Woodworm treatment: how to choose the right one

Have you found holes in your furniture or in the rafters of your roof when you thought you would never have woodworm problems? Or have you already carried out a woodworm treatment but shortly afterwards found new holes in the wood?

Are you thinking that you have so far received bad advice and wasted your money on ineffective wormwood treatment products? I have some bad news: you may be right. However, this does not mean that the woodworm problem cannot be solved!

What you will find in this article is a detailed analysis of woodworm treatments, which will allow you to understand which may be the best solution to eliminate woodworm in your specific case.

Wood is a natural material that has its own intrinsic durability, which varies not only from species to species but also between mature wood (heartwood) and younger wood (sapwood) of the same species. Natural durability is influenced by the presence of substances called 'extractives' and conditions the damage that woodworms and termites - termed xylophagous insects - can produce. The term xylophagous refers precisely to the fact that these little animals use wood as food (from the Greek xýlon 'wood' and phagèin 'to eat').

In general, it can be said that the sapwood is the area of wood most easily subject to biotic degradation because it contains sugars, starches, amino acids and mineral salts that act as nutrients for insects (especially Lyctids). 

Heartwood extractives - polyphenols, tannins, terpenoids and tropolones - on the other hand, are toxic to xylophagous organisms, but it should be remembered that the type of substances and the quantity contained in the wood vary from species to species. There are also wood species defined as having 'undifferentiated heartwood' because in them the heartwood has the same durability as the sapwood: these include fir, poplar and beech.



Natural durability of some wood species used in Italy (NR = not resistant, MR = moderately resistant, R = resistant, * = heartwood is also attacked)

It must be borne in mind that the quality of wood and people's lifestyles have changed a great deal in recent decades. This has also led to a change in the habits of the insects themselves, which today can sometimes be found in wood materials (e.g. plywood or veneer) that were previously very unattractive to woodworms. 

As can be seen in the table above, there are no wood species that can resist all xylophagous insects.  
Carrying out a preservative treatment therefore means increasing the durability of the wooden element, so as to ensure greater protection and resistance to biological attack. The treatment can be carried out to eliminate woodworms or termites that are already attacking the wood (in this case we speak of curative treatment) or to prevent new settlements (preventive treatment).

Depending on whether one wants to carry out a preventive or curative treatment, there are different methods of pest control: physical methods include microwave and hot air treatment, while chemical methods may involve the use of gas or liquid woodworm treatment products.

With the first three methods listed above, the elimination of woodworm and/or termites is achieved only when the insects are already present in the material: the efficacy ceases at the end of the pest control, so the wood may be attacked again if a preventive treatment is not carried out, which can only be done by using of woodworm treatment products.

The first three types of treatment can only be carried out by qualified and experienced personnel, while pest control with liquid products can also be do-it-yourself: you can buy a woodworm treatment product at the hardware store or on the Internet.

Let us look in detail at the various types of treatment.

Microwave woodworm treatment is based on the absorption of electromagnetic energy by wood, whose chemical structure is characterised by the presence of water molecules. 

The effectiveness of microwave treatment depends essentially on two factors:

•    wood moisture;
•    wood thickness.

What is the mechanism behind the treatment? Water molecules are polar which means that they are able to orient themselves if they are in the presence of an electric field (this is the so-called polarisation phenomenon). Microwaves are able to exert forces on the electrical charges of water molecules, causing them to vibrate. By vibrating, the molecules rub against each other and heat up through friction.

Water is therefore of fundamental importance in microwave woodworm treatment: the greater is the amount of water in the wood, the more it heats up (the same principle is used when cooking food in a microwave oven!). 
However, it must be remembered that the absorption of electromagnetic energy decreases as the depth of the material increases, and the maximum depth of treatment decreases as the moisture content increases. Usually, mortality of larvae, eggs and pupae can be achieved in wood several centimetres thick. 

When using this technique, attention must be paid to any metal parts that may be present in the material to be treated (e.g. nails, screws, hinges). Metal objects are very good conductors of electricity: electric currents that strike a conductor can cause a rise in temperature, which can lead to localised overheating or even burning. 

Generally, for microwave treatment, a device called a 'magnetron' is used, which generates energy with a frequency of 2450 MHz, the most useful for causing interactions with water and corresponding to a wavelength of 12.25 cm. The heating occurs rapidly and must be maintained for several minutes to ensure 100% mortality of the larvae. Usually, the temperature of the insects is raised to around 55 °C (smaller larvae can also die at around 52-53 °C), while the wood does not exceed 45 °C. This temperature difference occurs due to the fact that woodworms and wood have different thermal and electrical properties.
It is possible to carry out a local treatment, using an applicator, or a general treatment in a reverberation chamber.

