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Aerosol Killer Sprays application — Ant & Roach Killer Spray by Black Flag
Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

How to Use Ant & Roach Killer Spray by Black Flag

WorkhorseImiprothrin 0.100%Lambda-cyhalothrin 0.025%
Used correctly, Black Flag Ant & Roach Killer Spray works well for exactly one job: killing the ants and roaches you can see and treating the cracks and harborage they hide in. It's a ready-to-use pyrethroid aerosol (imiprothrin plus lambda-cyhalothrin on the standard unscented SKU — confirm the panel on your can, since Black Flag reformulates by variant) that you aim directly into baseboard gaps, under appliances, and around entry points until the surface is slightly wet — never fogged into the open room. Direct hits knock pests down in seconds to minutes, and the light residual keeps working on treated cracks afterward. What it does NOT do is solve an established infestation: independent testing on this class of pyrethroid contact spray found under 20% mortality against German cockroaches exposed to treated surfaces, because the reproducing population behind the wall is never touched. Never spray it over or near a bait you're using — the residue repels the pests you want carrying bait back to the colony — and if roaches or ants keep returning after a few weeks of correct spot treatment, that's your signal to bait or call a professional.

At a glance

  • Efficacy: Workhorse
  • Best job: Fast, direct-hit knockdown of ants and roaches you can see, plus a light residual on the cracks and harborage you actually spray
  • Format: Ready-to-use (RTU) pressurized aerosol — no mixing. Black Flag sells more than one Ant & Roach SKU (a standard water-based aerosol and a separate 'Dry' formula with a different active/propellant), so confirm the printed active-ingredient panel and EPA Reg. No. on the can in hand before relying on an exact residual claim.
  • Technique: Easy technique
The honest verdict

Does this product actually work?

The verdict on this product
WorkhorseEasy technique
Workhorse

A solid workhorse for direct-hit knockdown and crack treatment — the same honest ceiling as every synthetic-pyrethroid contact aerosol.

Aimed into cracks, baseboards, and harborage rather than the open floor, this is a genuinely fast, reliable knockdown tool for visible ants and roaches — it behaves like every other synthetic-pyrethroid contact aerosol on the market. But the same 2024 University of Kentucky/Auburn research that grades Raid and Hot Shot's contact sprays applies here too: pyrethroid sprays killed under 20% of German cockroaches exposed to treated surfaces, and the colony behind the wall is never touched. Treat it as a spot tool for what you can see, not a cure, and pair it with baiting or professional treatment when sightings persist.

Best for

Killing the ants and roaches you can see and treating the cracks and harborage where they hide.

Skip it for

Ending an established German cockroach infestation or a hidden ant colony — comparable pyrethroid contact sprays kill fewer than 1 in 5 German cockroaches on treated surfaces in controlled testing.

Read the label first

What it is — and what it's really for

The label is the law. Here's the honest read on the format, the one job it does well, and the job people wrongly buy it for.

Format
Ready-to-use (RTU) pressurized aerosol — no mixing. Black Flag sells more than one Ant & Roach SKU (a standard water-based aerosol and a separate 'Dry' formula with a different active/propellant), so confirm the printed active-ingredient panel and EPA Reg. No. on the can in hand before relying on an exact residual claim.
Indoor / outdoor
indoor
Residual
Label residual claims vary by SKU (the 'Dry' formula markets up to several months on treated surfaces); independent testing on comparable pyrethroid contact sprays shows well under 20% mortality against German cockroaches exposed to treated surfaces, so don't treat any residual figure as an infestation-ender
Target pests
Cockroaches (including palmetto bugs), Ants (including carpenter ants), Crickets, Firebrats, Silverfish, Spiders (including black widow), Fleas, Brown dog ticks
Best job
Fast, direct-hit knockdown of ants and roaches you can see, plus a light residual on the cracks and harborage you actually spray
Active ingredient
Imiprothrin (0.100%), Lambda-cyhalothrin (0.025%)
Not for (honest)
Ending an established German cockroach infestation or a hidden ant colony — a can can't reach a nest it never touches
The technician's method

The technique walkthrough

Where DIY succeeds or fails is in the placement, patience, and the small pro moves the label never mentions. Follow the label; these are the technique details on top of it.

Easy technique~5-15 min to apply; knockdown in seconds to minutes on direct hitsTools:The can (shake before use), Gloves (optional), A rag to wipe overspray

This is an easy can to use and an easy one to waste — the whole difference is aiming into the crack and the harborage, not the open room.

