Tuesday, November 16, 2010

Old New Zealand Housing at Risk

Are you finding more of those little holes in the wood around your home?

Spring sees the beginning of the borer flight season when the adult beetles emerge from their wooden food source to mate and start the cycle of destruction all over again. Homes in cooler and damper parts of New Zealand such Otago and Southland are most affected by these destructive insect pests but no part of the country is immune. Each year, as more damage is accumulated, our homes and other affected buildings become weaker.

It might take more than 50 years for damage to accumulate to the point of failure but the number of homes reaching such a venerable and vulnerable age is increasing. It is estimated that over six hundred thousand New Zealand homes are now over 50 years old.

Thankfully borer do not damage timbers as quickly as termites. If the slow increase in holes is noticed at all, the progress of the damage is often ignored for years. Each year the floor boards might creak a little more and the weatherboards might take a little more filling before painting; but until a floor board fails and you fall through, or the weatherboards start to rot because of water penetrating the holes, you may not be aware that your home is in danger.

Borer tend to attack softer timbers, so the older houses with structural timbers made of good quality heartwood are likely to be structurally safe, but even these houses often have decorative or non-structural timbers of softer sapwood. We often see weatherboards or floorboards riddled with borer holes next to undamaged boards. Even the same board may be heavily damaged in one area and undamaged elsewhere.
Floor board showing borer damage in lower two thirds

In the 1950s preservative timber treatment was introduced to new buildings and this has protected many timber homes of less than 60 years of age, but not all later houses used treated timbers and treatment loses effectiveness over time; it should not be expected the treatment will give protection for more than 50 years. There are many homes older than 50 years with susceptible timbers and the slow chewing of borer beetle larvae is now making more and more timbers fail. It might be too late for some parts of older houses but the borer damage can be stopped or at least slowed greatly by the use of protective borer products.

The larvae of the common wood boring beetles (Anobium punctatum and Leanobium flavomaculatum) are slow eaters; they chew through the interior of untreated timbers for 2-4 years before emerging from the wood between October and March. As they emerge they open the small (2-3mm) holes in the surface of the wood that we identify as borer infestation. When we see these holes in our weatherboards, architraves, skirting, floorboards and furniture we only see the ‘tip of the iceberg.’ The vast majority of the damage is within the timber where a labyrinth of tunnels has weakened the wood.
Borer control can be carried out effectively by the use of borer fluids that penetrate deep into the affected timbers and provide protection for many years. Even the timbers that are hard to reach such as roof timbers and floor timbers can be given protection by the use of borer bombs during the flight season. These kill the adult beetles that have emerged from the flight holes and stop them mating and laying their eggs back on the timbers. There are also aerosol injectors that can be used to treat individual flight holes in damaged painted or varnished wood. This will kill larvae deep within the wood and prevent eggs being laid in the holes.

Spring is a good time to examine your home for sign of borer infestation. I suggest looking for fresh flight holes. These will have a clean appearance inside the hole. It may take examining the holes with a magnifying lens. Sand like dust known as frass may also fall out of the flight holes when the wood is given a tap. So check your home and protect it from damage now before you fall through the floor.

A borer beetle walks into a bar. 
The bar says to the bartender. “I’m bored.”


  1. This is the thing which are harming our house.
    pest control

  2. There are worm like tracks on the surface of
    Our varnished floor boards.
    Not holes. Is this borer? Is so how do we treat
    Varnished wood?

  3. Hello,

    It is likely that the tracks are from borer and were exposed when the timbers were sanded down for varnishing. I would expect that the floor boards would be treated with borer fluid before the varnish was applied. If you are seeing new holes in the timber coming through the varnish I suggest injecting these holes with NO Borer Injector aerosol available from good hardware stores in NZ.



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