Hot air woodworm treatment is based on heat conduction inside the wood. 
How does it exactly work? Generators produce air at approx. 80-100 °C, which is conveyed to the area to be treated through large-diameter pipes. The heat flow must be maintained for such a time that the material as a whole reaches a temperature of around 55-60 °C. 

This method is generally used to disinfest wooden attics, but these must be sealed with thermal blankets beforehand to prevent heat loss during treatment. 

Gas treatment refers to a type of pest control that, although effective because it could reach even the most difficult to treat areas, has now fallen into disuse because it involved the use of toxic gases such as methyl bromide, phosphine or hydrogen cyanide. Regulation (EC) No. 2037/2000 on "Substances that deplete the ozone layer" banned the production of methyl bromide (the gas most commonly used for woodworm treatment) as of 1 January 2005, precisely because this substance was considered, along with others listed in the European standard, to be responsible for depleting the ozone layer.

Modified and controlled atmosphere treatments with low oxygen content have become a viable alternative to the use of toxic gases, especially for the conservation of cultural property. Xylophagous insects are eliminated by anoxia, i.e. by suffocation due to the lack of oxygen. It must be borne in mind that this type of treatment must take a sufficiently long time as the larvae, when in an environment that is adverse to them, are able to protect themselves by suspending breathing for some time.

There is a close correlation between treatment time, temperature and relative humidity. Both the environmental situation of the wood to be treated and the metabolism of the larvae, which must be in full activity, must be taken into consideration, otherwise the anoxia technique is ineffective. Generally, temperature conditions between 21 and 25 °C, with a relative humidity of 60-65% can be considered suitable. 
The treatment time varies depending on the temperature. For example, if a gas mixture containing nitrogen (86%), carbon dioxide (13%) and oxygen (0.7%) is used and the treatment is carried out at a temperature of 21 °C, mortality of Anobidi larvae can be achieved after 30 days of treatment, whereas at a temperature of 25 °C, 21 days may be sufficient. 
During the treatment period, the oxygen concentration in the room or cell used for the purpose should always be between 0.1% and 1%.

As we said at the beginning, with the methods listed so far, the elimination of woodworm and/or termites is only achieved when the insects are already present in the material. We are therefore talking about curative treatments whose effectiveness ceases once the pest control is complete. 
With liquid products, such as Lignum AT-KS, on the other hand, it is also possible to carry out preventive treatments, which prevent the xylophagous organisms from laying eggs and colonising the wood.



How do these woodworm tratment products work? The action occurs through contact with the product or ingestion of the treated wood. 

 The best woodworm treatment product:
•    contains an effective biocide active ingredient;
•    is able to penetrate deep into the material;
•    is easily applicable;
•    does not give off unpleasant odours;
•    does not grease;
•    does not affect paints, pigments, coatings, glues and hardware.

Why is it important that the woodworm treatment product penetrates deeply? 
•    Because the larvae dig tunnels wherever they find palatable wood that allows them to feed and thus grow. 
•    This is because the biocide active ingredient can undergo degradation processes due to light and heat, so the deeper it goes, the longer it lasts.

There are water or solvent based woodworm treatment products on the market: let us see how the two types differ.

As we have seen, the effectiveness of woodworm treatment products is guaranteed both by the biocide active ingredient - in most cases permethrin - and by the depth of penetration provided by the solvent (water or an organic solvent). We have said that the best woodworm treatment product is the one capable of going deeper and it is precisely because of this characteristic that the two types of product differ: water usually has a lower penetration capacity into the wood than organic solvents. 
Moreover, it is worth remembering that in order to guarantee preventive or curative efficacy, the product must always be applied in the quantities indicated on the label; this means that lifting of the wood fibre could occur when applying several coats of water-based woodworm treatment product.
Not everyone knows that permethrin is insoluble in water, so in order to be contained in a water-based biocide product, it must be carried by a cosolvent, i.e. a substance (usually an organic compound) that when added to the primary solvent (in this case water) increases the solubility of the poorly soluble or insoluble compound (permethrin).

You may have wondered about the best time to apply woodworm treatment product or under what circumstances it should be used.
As soon as new holes appear in the wood and we find rosume (saw dust) on the ground or on the material we can assume that there is an infestation in progress. What is difficult to understand is the extent of the attack, because the holes (called 'flicker holes') that we see on the surface are the result of adult insects escaping. They, in their previous state as larvae, need to feed by digging tunnels in the wood in order to grow and then reproduce.