  1. Confirm the SKU before you spray

    Check the printed active-ingredient panel and EPA registration number on your specific can — Black Flag sells a standard aerosol and a separately-formulated 'Dry' version, and the residual claim differs between them.

    Common mistake
    Assuming every Black Flag Ant & Roach can is identical — a reasonable guess, but the label is the only source of truth for what's actually in your can.

  2. Identify the harborage, not just the bug

    Locate where ants and roaches are actually hiding — behind and under appliances, under sinks, along baseboards, cabinet corners, and cracks around pipes — before you spray anything.

    Pro move
    Roaches cluster near moisture and food; check under the sink, behind the fridge, and along baseboard gaps first.
    Common mistake
    Spraying only the open counter or floor where you saw a bug cross — that's not where the harborage is.

  3. Shake well and hold the can correctly

    Shake the can, then hold it upright about 12 inches from the surface you're about to treat.

  4. Treat the crack, not the room

    Aim the nozzle directly into cracks, crevices, and harborage surfaces — behind appliances, under sinks, baseboard gaps — spraying until slightly wet, never to runoff.

    Pro move
    A pinpoint bead into a baseboard gap does more than fogging a whole kitchen — crack-and-crevice placement is what actually reaches where roaches live.
    Common mistake
    Broadcast-spraying an open room 'just in case' — most labels restrict this use pattern and it wastes the can while doing little.

  5. Ventilate, and keep it separate from any bait

    Let the room ventilate and treated surfaces dry fully before normal use resumes.

    Pro move
    If you're also baiting for ants or roaches, treat spray zones and bait zones as separate territory — never overlapping.
    Common mistake
    Spraying near or over a gel bait or bait station — the repellent residue drives roaches and ants away from bait they'd otherwise carry back to the colony.
Habits that decide it

Do & don't

Do
  • Check the active-ingredient panel on your specific can before trusting a residual claim.
  • Treat cracks, crevices, and harborage — not the open floor.
  • Hit visible ants or roaches directly for knockdown.
  • Keep bait and spray zones physically separate.
Don't
  • Don't fog an open room hoping to hit hidden pests.
  • Don't spray over or near gel bait or bait stations.
  • Don't treat food-prep or food-contact surfaces.
  • Don't mistake a few dead roaches for the population being gone.
The honesty moat

Where it works vs. where it fails

No product fixes everything. This is the honest boundary — the situations it genuinely handles, and the ones it simply won't.

Where it works

  • A handful of visible ants or roaches need fast knockdown
  • A specific crack, gap, or entry point needs spot-treating
  • Occasional invaders — a stray roach, silverfish, or spider — show up indoors
  • Light residual protection is useful on a treated crack between deeper treatments

Where it fails

  • Nightly or daytime German cockroach sightings point to an established, reproducing population
  • An ant trail keeps returning from a colony nesting outside or in a wall void
  • The harborage is inside a wall void or other space the spray can't physically reach
  • You're relying on the can alone instead of pairing it with baiting for real colony-level control
Don't throw money away

Mistakes that waste the product

Assuming your can matches a different Black Flag SKU's claims

Black Flag reformulates the Ant & Roach line by variant — a residual or active-ingredient claim you read online may not match the can in your hand.

Fix
Read the printed active-ingredient panel and EPA Reg. No. on your own can before making a plan.

Fogging the room instead of treating the harborage

Wastes the can, achieves little residual value where pests actually hide, and creates unnecessary occupant exposure.

Fix
Aim the nozzle into cracks, baseboard gaps, and harborage surfaces — not into open air.

Spraying over or near a gel bait or bait station

A repellent pyrethroid residue drives foragers away from bait before they can carry it back to the colony.

Fix
Keep spray zones and bait zones physically separate — treat different areas with each tool.

Treating only the roaches or ants you can see

Independent testing on comparable pyrethroid sprays found under 20% mortality against German cockroaches on treated surfaces — the reproducing population behind the wall is untouched.

Fix
Pair spot spraying with sanitation and, for an established roach or ant problem, a gel or liquid bait program.
Calibrated expectations

What to expect — and when

This is a fast knockdown tool with a light, fading residual — judge it on what you see die today, not on whether pests ever come back.

  1. Seconds to minutes

    Direct hits on ants and roaches knock them down fast — this is the product's genuine strength.

  2. First few days

    Fewer visible pests crossing treated cracks and baseboards as the light residual keeps working.

  3. 1-3 weeks

    If sightings continue or return, that's the signal the population is established and beyond what a contact aerosol can finish.

When results plateau
Results plateau fast when the population is reproducing behind a wall or in an outdoor colony: the can kills what it touches and nothing more, so persistent sightings mean the source is untouched, not that you need a stronger spray.
Know the ceiling

When to stop DIY & call a pro

A contact aerosol kills what the stream actually hits and does little for anything sheltered in a wall void or harborage. These are the honest signals the job has outgrown a spray can:

  • Roach sightings continue after 2-3 weeks of correctly aimed, harborage-focused spraying

    Independent testing on this class of product shows well under 20% mortality against German cockroaches on treated surfaces — an established population needs baiting or professional treatment, not more aerosol.

  • An ant trail keeps returning to the same spot after multiple treatments

    Recurring activity points to a large colony or satellite nests the spray can't reach — only a small fraction of foragers ever cross a treated surface.

  • You see large black ants indoors or notice rustling or frass near moisture-damaged wood

    Those point to carpenter ants nesting in structural wood — a wood-destroying pest that needs professional inspection, not a spot spray.

  • Any suspected termite or carpenter-ant activity inside structural wood

    A consumer aerosol cannot verify or eliminate a colony inside a wall or joist.

When correctly aimed spot-spraying isn't holding the line, Anchor's licensed NH technicians identify and treat the actual harborage, colony, or nest with targeted professional methods. Free inspection, same-day service across southern and central New Hampshire.

Still seeing roaches after spraying?

Get a Free inspection(603) 785-0118
Before you treat

Is it safe for pets & kids?

The short version lives here; the full per-species verdict lives on this product's pet-safety page.

This is a pyrethroid aerosol — ventilate the room during and after use, and keep kids and pets out until treated surfaces are fully dry. Never treat a suspected exposure at home.

Re-entry: Keep children and pets out of the treated area until surfaces are fully dry and the room is ventilated.

If there's an exposure, call
ASPCA Animal Poison Control: (888) 426-4435Pet Poison Helpline: (855) 764-7661Northern New England Poison Center: (1-800) 222-1222
See the full per-species pet-safety verdict for this product
New Hampshire context

German roaches and carpenter ants in NH homes

In southern and central New Hampshire, German cockroaches survive only inside heated structures, and carpenter ants — not fire ants, which aren't a NH problem despite what some national labels list — are the state's dominant structural ant. A can of Ant & Roach Killer is a fine spot tool for the odd roach behind the toaster or an ant trail on the counter, but nightly roach sightings or large black ants near moisture-damaged wood point to a bigger problem than a spray can solve. Anchor Pest Services treats the actual source across Manchester, Nashua, Concord, and the surrounding towns.

Service area

Southern New Hampshire

Anchor Pest Services · NH license #782664 · NEPMA member · family-owned since 2017.

Common questions

Frequently asked

Sources & further reading(6)
  1. [1]
    EPA Registered Product Label — Black Flag Ant & Roach Killer, Unscented (Reg. No. 9688-246)

    Verified actives (imiprothrin 0.100%, lambda-cyhalothrin 0.025%), listed target pests, aerosol format

    epa_labelverified 2026-07-14
  2. [2]
    Gordon et al., Journal of Economic Entomology (2024) — common consumer residual insecticides vs. German cockroach

    Pyrethroid liquid/aerosol sprays killed under 20% of German cockroaches exposed to treated surfaces

    academicverified 2026-07-14
  3. [3]
    University of Illinois Extension — 'DIY spray and aerosol products likely to fail in German cockroach control'

    Consumer pyrethroid sprays likely to fail against established German cockroach populations

    extensionverified 2026-07-14
  4. [4]
    UC IPM — Cockroaches (Home & Landscape)

    Insecticide sprays alone will not eliminate cockroaches; repellent residues undercut bait programs

    extensionverified 2026-07-14
  5. [5]
    UNH Cooperative Extension — Carpenter Ants Fact Sheet

    Carpenter ants nest in structural wood — a call-a-pro escalation, not a contact-spray target

    extensionverified 2026-07-14
  6. [6]
    Black Flag — Ant & Roach Killer (Unscented Aerosol) product page

    RTU aerosol format, application directions, labeled pest list (facts only, not the efficacy verdict)

    manufacturerverified 2026-07-14

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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Last updated July 2026

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