crickets/room; outside grounds: no action unless perceived as causing problems.

Grain and flour pests
Found in food for human consumption: one/package or container; pet food: five if escaping from packaging; if found in pheromone traps: two of any one species (total of all traps).

House flies
Classrooms and other public areas: three flies/room; infirmary: two flies/room; kitchen: one fly/room; maintenance areas five flies/room; outside grounds: five flies around any one trash can or ten flies around a dumpster.

Lice (head or body)
Refer any students suspected of being infested to nurse immediately. This is a medical condition, not a pest control problem.

Indoors: any mouse sighting or fresh evidence of mice (e.g., new mouse droppings, tracks, etc.); outdoors: any noticeable burrows or activity under or around school buildings.

Roof ledges: 10/building for three consecutive inspections; public area or roof: whenever droppings accumulate more than one inch or nests obstruct gutters or equipment.

Poison Ivy
Student activity areas: one plant; wooded areas: no control recommended unless near path or student activity area.

Indoors: any rat sighting or fresh evidence of rats (e.g., new droppings, tracks, etc.); outdoors: any active burrows or activity under or within 100 feet of school buildings.

Library and wherever books, paper, files are stored: three/room; other indoor areas: five/room.

For black widow or brown recluse spiders, one spider per location. All other (non-venomous) spiders – Classrooms: three spiders/room; infirmary: three spider/room; kitchen/cafeteria: five or more spiders/room; hallways: five spiders/hallway; maintenance and unoccupied areas: ten spiders/room; outdoors: no treatment recommended.

Indoors: Report any termite swarmers, or other evidence of live termites or previously undetected damage in indoor areas. Outdoors: Report any evidence of mud tubes climbing school buildings.

Outdoor student activity areas: 3 ticks, any species; outdoor wooded and other areas of low student activity: keep grass and weeds trimmed; if any blacklegged ticks found, treat wood edges; for other species, take action if moderate to heavy populations.

Outdoor high maintenance landscapes: 20% weed cover in any 100 square foot area; or whenever perceived as competing with ornamental plants. Other outdoor sites: whenever aesthetically displeasing, potentially damaging to buildings or block visibility needed for security.

Wasps (yellowjacket wasps/hornets)
Classrooms, indoor areas: kill individuals as they appear (yellowjacket wasps are rare, accidental visitors indoors); Outdoor and outdoor building perimeters: maintenance areas: one suspected nesting site (treatment of yellowjacket wasps not needed on flowers). Ten per ten minutes at trash cans or dumpsters; Playgrounds, outdoor lunch areas: report any incidents where children are threatened or stung.

Wasps (paper)
Classrooms, indoor areas: kill individuals as they appear (paper wasps are rare, accidental visitors indoors); Outdoor and outdoor building perimeters: Report any wasp nests within 20 feet of human activity.


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