How to apply a perimeter pest spray correctly

When a perimeter spray helps, and when it doesn't

A perimeter spray works on insects and spiders that walk in from outside. It does nothing about a nest that is already inside the walls, and extension specialists disagree on how much it helps against several common pests.^[4][3]

• Spiders: Kentucky Extension says a barrier spray around the outside of the building, paying attention to door thresholds, garage and crawl space entrances, foundation vents and the bottom edge of siding, is effective but may need repeating monthly or every other month in warm weather.^[7]
• Carpenter ants: Ohio State says perimeter treatments are used outside the structure to deter ant entry, alongside treating the nest itself.^[8]
• Odorous house ants: Texas A&M says that when many ants show up around the foundation, a residual perimeter treatment may repel foragers and keep them from coming back in.^[6]
• Ants in general: UC IPM says spraying around the foundation won't give permanent control, because it kills only foraging ants, which are a small part of the colony, and the ants soon build back up. Sometimes the barrier traps ants indoors and makes things worse.^[4]
• Fall invaders such as boxelder bugs and lady beetles: Illinois Extension says perimeter sprays can be used, but these insects move around so much that good control is hard. Sealing gaps around the foundation, pipes, wires and chimneys is the main defense.^[3]

What the label controls

Professional bifenthrin labels set the mixing rate for outside surfaces and perimeter treatment, the sites allowed, and restrictions meant to protect water and pollinators.^[1]

Bifenthrin is extremely toxic to fish and aquatic invertebrates and highly toxic to bees exposed to direct treatment or residues on blooming plants.^[1]

Use the amount the label calls for; applying too much increases exposure for people, pets and the environment without better control.^[2]

Pyrethroid labels now specify revised application procedures for outdoor use around homes. In a California study of test house lots, runoff losses were 40 times lower when pyrethroids were applied the revised way those labels now specify.^[16]

Using the bifenthrin label as the example, outdoor sprays around homes must be spot or crack-and-crevice treatments, except for these uses:^[1]

• Soil, lawn, turf and other vegetation.^[1]
• A perimeter band no more than 7 feet wide, measured out from the base of the building, onto pervious ground such as soil, mulch or lawn.^[1]
• Undersides of eaves and soffits, and doors or windows that are permanently sheltered from rain by an overhang, awning or other cover.^[1]
• Around doors, windows and other entry points, in a band no wider than one inch.^[1]
• Walls above driveways, sidewalks and other hard surfaces, up to 2 feet above ground. Walls above soil, lawn or mulch only where that ground doesn't drain into ditches, storm drains, gutters or surface water.^[1]
• Spot treatments may not exceed two square feet. Do not spray flat hard surfaces such as sidewalks, driveways and patios except as a spot or crack-and-crevice treatment.^[1]
• The same label's section on outside surfaces allows foundation walls to be treated up to 3 feet from the ground, and its perimeter directions mention a band of 6 to 10 feet wide and 2 to 3 feet up the foundation. That section also tells you to follow the residential restrictions above, which cap the band at 7 feet.^[1]

Band width, height and how often

Ohio State describes a perimeter spray for carpenter ants as applied against the foundation wall, typically 2 feet up and 3 feet out, plus under the lower edge of siding, around window and door frames and around chimney flashing. A Purdue field study of barrier sprays for ants used the same 2-foot-up, 3-foot-out pattern.^[8][12]

• Measure the product with proper measuring tools, not household utensils. This label allows a 0.02 to 0.06% dilution for outside surfaces and up to 10 gallons of spray per 1,000 square feet, more where plants or landscape materials are dense.^[1]
• How often: the label says to repeat only if there is evidence of renewed insect activity, and not more than once per 7 days.^[1]
• Extension schedules vary: Ohio State says to reapply every four to six weeks in summer or within a week after a heavy rain, and Kentucky says monthly or every other month in warm weather for spiders. Neither overrides the label.^[8][7]
• Use the amount the label calls for and no more; NPIC notes that extra pesticide raises exposure for people, pets and the environment.^[2]
• Make sure the label lists the place you're treating. NPIC notes that using a pesticide in an unlisted location is illegal and unsafe.^[2]

