There are two very different cockroach problems misdiagnosed as the same issue. German cockroaches demand a precise, bait-and-IGR program indoors; Australian cockroaches are mostly an exterior-driven problem solved by habitat corrections and perimeter treatments. Getting the species right saves you money, callbacks, and tenant grief.
Quick ID cheat sheet
- German cockroach (Blattella germanica)
- Size: 13–16 mm; tan to light brown
- Two dark parallel stripes behind the head
- Lives and breeds indoors (kitchens, bathrooms, appliances)
- Populations explode quickly; oothecae carried by females
- Australian cockroach (Periplaneta australiasiae)
- Size: ~30–35 mm; dark brown
- Yellow margin on pronotum and distinct yellow patches on forewings
- Mainly outdoor roach; wanders inside from gardens/roof voids
- Often linked to mulch, damp gardens, subfloors, gutters
Why the species matters
German cockroach = indoor breeder
- Hides in warm, humid, food-rich micro-sites: fridge motors, dishwasher voids, under sinks, pantry hinges, behind kickboards.
- Resistant populations can develop; poor baiting or over-reliance on sprays worsens resistance and drives roaches deeper.
Australian cockroach = outdoor invader
- Breeds outdoors in mulch, garden beds, timber stacks, drains, roof cavities.
- Typically seen at night near door thresholds, bathrooms, or after rain.
- Indoor sightings often mean perimeter and structural gaps are inviting them in.
Treatment strategy: German cockroaches (precision program)
1) Inspection and prep
- Map hotspots: lift kickboards, inspect hinges, appliance voids, power points, wall cracks, under-sink pipe penetrations.
- Reduce food/grease: clean behind/under appliances; degrease rangehoods; empty overfilled cupboards.
- Ask about prior treatments: past baits/sprays affect product choice (avoid recently used actives to reduce bait aversion).
2) Core controls
- Gel baits (multiple actives, rotated):
- Apply pea-sized dots in harbourages (not open surfaces).
- Favour higher moisture/heat: hinge wells, door frames, screw holes, motor housings.
- Rotate bait families between visits to avoid resistance/aversion.
- Insect Growth Regulators (IGRs):
- Use alongside bait to break the life cycle; excellent for heavy infestations.
- Options include sprays or point-source devices in discreet locations.
- Dusts and void treatments:
- Silica aerogel or borate dusts in wall voids, kickboard cavities, and switch plates (light, targeted applications).
- Targeted, non-repellent sprays:
- As crack-and-crevice only (avoid contaminating bait placements).
- Never blanket spray kitchens—this repels roaches away from baits.
3) Follow-up and monitoring
- Schedule: 2–3 visits over 4–6 weeks for moderate-to-heavy infestations.
- Replace eaten/dried baits; move placements as pressure shifts.
- Traps/monitors to confirm population collapse, especially behind appliances.
4) Sanitation and proofing
- Nightly: clear benches, bin liners tied and removed, pet bowls lifted.
- Seal gaps around pipes and kickboards; add brush seals to pantry doors.
- De-clutter under sinks and lower cupboards; keep cardboard off floors.
[Insert image: Technician applying gel bait in a kitchen — close-up of hinge/kickboard placements]
Treatment strategy: Australian cockroaches (exterior-first)
1) Inspection outdoors and in voids
- Check garden edges, mulch, timber stacks, compost, subfloors, garages, meter boxes.
- Roof voids and gutters (leaf litter is a magnet).
- Entry points: door thresholds, window frames, weepholes, service penetrations.
2) Habitat change and proofing
- Trim vegetation back from walls; reduce dense mulch against the slab.
- Elevate/cover timber stacks; tidy storage in garages/sheds.
- Fit door seals and weather strips; screen weepholes; seal service penetrations.
3) Perimeter and void treatments
- Non-repellent barrier around the structure (skirting slab edge, weep holes, door thresholds).
- Dust or non-repellent treatments in roof/subfloor voids where accessible and safe.
- Targeted interior crack-and-crevice only if sightings persist.
4) Maintenance
- Exterior refresh every 6–12 months depending on pressure, rainfall, and garden density.
- Gutters cleared seasonally; keep yard dry and tidy to reduce harbourages.
Rentals and property sales: what I recommend
For landlords and property managers
- German cockroaches:
- Opt for a multi-visit program with bait + IGR; ask for written placement maps.
- Ensure tenancy cleaning standards are upheld; include appliance pull-out cleans when feasible.
- Australian cockroaches:
- Bundle exterior maintenance (gutters, vegetation trimming) with routine perimeter services.
- Address gaps/thresholds promptly—cheap seals prevent recurring callouts.
For sellers and buyers
- Pre-listing: German roach clearance plus two follow-ups reads well on a building/pest report.
- Curb appeal matters: neat gardens, lifted timber stacks, clear gutters signal a well-maintained envelope.
- Provide receipts/warranties for recent treatments; buyers value documented programs.
Safety and product notes
- Always follow product labels and safety directions; rotate actives to avoid resistance.
- For general pest-control guidance from the state, see the Queensland Government’s guidance on pest control for premises and equipment: Queensland Government pest control guidance
When to call a professional
- You’re seeing daytime activity (indicates high pressure).
- There are small nymphs around appliance motors or in pantry hinges (German roaches likely breeding).
- DIY surface sprays aren’t helping or seem to make things worse.
- You need discrete, food-safe control in a café/short-stay rental or a guaranteed pre-sale clearance.
Conclusion
If you want a species-specific plan and guaranteed follow-up visits, book a targeted program. For service details and bookings, see our Cockroach Control page: