Does Source Kill Large Roach Bait by Combat actually work?

For confirmed large roaches — American cockroaches, waterbugs, palmetto bugs — yes, and hydramethylnon's slow transfer through the population is the same bait-over-spray mechanism UC IPM endorses for cockroach control generally. This product's real value is that it's specifically matched to a species most consumer roach baits ignore in favor of German-roach formulas. The honest caveat is species confirmation: use it against German roaches by mistake and results will disappoint, not because the chemistry failed but because it's the wrong bait for that pest.

Why do I still see large roaches after baiting?

The most common cause is an uncorrected moisture source or unsealed entry gap that keeps drawing new roaches in from outside faster than the bait can offset — large roaches are strongly moisture-driven and will keep arriving as long as damp basement or crawl-space conditions persist. The second common cause is too few discs, or discs placed away from the actual entry routes. If you've addressed moisture, sealed obvious gaps, used all the discs at entry points, and activity persists past two to three weeks, that's a reasonable signal to bring in a professional inspection.

How is this different from a German-roach bait station?

The active ingredient and target species are different: this product uses hydramethylnon matched to large American roaches and waterbugs, which mostly breed outdoors in moist harborage and enter to forage, while German-roach baits (often fipronil or indoxacarb) target a smaller, indoor-breeding species with very different behavior. Using a large-roach bait for a German-roach problem, or vice versa, is one of the most common ways people conclude 'bait doesn't work' when the real issue is a species mismatch — always confirm which roach you actually have.

Where should I place the discs for best results?

Concentrate discs at the routes large roaches actually use to enter — garage doors, basement window wells, utility and pipe penetrations, foundation cracks — plus interior basements and crawl spaces where moisture supports harborage. Set discs touching walls and corners rather than open floor, and use the full pack rather than a token few, since large-roach pressure often comes from multiple entry points around a foundation rather than a single spot.

Should I fix anything else besides baiting?

Yes — moisture correction and sealing obvious entry gaps matter as much as the bait itself for this species. Large roaches are drawn to damp basements, leaking pipes, and sump areas, and if those conditions stay in place, new roaches will keep entering even while the bait is working on the ones already inside. Address standing moisture and visible foundation or utility gaps alongside your baiting program for the most durable result.

How long until I see results?

Expect roaches feeding at discs near entry points to start dying within the first few days, with reduced entry and activity building over the following one to two weeks as the bait transfers through the local population, and full effect typically by one to three weeks with correct placement. A plateau before that window closes usually means an uncorrected moisture source, an unsealed entry gap, or that the species is actually German roaches rather than the large roaches this bait targets.

Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

How to Use Source Kill Large Roach Bait by Combat

Workhorse

Hydramethylnon 2.0%

Source Kill Large Roach Bait works well against American and other large roaches — the ones that mostly live outdoors and enter through basements, drains, and foundation gaps — because hydramethylnon is slow-acting enough to transfer through the population as roaches consume contaminated feces and carcasses. The technique that decides success is using every disc in the pack, concentrated at exterior entry points and interior basement/crawl-space harborage rather than spread randomly, and keeping sprays and foggers away from the discs. Expect reduction over one to three weeks as the bait transfers through the population. It is not matched to German cockroaches, a smaller and much faster-breeding species — if the roaches you're seeing are small, this is likely the wrong product, and if large-roach entry keeps recurring despite correct baiting, that points to a moisture or exclusion problem worth a professional look.

At a glance

Efficacy: Workhorse
Best job: Reducing large/peridomestic roach entry when discs are concentrated at exterior entry points, basements, and crawl spaces
Format: Enclosed large-roach bait station (disc); note that a separate, newer product branded 'Combat Source Kill MAX' for large roaches uses fipronil instead — verify the active on the box you actually buy
Technique: Easy technique

The honest verdict

Does this product actually work?

The verdict on this product

WorkhorseEasy technique

Workhorse

A workhorse for large, peridomestic roaches entering from outside — but only if you confirm the species first.

Hydramethylnon transfers slowly through a roach population in the same way UC IPM endorses for cockroach baiting generally, and this product's specific value is matching that mechanism to a pest most consumer roach baits ignore: large American roaches and waterbugs that mostly breed outdoors and forage in. Deployed correctly — every disc used, concentrated at entry points and basement/crawl-space harborage — it earns the workhorse grade for that job. Species confirmation matters here more than almost any other product in this cluster: use it against a German-roach problem and you'll get disappointing results, not because the chemistry failed but because it's the wrong bait for that species.

Best for

American/large roaches, waterbugs, and palmetto bugs entering from outside, baited at entry points, basements, and crawl spaces.

Skip it for

Heavy, established German-roach infestations — a faster-breeding, different-behavior pest that this large-roach bait isn't matched to.

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

Enclosed large-roach bait station (disc); note that a separate, newer product branded 'Combat Source Kill MAX' for large roaches uses fipronil instead — verify the active on the box you actually buy

Indoor / outdoor

both

Residual

Replace per the label interval, or sooner if activity returns

Target pests

American cockroaches ('large' or 'palmetto bug' roaches), Waterbugs

Best job

Reducing large/peridomestic roach entry when discs are concentrated at exterior entry points, basements, and crawl spaces

Active ingredient

Hydramethylnon (2.0%)

Not for (honest)

A heavy German-roach infestation — a different, faster-breeding pest matched to small-roach baits, not this product

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~15-20 min to deploy a full pack; results over days, full effect over 1-3 weeksTools:None — discs are ready to place

This bait's edge is matching the right pest to the right chemistry — confirm you actually have large roaches before you start, then concentrate discs at the entry points they're using.

Confirm the species first
Large American roaches and waterbugs look and behave differently from small German roaches — verify which you have before baiting, since this product is matched to the large species.
Common mistake
Assuming any roach is the same and baiting a German-roach problem with a large-roach product.
Use all discs
Place every disc in the pack where large roaches travel and enter — this species mostly lives outdoors and forages in, so entry points matter as much as interior harborage.
Hug walls, corners, and entry lines
Set discs touching walls and corners, under sinks, behind appliances, in basements and crawl spaces, and near foundation entry lines.
Pro move
Bait the exterior entry routes — garage, basement, utility penetrations — to intercept large roaches before they establish indoors.
Keep sprays and foggers away
Do not spray insecticide or use foggers near the discs — contamination repels roaches from bait they'd otherwise feed on.
Replace on schedule
Replace discs per the label interval, or sooner if activity returns.

Habits that decide it

Do & don't

Confirm you actually have large roaches (American/waterbugs), not German roaches.
Use all discs, concentrated at entry points and basement/crawl-space harborage.
Hug walls and corners where large roaches travel.
Keep sprays and foggers away from discs.
Correct moisture and seal entry gaps alongside baiting.

Don't

Don't use this product against German roaches.
Don't spray near or on the discs.
Don't place discs in open floor.
Don't skip sealing obvious entry gaps.
Don't expect same-day results — this is a slow-transfer bait.

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

The roaches are confirmed large/American species or waterbugs entering from outside
All discs are deployed, concentrated at exterior entry points and interior basement/crawl-space harborage
No sprays or foggers are contaminating the bait zone
Moisture and obvious entry gaps are also being addressed

Where it fails

The roaches are actually German roaches — a different, faster-breeding species this product isn't matched to
Sanitation and moisture issues that attract large roaches are left uncorrected
Only a few discs are used against real entry pressure
Spray or fogger use nearby is contaminating or repelling the bait

Don't throw money away

Mistakes that waste the product

Using this product against German roaches

German roaches are smaller, breed much faster, and behave differently than the large peridomestic species this bait targets, so results will consistently disappoint.

Fix

Confirm the species before baiting; use a small-roach bait station for German roaches instead.

Spraying near the discs

Contamination and repellent residue keep large roaches from feeding on bait they'd otherwise carry back to harborage.

Fix

Keep sprays and foggers away from bait zones entirely.

Ignoring moisture and entry gaps

Large roaches are drawn to damp basements, crawl spaces, and unsealed foundation gaps; leaving those conditions in place means new roaches keep arriving even as the bait works.

Fix

Correct moisture sources and seal obvious entry points alongside baiting.

Calibrated expectations

What to expect — and when

This bait works on a slow-transfer timeline matched to a species that mostly breeds outdoors — judge it over one to three weeks.

