Q. The hall in our bungalow is badly infested with common furniture beetle. This will be treated with boron and the floor replaced but my concern is the other rooms. Is the suggested treatment applied in mist form from the outside of the house through the air vents effective?

Submitted by: RT 

A. You state that the hall floor will be replaced and that it will also be treated with Boron? If it is being replaced then we would recommend that pre-treated timber is used and there would then be no need to carry out any treatment on site apart from cut timber ends. If on the other hand if the floorboards are to be replaced and the sub-floor joists and plates are to remain then these would need treating. If the boards are up then sub-floor timbers should be spray treated with a Permethrin based insecticide at a working strength of 0.2%.
 
You are right to be concerned about the flooring timbers of all other rooms which in a bungalow will mean all floors apart from the kitchen which may have a solid floor. Beneath the floor there will be little obstruction to the spread of a common furniture beetle infestation. It is almost certain that if a badly infested hall floor has been identified to the extent that timber renewal is necessary then there is a very high chance that an infestation is present in all floors. Wood boring insects do not stop because there are doors and partition walls on top of the floor. Beneath the floor as mentioned previously little obstruction is present. It is also worth pointing out that the climate beneath your floors is obviously conducive to wood boring insect attack and perhaps the timbers have a slightly increased moisture content, which wood boring insects will like, due to poor sub-floor ventilation. Consider significantly improving the sub-floor ventilation so as to change the sub-floor climate. Some refer to this as 'environmental control'.
 
In your question you query the effectiveness of applying a borate (boron) based preservative by fogging/misting it through the air vents. Let us first deal with a borate preservative for wood boring insect control. Disodium octoborate, as it is known, is what is known as a preventative form of treatment rather than curative. This is because disodium octoborate does not have any insect 'contact' killing properties - it works as a stomach poison and therefore has to be ingested for it to be effective. It is possible therefore for an adult wood boring insect to emerge through a 'boron' treated surface and survive since the adult does not 'eat' any wood and no contact killing properties are present. It will therefore 'prevent' future infestation if the correct loading (the amount of borate) is present in the surface of the timber. This is because the larval stage of the insect has to 'eat' its way into the timber and in so doing it will ingest the material. Permethrin is a preventative preservative as it has contact killing properties. Adults should not be able to exit through a treated surface or die shortly after as they would have come into contact with the material.
 
There has been much debate about fogging/misting as a means of applying a timber preservative and boric acid (a form of borate) is one of the materials known to be applied this way. Curcumin is a yellow coloured material that reacts with 'boron' by turning a red/orange colour. It takes a tiny amount of 'boron' for this reaction to take place. Some use Curcumin coated sticks as a colour reagent test to prove that the mist/fog has reached all areas which looks very impressive but be careful. All preservatives by law have what is termed 'Statutory Conditions Relating to Use' and labelling that contains application rates. It takes a huge amount of time to achieve the prescribed application rate by fogging/misting so in the real world does this happen? With regard to fogging/misting what has never been questioned is the distribution of the fog/mist but what has been questioned is the quantity or loading of the active ingredient in the surface of the timber for it to be effective.
 
We are aware that some companies will propose to fog either through air vents or by raising one board with floor coverings and furniture remaining in place. This is obviously an attractive proposition as it minimises the amount of upheaval required. It is important to note however that this method will leave the whole top surface of the floor boards without any protection at all and we would not be happy with that. Stripping a room back to the boards and raising them for conventional spray treatment is the only real way to assess the degree of infestation present otherwise how will you know?
 
For more information on fogging/misting return to our website and follow the link to Graham Coleman's web site where he has an article on the subject. It may be tempting to go down the fogging route to minimise disruption but for efficacy we would recommend the spray application of a 0.2% Permethrin based insecticide.
 
Sorry for rambling on but hope that the information is of use to you