Rain, runoff and water

Runoff from treated homes can carry insecticide into urban streams. UC Riverside researchers measured runoff after homes were sprayed for ants following standard practices: bifenthrin from sprays reached 14.9 micrograms per liter one week after treatment and 2.5 at eight weeks, both high enough to harm sensitive aquatic life. Bifenthrin granules left no detectable bifenthrin in runoff after eight weeks.^[15]

In the California house-lot study, sprays on the driveway, garage door and the walls next to it accounted for 99.75% of measured runoff losses, and most of the loss came with heavy rain rather than lawn sprinklers.^[16]

• Don't let spray enter or run off into storm drains, drainage ditches, gutters or surface water.^[1]
• Don't spray during rain. Avoid spraying when rain is expected before the product has dried (at least 4 hours); rain within 24 hours may still cause runoff.^[1]
• Don't spray when wind is over 15 mph, and don't apply or water the area to the point of runoff.^[1]
• For soil or foliage sprays, stay at least 25 feet from lakes, rivers, permanent streams, marshes and natural ponds, and keep spray away from fish ponds.^[1]
• In the UC Riverside trials, spray-free zones and pin-stream perimeter applications reduced runoff.^[15]
• Non-repellent products are not runoff-free: a fipronil perimeter spray in the same study reached 4.2 micrograms per liter in runoff one week after treatment, also potentially toxic to sensitive aquatic organisms.^[15]
• Because of water quality concerns, California's Department of Pesticide Regulation adopted rules limiting perimeter treatments with pyrethroids.^[4]

Bees and blooming plants

The label's perimeter band covers the soil and vegetation next to the building, so check that strip for flowering plants and weeds before you spray.^[1]

• Bifenthrin is highly toxic to bees exposed to direct spray or to residues on blooming crops or weeds. Don't spray it, or let it drift, onto blooming crops or weeds while bees are visiting.^[1]
• UC IPM says to avoid spraying insecticides on any plant in flower and to keep drift off nearby blooming plants, weeds included.^[11]
• Residues can stay toxic to bees for hours to a week or more, depending on the product.^[11]
• UC IPM also notes that some bees spend the night on plants or in the soil, so a late-day spray does not avoid every bee.^[11]

Repellent vs non-repellent insecticides

Ohio State notes that pyrethroids (names usually ending in "-thrin") have a repellent action. Non-repellent products such as fipronil and imidacloprid don't drive insects away; Kentucky Extension explains that termites tunneling into soil treated with them are killed, where older repellent products only turned them aside.^[10][9]

• Why it matters for ants: Ohio State says repellent pyrethroids can move Pharaoh ant colonies and spread them through a building. In a Purdue lab study, the repellent pyrethroid cypermethrin caused Pharaoh ant colonies to split (budding), while fipronil gave the best control on concrete and mulch.^[10][13]
• Utah State says repellent barrier sprays that cut an odorous house ant trail between outdoors and indoors can leave ants stranded inside and cause new problems there.^[5]
• In the Purdue field study at an apartment complex, all three barrier sprays cut ant numbers. Fipronil was most effective, with 2% of pre-treatment numbers left at 8 weeks; imidacloprid matched it for 4 weeks and the pyrethroid cyfluthrin for 2 weeks.^[12]
• Fipronil also spreads through a colony: in UC Riverside lab work, Argentine ants that touched fipronil-treated sand passed it to nestmates, causing high mortality. The other insecticides tested were not passed on.^[14]
• Ohio State notes that a perimeter treatment for carpenter ants often includes spraying ant trails with a non-repellent product so more foragers are exposed.^[8]

Protecting people and pets

• Keep children, pets and sensitive people out of the area while you apply.^[2]
• Do not apply to pets, and keep people and pets off treated surfaces until dry.^[1]
• Store food, toys, pet bowls and clothing away from the treatment.^[2]
• Wear at least the gloves, goggles and other gear the label lists. NPIC suggests adding more protection to lower your exposure further.^[2]
• Stay out of treated areas for as long as the label directs.^[2]

Common questions

How wide should a perimeter spray band be?

No wider than the label allows. On the bifenthrin label used here the cap is 7 feet from the base of the building, onto soil, mulch or lawn. Ohio State describes a typical band for carpenter ants as about 3 feet out and 2 feet up the foundation.^[1][8]

How often should I spray the perimeter?

Only as often as the label permits. The bifenthrin label says to repeat only when insects come back, and no more than once every 7 days. Extension schedules range from every four to six weeks (Ohio State, carpenter ants) to monthly or every other month (Kentucky, spiders).^[1][8][7]

Will a perimeter spray get rid of ants?