First few days
Roaches feeding at discs near entry points and harborage begin dying.
Days 4-14
Reduced entry and activity as the bait transfers through the local population.
1-3 weeks
Full effect; a plateau at this point usually means an uncorrected moisture source, an unsealed entry point, or that the species is actually German roaches.

When results plateau

Results plateau when moisture and entry conditions that attract large roaches are left uncorrected, or when the target turns out to be German roaches — a species this large-roach bait isn't formulated for.

Know the ceiling

When to stop DIY & call a pro

Child-resistant discs handle a light American- or Oriental-roach presence, but a heavy or German-roach population reproduces past what a fixed number of discs can control. These are the honest triggers to stop DIY:

Large-roach entry keeps recurring despite correct, dense baiting at entry points
Persistent entry after correct baiting usually means a moisture or structural gap issue that baiting alone can't fully close.
You find damp, moisture-driven harborage (sump areas, wet basements, leaking pipes)
Large roaches thrive on persistent moisture; the conducive condition needs correction, which is often a job for a professional inspection.
You suspect the roaches are actually German roaches
German roaches are a faster-breeding, harder-to-control species that needs a different bait and, if established, professional treatment.
Activity persists after 2-3 weeks of correct, dense baiting
That's enough time for hydramethylnon's transfer effect to show; continued activity suggests a source beyond consumer-density baiting.

When correct, dense baiting at entry points still isn't closing the gap, Anchor's licensed NH technicians identify the moisture source or entry pathway and treat it directly. Free inspection, same-day service across southern and central New Hampshire.

Large roaches still entering after correct baiting?

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.

The enclosed discs are child-resistant but should still be kept out of reach of children and pets — hydramethylnon is a genuine pesticide even in a small dose.

Re-entry: No general re-entry wait is required for the enclosed discs themselves, but keep children and pets from handling, chewing, or prying one open.

If there's an exposure, call

ASPCA Animal Poison Control: (888) 426-4435 Pet Poison Helpline: (855) 764-7661 Northern New England Poison Center: (1-800) 222-1222

See the full per-species pet-safety verdict for this product

New Hampshire context

Large roaches in southern & central New Hampshire

Large American roaches are a much less established indoor problem in New Hampshire than German cockroaches — NH's climate means large roaches are more often an occasional invader from a damp basement, a floor drain, or items brought in from elsewhere, rather than a year-round breeding population like German roaches maintain indoors. That makes this bait's entry-point and basement/crawl-space strategy the right honest fit for the NH pattern: correct moisture and seal gaps, and bait the routes large roaches actually use to get in. If you're finding large roaches inside regularly, Anchor Pest Services serves Manchester, Nashua, Concord, and the surrounding towns with moisture and entry-point inspection alongside licensed treatment.

Service area

Southern New Hampshire

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

Common questions

Frequently asked

Sources & further reading(3)

[1]
EPA Pesticide Product Label — Combat Source Kill Large Roach Bait (hydramethylnon 2.0%), Reg. No. 64240-2
Verified active (hydramethylnon 2.0%), targeted large-roach species, and placement directions
epa_labelverified 2026-07-14
[2]
Combat / Henkel — Max for Large Roaches product page
Product format, deployment directions, and the disambiguation between this hydramethylnon disc and the newer fipronil-based 'Source Kill MAX' (facts only, not the efficacy verdict)
manufacturerverified 2026-07-14
[3]
UC IPM — Cockroaches (Home & Landscape)
Insecticide sprays alone will not eliminate cockroaches; baits are the university-endorsed primary control tool
extensionverified 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.

Verify license

Last updated July 2026

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Professional Pest Control

When Entry-Point Baiting Hits Its Ceiling

Hydramethylnon bait genuinely works against large roaches at confirmed entry points, but persistent moisture or unsealed gaps need a professional fix. Anchor Pest Services treats the source across southern and central New Hampshire. Family-owned since 2017, NH license #782664.

Get a Free inspection (603) 785-0118

Moisture and entry-point inspection
NH-licensed applicators (#782664)
Free inspection — same-day service across southern NH

NH License #782664 · No obligation · We answer in person

Keep Exploring

How to Use Source Kill Large Roach Bait by Combat

Does this product actually work?

What it is — and what it's really for

The technique walkthrough

Confirm the species first

Use all discs

Hug walls, corners, and entry lines

Keep sprays and foggers away

Replace on schedule