Borer library
Borer bombs and sprays: what each one actually reaches
Hardware shelves carry borer bombs, brush-on fluids, injector cans and borate concentrates, and each reaches a different part of the problem. Before you spend on products, a borer inspection identifies the beetle and the timber it is in, and that decides whether any of them will work.
Updated
Borer bombs and foggers kill adult beetles in the air during the flight season, but they do not reach the larvae doing the damage inside the wood. Larvae are reached by a residual product applied to bare timber, or by an injector pushed into exit holes in painted, varnished or polished timber. Retail borer products need no licence to buy or use.
The right product depends on the surface: bare roof and subfloor timber, finished floors and furniture, and painted weatherboards each call for something different.
Do borer bombs work?
They work on one stage of the beetle only. A borer bomb or fogger fills a space with insecticide that knocks down adults flying in it, and Consumer NZ says airborne treatments kill only adults on the wing, between November and March. They do not stop the larvae, which may stay in the timber for years, so a bomb on its own will not end an infestation.
Manufacturers say much the same. One manufacturer's three-step guide uses its fogger from October to March to knock down adults before they mate and lay again, and pairs it with treating bare wood and injecting holes. A bomb is one step in a sequence: it cuts the next round of eggs while a residual product deals with what is already inside. Read the label before use and follow it, including how long to stay out and keeping pets away.
True fumigation, where a space is sealed and filled with gas, is a different thing. Consumer NZ notes it is not usually suitable for houses, because the whole area has to be completely sealed, and it leaves no residual protection.
| Product type | Reaches | Suits | Does not |
|---|---|---|---|
| Bomb or fogger | Adults in flight | Enclosed roof spaces during the flight season | Reach larvae inside the wood |
| Residual surface fluid, brush-on or spray | The bare timber it soaks into | Bare roof and subfloor framing | Get through paint, varnish or polish |
| Injector | Tunnels linked to a visible hole | Painted, varnished or polished timber and furniture | Reach tunnels with no hole |
| Borate preparation | The bare timber it soaks into | Dry, bare interior and subfloor timber | Stay put in timber that is often rain-wet |
Which borer spray works on bare timber?
A residual surface product, brushed or sprayed onto bare wood, is the treatment Consumer NZ describes as the only long-term option. It soaks into the timber and, by the makers' directions, keeps protecting it for years. It suits the bare framing in roof spaces and subfloors, which is where most live borer is found and where a brush or sprayer can reach every face.
Paint, varnish and polish block it. Consumer NZ notes the coating may need stripping before a surface treatment can work, which is rarely practical across a whole floor or wall. Kiwicare's No Borer range is the one many people search for; any product made for borer works on the same principle and is used to its own label.
How do borer injectors work on finished timber?
An injector is a small aerosol with a fine nozzle that pushes insecticide into an exit hole and along the tunnel behind it. It is the option for painted, varnished or polished timber, where a surface spray cannot soak in. Manufacturers say it kills larvae in that tunnel or close by and stops adults laying eggs in the open hole.
The catch is scale. Injecting every hole in a floor or a run of weatherboards is slow, and it only reaches tunnels connected to a hole you can see. It suits furniture and small areas; the guide to borer in furniture covers stopping a treated piece from spreading borer into the house.
What are borate borer treatments?
Borates are boron compounds, the same chemistry used in H1.2 framing, which BRANZ describes as having a long record of protecting timber against insects and decay. Borate preparations sold for borer are applied to bare timber. Because boron dissolves in water and can leach out of timber that stays rain-wet, they suit dry interior and subfloor timber better than exposed outdoor wood.
Like the other residual products, a borate cannot get past paint or varnish, so it is a choice for bare framing rather than for finished floors or furniture.
Do vinegar, kerosene and other home remedies kill borer?
None of the New Zealand references used for this page, from the NZ Farm Forestry Association and Consumer NZ to a manufacturer's technical sheet, recommends vinegar, kerosene or other household liquids for borer. There is no published evidence here on whether they reach the larvae or kill them, so they are best treated as unproven rather than as a cheap alternative.
Products made for borer are tested for that use and carry directions on the label. If cost is what pushes you toward a home remedy, compare a targeted product on the timber that needs it with the typical prices in the borer cost guide.
When is DIY borer treatment enough, and when do you need an inspection?
DIY is reasonable for small, contained problems: a piece of furniture, a few holes in a shed, or bare timber you can reach easily where the round holes point to common house borer. It is not enough when holes are oval, timber feels soft, borer is in subfloor framing you cannot see well, or you are buying a house and need a written finding.
The usual mistakes are treating the wrong surface, such as spraying painted boards, and treating at the wrong time. Bare-timber products are best in place before the adults emerge; the borer flight season calendar shows when each beetle is out. If the finding is live borer across a roof space or subfloor, treating live borer sets out what a full treatment involves.
Questions people ask
Can you treat borer yourself?
Yes, for small areas you can reach. Retail borer products need no licence, and a bare-timber product or an injector used to the label can deal with contained common house borer. Larger infestations, oval holes, soft timber and anything in a house you are buying are better assessed first, because the wrong product on the wrong surface achieves little.
When should I use borer bombs in NZ?
During the flight season, when adults are out of the wood. Consumer NZ puts house borer adults in the air between November and March, and one manufacturer sets its fogger for October to March. Outside those months there are few adults to hit. Read the label for the size of space, ventilation and how long to stay out.
Does kerosene kill borer?
There is no support for it in the New Zealand sources used here. Nothing published by the NZ Farm Forestry Association, Consumer NZ or product makers suggests using kerosene, and its effect on larvae deep in the wood is unknown. A product made for borer and applied to bare timber, or injected into holes, is the route the evidence supports.
Do I need a licence to use borer products?
No. Retail borer products such as surface fluids, injectors and fogger bombs can be bought and used by homeowners without a licence, and the borer actives in them are not on GrowSafe's list of high-toxicity products that need a specially trained handler. That makes the label the rule to follow for dose, ventilation, re-entry and pets.
Read next
- Treating live borerWhat treatment involves after a live borer finding: bare and finished timber, timing, moisture and follow-up
- Flight seasonThe months each borer flies in New Zealand, and what that means for treatment and for buyers
- Borer in furnitureChecking antiques and second-hand pieces, treating them without harming the finish, and keeping borer out of the house
- Borer costPublished Auckland prices for borer inspections and treatment, and what moves them