If you buy an antique object that has holes in it, how can you tell if the material is actually being attacked by woodworms? Observing the colour of the wood can help. Once any rosume left in the hole has been removed, if the wood you observe is light-coloured, it means that the woodworm has probably flickered in a recent time. If, on the other hand, it’s dark, it means that the wood had time to oxidise and therefore the hole could be at least a few years old.  
If the person who sold you the artefact cannot certify that he or she has disinfested it, then it is a good idea to carry out a curative treatment to dispel any doubts and to be comfortable for a relatively long time.

Why do we talk about 'relatively long' time? Because woodworm treatments are not eternal. In general, a wood preservative should be applied every 10 years as a preventive measure, especially if the material has suffered attacks by xylophagous insects in the past.

Treatment with an anti-wormwood product can be carried out at any time of the year, but usually the best and most immediate results are obtained in spring, i.e. in the period when the larvae resume their activity.
Spring is also the best time for modified and controlled atmosphere treatments, as we have seen above, while microwave or hot air treatments can be done in any season.

As we have already mentioned, woodworms feed on wood, so furniture, parquet and beams that may be present in our homes are especially attractive to them. 
We can also find woodworm in picture frames and mirrors, in skirting boards and wicker baskets.

Treatment with products against woodworms can be carried out on any wooden artefact or structure. The method of application should be chosen according to the objects to be treated: for furniture, frames and small objects, brush and injection treatments are easier, while for floors, beams and structures, spray application is certainly easier.



It is always advisable not only to treat the material in its entirety, but also to apply the product on all those wooden elements that are present in the same environment, even if they do not appear to have been attacked: the adult insect is in fact capable of flying and the female may lay her eggs in the same wood from which she has flickered or in other artefacts or structures.

Microwave treatment can also be carried out anywhere, being very careful of metal parts, as we explained earlier. 
Hot-air treatment is usually used to disinfest wooden attics, which must, however, be sealed beforehand.
Modified and controlled atmosphere treatments with low oxygen content are mainly used for the conservation of cultural goods. The treatment can be carried out in cells designed for the purpose or in the rooms where the works to be treated are kept.

A banal but very important premise should be made. When you buy a woodworm treatment product and decide to do a DIY treatment, you must always read the packaging label to know its specific characteristics and how to use it. Also remember that the product's yield must always be respected. In order to guarantee the preventive or curative effectiveness of the treatment you must ensure that you apply the quantity of biocide active ingredient that the manufacturers indicate. 
The data provided on the label are the result of research and testing; if we decide to apply the product arbitrarily, we should not be surprised if the treatment does not yield the desired results.

Before pest control, it is good practice to thoroughly clean the surfaces in order to achieve better absorption of the product and thus better effectiveness. If possible, the flicker holes should be emptied of any rosume left by woodworms.
The amount of product to be used depends on the type of treatment, which can be curative (if the insect attack is already underway) or preventive (if you want to prevent the insects from attacking the wood).

Liquid woodworm treatment products, such as Lignum AT-KS, can usually be applied by injection, spraying, dipping or brushing.

Injection application can be used in combination with brush or spray application. It consists of injecting the product with a syringe through the flicker holes on the surface (if the wood has already been attacked by xylophagous insects). In this way, the product penetrates deep into the galleries created by the larvae. However, it must be borne in mind that the larvae often close the previously created galleries with their own rosume, so it is not always easy to make deep injections into the wood. Alternatively, natural cracks in the wood can be exploited, if present.
This method must be complementary to others because syringe application alone does not allow the product to be evenly and completely distributed throughout the material. In fact, injection treatment is usually performed for small objects and when the number of holes is limited because the work is very time-consuming. 

Spray application (low pressure) is widely used as it allows even large surfaces, such as structures, to be treated in a relatively short time. It is possible to pass over the treated surfaces with a brush afterwards, if you want to insist with product absorption on the most critical areas (especially in the case of furniture rich in mouldings).



The immersion technique can be used if small artefacts have to be treated.
Brush application can be used as the only way to apply the product, especially if you need to treart small objects. This can be combined with the injection method, as we explained earlier.



Remember that it is also good to apply the product on all those wooden elements that are present in the same environment as the infested object, even if they appear to be in perfect condition, since the adult insect flies and the female may deposit its eggs in the same wood from which it has flickered or in other objects.

At the risk of being repetitive, we would like to remind you that it is important to read the label of the wormwood treatment product you want to buy. Why is this concept so important to us? The answer is simple. The label contains all the information about the product's characteristics, its performance, how to use it, its content and specific hazards. A consumer who informs himself is an informed consumer, who knows what he has bought and how he should use the product.

How can you tell if the wormwood treatment product you receive is a product that meets the standards and is therefore legally placed on the market? 

