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Micro-spraying preservatives - myth or magic


The paper on this website 'Micro-spraying Preservatives - myth or magic', and also published elsewhere, relating to mists and fogs for use in eradicating wood boring insect infestations has drawn responses by the suppliers of such methods, and also materials. So perhaps it would now be suitable to provide a reply.



Mists, fogs or any other method of propelling small droplets from a nozzle or via an air stream are certainly not new. They are used in agriculture and for the control of stored products pests and have been so for a long time.

But what the promoters of the systems for use against active wood-boring insect infestations appear not to appreciate is that they were developed for 'space spraying' and for light surface deposits against mostly crawling insects, or those which consume the whole of the substrate such as a leaf. They are low volume or ultra low volume (ULV) application methods - they were never designed to apply large volumes of fluid to specific targeted surfaces in order to penetrate into the substrate, which is completely contrary the requirement of wood preservatives to be effective following a single application. Volume is required to penetrate the volume of wood in which the woodboring larvae exist!

The Control of Pesticides Regulations (COPR) and Control of Substances Hazardous to Health (COSHH) have also been referred to in relation to mists and the like, apparently to justify their use as a low hazard means of applying preservative. Anyone who has used in a mist/fog of any type will clearly be aware of the amount of preservative that literally floats around in and out of treatment areas and certainly the proportion that doesn't even land on timber: this applies to all such systems whether applied as a mist, fog or any dependent on air currents for their distribution. Clearly there is little control of substances hazardous to health in such application methods.

Indeed, we are told that spray 'blowers' produce reasonable directional control up to 10 metres. So will a standard spray, and probably more directional (and probably cheaper). But no one should be applying wood preservatives at 10 metres! Any directional spray will only treat the facing timber, other sides will not be treated. Therefore it is important in to move closely up and down all exposed surfaces of timbers to ensure all are properly coated with sufficient preservative to penetrate. The most cost-effective way of achieving this for single application methods is by a standard low pressure spray, and most contractors have this equipment already, they don't have to spend on specialist 'misters/blowers' which can only be used for the one purpose.



There have also been accusations made over the use of fluid applied by traditional spray methods. Such methods are accused of "drowning the building";

But note:

(1). Properly adjusted sprays do not drown the building; they can be targeted, unlike other methods, onto the wood to put the appropriate volume of fluid where it is required. Any mist/fog or what have you will contaminate non-target materials, spaces and surfaces.

(2) The application rate can be better determined since most of the fluid will actually reach the wood.



It is suggested that some of the more recent developments, including the use of surface applied non-contact insecticides, applied by micro spraying and blowing can be effective when applied as directed. We have been further told that all these are backed by reputable data which proves efficacy. Indeed, we are informed that "dozens of learned research papers have been published world wide".

But where are they relating to eradication of woodboring insects?

In reality no such data or research has been forthcoming in the public domain to support the claim that these non-contact insecticides applied by sprays or mists or what have you will eradicate wood boring insect infestations! This is completely contrary to the contact insecticides such as permethrin, cypermethrin and the older materials like Lindane and Dieldrin where a considerable amount of data is readily available. One would have thought that if such materials and techniques were the 'breakthrough' so often claimed then their proponents would certainly have published it in support of their products and methods.



The application of non-contact insecticides by surface application appear to have crept into the in-situ treatment industry with no supportive efficacy data on their ability to eradicate wood boring insect infestations. There is some data to show that on clean non-infested wood one non-contact material when applied on the surface at a loading of around 1 litre to four to five square metres did stop Anobium punctatum egg larvae surviving after hatching. It did not however prevent egg laying itself, nor did it prevent the hatching of eggs. Whilst the data show that the material applied at a specific loading would prevent attack, it cannot be extrapoated to show that it would eradicate an already active infestation (prevention is easier than cure!)

In reality common furniture beetle lay many of their eggs beneath the surface in old exit tunnels. Thus, many egg larvae do not come into contact with the material (this is discussed further HERE), and the materials will not prevent emergence. If the life cycle can't be broken then no effective control will be achieved!

Given the known and documented behaviour of common furniture beetle, the absence of published data to support the performance of non-contact insecticides as 'eradicants', then it becomes clear that there must be serious doubts over the claimed performance of such materials no matter how applied.



The favourite argument appears to be that these newer pesticides formulations are 'environmentally friendly' and far less hazardous than perhaps permethrin based materials - or so we are informed. But read the product label especially the warning phrases, hazard symbols and the statutory conditions for use, all of which must be present under the legislation covered in COPR. Compare this label with that on a permethrin product or even the earlier dieldrin or lindane based materials - there is no difference. So much for the claimed environmental problems and less hazardous use - it is certainly not stated so on the labels. Furthermore, what is the point of using environmentally friendly materials if their performance is questionable?

One final point. It is quite common to relate the toxity of one material to another using the LD50 figure. This is fine except that in some case whilst the 'new' material has a higher LD50 figure (lower mammalian toxicity), it is used at 25 - 50 times greater concentration!



So perhaps the so-called 'progress' in application methods such as misting, fogging, blowing, and the introduction of surface applied non-contact insecticides are not the 'bee's knees' of development.

As for the surface applied non-contact insecticide claims to eradicate wood boring insects infestations, contractors and clients alike should ask suppliers for validated performance data before they buy and use them - and make sure that such data refers to eradicant treatment, not any form of pre-treatment or full impregnation process.

And if you manage to be provided with this data or one of the "dozens of learned research papers published world-wide" which specifically covers surface applied eradicant treatments, then please could you let this author have a copy because searches of research literature, or suppliers including raw product manufacturers, has not provided any - possibly because they don't exist?


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