Time to treat borer is now
Borer is a common problem in New Zealand and spring and summer, when the tiny woodeating insects emerge from their timber burrows to breed, is the ideal time to take action against infestations.
The most common form of DIY borer treatment is usually only effective a few millimetres from the surface of the wood and when ingested by the beetle.
Given that for much of the three or four years the borer spends inside the wood it is far from the surface and not eating but clearing room for its larvae to grow, now is the best opportunity for the home handyman to act.
The process should start with a careful inspection, because while borer holes with fresh piles of sawdust indicate action within, in many cases the holes found will be historic.
The most popular treatment able to be applied without a licence is what is often referred to as a ‘‘wood preserver’’, which typically has boric acid and boron as its active ingredients. Sold as a powder, it can be wetted and painted onto timber.
The product is safe to use, however it must be eaten by the borer to be effective. Because it can’t be mixed with solvents, it doesn’t penetrate deeply into the timber, and it also tends to break down relatively quickly with moisture and sunlight. As such, it is mainly a warmseason treatment, targeting borer as they emerge to breed and return to lay eggs.
Most professional pest control businesses will use a water-applied insecticide. These require a licence. A very limited amount of solvent is added to the mix, which means there is little fire risk. However, it also means penetration into the timber is limited.
Such insecticides do have the advantage of killing borer on contact, though, and are usually fortified against the deleterious effects of sunlight and moisture.
The most effective – but rarely used – treatment is a solvent-suspended insecticide. This will penetrate deep into the wood in a matter of hours, killing on contact and putting a quick end to infestations.
The downside is higher material costs and the need for special equipment to mitigate the fire risk of working with the solvents, which can make this an expensive approach for many.
Borer are often found in a home where moisture content is high and where timber is untreated, such as in the subfloor and ceiling spaces of older homes.
Professional advice is recommended in the first instance. Given New Zealand’s large number of older timber homes, this is usually easy to find.
Borer leaving their burrows to breed, as indicated by small piles of sawdust outside their holes, are the easiest to eradicate with DIY treatments, which are usually only effective when borer consume wood at the surface.