Annex V of Regulation (EU) No 528/2012 lists the types of biocidal products by group and product type. Product-type 8 (or PT 8) identifies wood preservatives, i.e. “products used for the preservation of wood, from and including the saw-mill stage, or wood products by the control of wood-destroying or wood-disfiguring organisms, including insects”.
In 2014, Commission Implementing Regulation No. 1090 was issued approving the use of permethrin as an active substance in biocidal products of types 8 (wood preservatives) and 18 (insecticides, acaricides and products intended for the control of other arthropods). 

Woodworm treatment products that contain only permethrin must therefore follow the guidance given in the regulation on the 'Classification, packaging and labelling of biocidal products' (Art. 69).
Let us look together at what information a permethrin-based woodworm treatment product must mandatorily display on the label (but which it would not be bad to also find in the technical data sheet):

1. Authorisation holders shall ensure that biocidal products are classified, packaged and labelled in accordance with the approved summary of biocidal product characteristics, in particular the hazard statements and the precautionary statements, as referred to in point (i) of Article 22(2), and with Directive 1999/45/EC and, where applicable, Regulation (EC) No 1272/2008. In addition, products which may be mistaken for food, including drink, or feed shall be packaged to minimise the likelihood of such a mistake being made. If they are available to the general public, they shall contain components to discourage their consumption and, in particular, shall not be attractive to children.   

2. In addition to compliance with paragraph 1, authorisation holders shall ensure that labels are not misleading in respect of the risks from the product to human health, animal health or the environment or its efficacy and, in any case, do not mention the indications ‘low-risk biocidal product’, ‘non-toxic’, ‘harmless’, ‘natural’, ‘environmentally friendly’, ‘animal friendly’ or similar indications. In addition, the label must show clearly and indelibly the following information:


(a) the identity of each active substance and its concentration in metric units; 

(b) the nanomaterials contained in the product, if any, and any specific related risks, and the word 'nano' in brackets after each reference to nanomaterials; 

(c) the authorisation number allocated to the biocidal product by the competent authority or the Commission; 

(d) the name and address of the authorisation holder; 

(e) the type of formulation; 

(f) the uses for which the product is authorised; 

(g) the manner of use, frequency of application and dose, expressed in metric units, in a manner that is meaningful and comprehensible to the user, for each type of intended use under the terms of the authorisation; 

(h) details of probable direct or indirect adverse reactions and any instructions for first aid; 

(i) if an instruction leaflet is enclosed, the words 'Read the enclosed instructions before use' and, where appropriate, warnings for vulnerable groups; 

(j) instructions for the safe disposal of the biocidal product and its packaging, including, where applicable, any prohibition on the reuse of packaging; 

(k) the batch number of the formulation or designation and the expiry date under normal storage conditions; 

(l) if applicable, the period of time needed for the biocidal effect, the interval to be observed between applications of the biocidal product or between application and the next use of the product treated, or the next access by man or animals to the area where the biocidal product has been used, including particulars concerning decontamination means and measures and duration of necessary ventilation of treated areas; particulars for the specific cleaning of equipment; particulars concerning precautions to be taken during use and transport 

(m) where applicable, the categories of users to which the use of the biocidal product is restricted; 

(n) where applicable, information on any specific hazards to the environment, with particular regard to the protection of non-target organisms and provisions to avoid water contamination; 

(o) for biocidal products containing micro-organisms, the labelling requirements of Directive 2000/54/EC.

As you have just read, in paragraph 2 of Art. 69, the label cannot bear the "wording 'low-risk biocide', 'non-toxic', 'harmless', 'natural', 'environmentally friendly', 'animal friendly' or similar wording" because to do so is to create misleading communication. Woodworm treatment products are dangerous precisely because of their specific biocidal action: there can therefore be no such thing as a non-toxic woodworm treatment product.

The regulation also requires that the authorisation number assigned to the biocidal product be shown on the label. 

Are you now convinced that it is important to read the label of the woodworm tratment product? 

 If you don't have time to go to the hardware store or the paint shop to evaluate the various products, you can also do some research in front of the computer: you can find the technical data sheets on the Internet, which usually contain all the information you need to understand whether the product is legal and can solve your problem. To avoid surprises once you have purchased the woodworm treatment product, be wary of those who show very little information on their website, do not provide the product's technical data sheet and do not mention European Regulation No. 528/2012.

Microwave, hot air or modified and controlled atmosphere woodworm treatments are not subject to biocide legislation because they do not use biocidal active ingredients. This does not detract from the fact that these methods must still comply with current regulations on safety for humans and the environment.


We hope with this article we have clarified your ideas on woodworm treatments. If you have any other questions or curiosity, please do not hesitate to write to us!

 

Bibliography:

• Funghi e insetti nel legno, A. Gambetta, Nardini Editore

• Gli insetti e i danni del legno, G. Liotta, Nardini Editore