Usually not for good. It kills foraging ants, not the queens and the rest of the colony, and the ants rebuild. UC IPM recommends baits in bait stations as the safer, more effective choice for home ant problems.^[4]

Can I spray the driveway or sidewalk?

Not as a broadcast spray. The label allows only spot or crack-and-crevice treatments on flat hard surfaces, because in a California test, sprays on driveways, garage doors and the walls beside them caused nearly all the measured runoff losses.^[1][16]

Sources

1. U.S. EPA Pesticide Product Label System, “Bifenthrin TC (Bifen I/T) label, EPA Reg. No. 53883-118 (EPA-stamped, September 1, 2026).” www3.epa.gov/pesticides/chem_search/ppls/053883-00118-20260901.pdf (accessed 2026-10-06)
2. National Pesticide Information Center, “Minimizing Pesticide Exposures.” npic.orst.edu/health/minexp.html (accessed 2026-10-06)
3. University of Illinois Extension, “Fall house guests (Sept. 23, 2019).” extension.illinois.edu/news-releases/fall-house-guests (accessed 2026-10-06)
4. University of California Statewide IPM Program, “Pest Notes: Ants, Publication 7411 (October 2012).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnants.pdf (accessed 2026-11-10)
5. Utah State University Extension, “Odorous House Ants (R. Davis and A. Taylor, October 2019).” extension.usu.edu/planthealth/research/odorous-house-ant.pdf (accessed 2026-11-10)
6. Texas A&M AgriLife Urban and Structural Entomology Program, “Odorous House Ant, Tapinoma sessile.” urbanentomology.tamu.edu/urban-pests/ants/odorous-house-ant/ (accessed 2026-11-10)
7. University of Kentucky Entomology, “Eliminating Spiders Around Homes and Buildings (ENTFACT-623).” entomology.mgcafe.uky.edu/ef623 (accessed 2026-11-10)
8. Ohio State University Extension, “Carpenter Ants, HYG-2063 (2017).” ohioline.osu.edu/factsheet/hyg-2063 (accessed 2026-11-10)
9. University of Kentucky Entomology, “ENTFACT-604: Termite Control: Answers for Homeowners (revised March 2026).” entomology.mgcafe.uky.edu/ef604 (accessed 2026-11-10)
10. Ohio State University Extension, “Pharaoh Ant, HYG-2136 (2011).” ohioline.osu.edu/factsheet/hyg-2136 (accessed 2026-11-10)
11. University of California Statewide IPM Program, “Best Management Practices to Protect Bees From Pesticides.” ipm.ucanr.edu/mitigation/protect_bees.html (accessed 2026-11-10)
12. Journal of Economic Entomology, abstract via PubMed, “Impacts of residual insecticide barriers on perimeter-invading ants, with particular reference to the odorous house ant (Scharf, Ratliff and Bennett, J Econ Entomol 2004; PMID 15154488).” pubmed.ncbi.nlm.nih.gov/15154488/ (accessed 2026-11-10)
13. Journal of Economic Entomology, abstract via PubMed, “Efficacy of simulated barrier treatments against laboratory colonies of Pharaoh ant (Buczkowski et al., J Econ Entomol 2005; PMID 15889742).” pubmed.ncbi.nlm.nih.gov/15889742/ (accessed 2026-11-10)
14. Journal of Economic Entomology, abstract via PubMed, “Horizontal transfer of insecticides in laboratory colonies of the Argentine ant (Choe and Rust, J Econ Entomol 2008; PMID 18767753).” pubmed.ncbi.nlm.nih.gov/18767753/ (accessed 2026-11-10)
15. Pest Management Science, abstract via PubMed, “Impact of ant control technologies on insecticide runoff and efficacy (Greenberg et al., Pest Manag Sci 2010; PMID 20730990).” pubmed.ncbi.nlm.nih.gov/20730990/ (accessed 2026-11-10)
16. Environmental Toxicology and Chemistry, abstract via PubMed, “Major transport mechanisms of pyrethroids in residential settings and effects of mitigation measures (Davidson et al., Environ Toxicol Chem 2014; PMID 24105831).” pubmed.ncbi.nlm.nih.gov/24105831/ (accessed 2026-11-10)