Infestations in Log Homes
by Vincent Palmere
NovaGuard Technologies, Inc.

In years past, most log homes were small second summer homes and/or hunting or fishing camps. Today’s typical log home is a family’s primary residence that involves a substantial investment. With this in mind it is no wonder that log home owners are concerned about protecting their homes against wood destroying organisms.

Prior to the 1930’s, most log homes were constructed from large logs from which the sapwood was removed leaving dense, insect resistant heartwood. Most log homes are now made from fast grown pine, spruce, or fir consisting mostly of sapwood. Although some are constructed of more insect resistant wood species such as cedar, cypress, or hemlock, even these woods lose their resistance over time and become prone to infestations.

Although it is easier and less expensive to do a preventative treatment to a log home during the manufacturing process, it rarely occurs. Too many log home suppliers are reluctant to admit that their products are subject to insect and decay infestations. Some of the more responsible manufacturers have taken it upon themselves to pretreat their logs with borates, thus preventing many of the infestation problems associated with log homes.


Decay Fungi
The most serious problem associated with log homes is decay since it often leads to structural failure of the supporting logs. All too often decay problems are the result of unsound design and construction practices. Splash-back, faulty gutters, unprotected log ends, and inadequate roofs or eaves all contribute to the emergence of decay. Chemical treatments for decay should never be used to replace structural modifications correcting the initial moisture problem. However when properly applied, chemicals such as borates will stop or slow the decay process until repairs or modifications are completed.

Powderpost Beetles
Although usually referred to as powderpost beetles, most log homes are constructed from softwoods and true powderpost or lyctid beetles infest only hardwoods. The main culprits are usually anobiid powderpost beetles. Small, round emergence holes are typically found on exterior log surfaces. However, interior infestations can occur, especially in newer homes. In most cases they are a nuisance pest since it takes many years of activity for anobiid beetles to structurally damage a log. The major problem associated with an anobiid infestation is damage caused by water infiltrating into emergence holes causing rot. Since anobiid beetles prefer moist wood, moisture elimination should be a part of any control program. This includes maintaining a quality water repellent finish on all exterior wood surfaces.

Old House Borers
Old House Borers are one of the few insects that infest fairly dry wood. Although named the Old House Borer, the first emergence of these beetles usually occurs within five to seven years after construction. While log home manufacturers are often blamed for supplying infested logs, infestation can occur almost any time after the logs have been cut and the bark removed.

The first sign of an Old House Borer infestation is usually the noise made by older larvae chewing in the wood. This can be very disconcerting to the homeowner, especially in the middle of the night when larvae are most active. The appearance of oval emergence holes is the next step in the process and like an anobiid beetle infestation, most structural damage is caused by water infiltrating exterior emergence holes, thus promoting decay.

Non-reinfesting Wood Boring Beetles
Non-reinfesting beetles such as Round Head Borers, Flat Head Borers, Ambrosia Beetles, and Bark Beetles will occasionally emerge from logs within the first couple of years after construction. There is no reason to treat a home for these beetles. However, exterior emergence holes should be filled to prevent water penetration into the logs. In the case of Bark Beetles, any bark remaining on the logs should be removed for a variety of reasons. In addition to providing food for Bark Beetles, intact bark prevents the logs from drying uniformly and provides a hiding place for a broad spectrum of insect pests.

Carpenter Bees
Infestations of Carpenter Bees are occasionally a problem in log homes, especially those constructed of Western Cedar. The borates are not effective in discouraging Carpenter Bees from drilling into the wood so other measures must be taken such as the application of topical pesticides. Encapsulated pyrethroids appear to give good results but must be applied during the periods of activity. Another note about Carpenter is that they are attracted to existing holes. Filling existing Carpenter Bee holes with wood putty or caulk will significantly reduce the attractiveness of an area to more bees.


There are occasions when structural fumigation is the only solution to an infestation of wood boring beetles or drywood termites. For example, in a real estate transaction where immediate and complete elimination of an insect infestation is necessary or when it is impossible or impractical to remove a water repellent finish from the log surfaces. One pitfall when fumigating a log home is if the logs are still green or damp. Penetration of the fumigant is inhibited by moisture in the wood. The higher the wood moisture content, the less the fumigant will penetrate into the log. In other words, logs must be dry for a fumigation to be effective.

Spot Treatments
Spot treatments are rarely effective in controlling infestations of wood boring beetles in log homes. Since emergence holes are created at the end of a beetle’s life cycle, larvae may be active in many areas of the home with no visible signs of an infestation. Isolated Old House Borers can sometimes be located and eliminated using one of the wood injection systems. If the larva has already made its emergence hole, it can be used to access that particular beetle larva. Frequently an Old House Borer larva has reached a stage where it is large enough to be heard but has not yet made its’ emergence hole. In order for a spot treatment to be effective, larvae must be located within a couple of inches. The best way of locating an individual larva is by using a stethoscope and marking the loudest spot with chalk. This process works best at night when beetle larvae are most active.

Pockets of decayed wood can be treated using one of the borates. The treatment will not restore the integrity of the wood nor should it be used in place of correcting any moisture problem. Decayed areas should also be excavated and filled in with appropriate materials in order to prevent further water infiltration. 

Borate treatments
The first step before treating any log home with a borate is make sure there is no water repellent finish on the wood. Some water repellent finishes are clear and colorless, so there is no way to determine if a water repellent is present by just looking at it. The best way to determine the presence of a water repellent is to spray the wood with water. A plant mister works well. If the water beads up or does not soak into the wood within a minute or so, there is something present that will inhibit the penetration of the borate. When checking for the presence of a water repellent pay particular attention to areas under roofs, eaves, and other sections of the home protected from the sun and weather. Water repellents last much longer in these protected areas. If a water repellent is present, it must be removed by pressure washing or other means before treatment.

When interior logs surfaces are going to be treated, it is important to check them too, even if the homeowner is positive that they have never been coated. When a home has been lived in for a year or more, interior logs acquire a coating of cooking oil, especially around kitchen and dining areas. This oil residue must be removed with a strong detergent prior to treatment.

Why is it so important to remove any water repellent before treatment? First, the borate must be allowed to penetrate into the wood to get where insect larvae are feeding in order to do any good. Second, if the borate dries and crystallizes on the surface, it will create white deposits that may be difficult to remove. These deposits can usually be cleaned up with warm water but if a stain or finish has been applied over them, they are almost impossible to remove without stripping. Most log home owners are particularly demanding about the appearance of their home and do not appreciate white spots on their logs. The number one cause of complaint regarding borate treatments to log homes is not effectiveness but cosmetic damage.

Once log surfaces are cleaned and dry, a borate may be applied according to the manufacturer’s recommendations. Some people, upon learning that borates penetrate damp wood faster than dry wood, have attempted to aid penetration by wetting the logs with water just prior to applying the borate. This will not do much good since once a log is dry just wetting the surface does little to raise the interior moisture content of the wood. In addition, wetting the logs fills the surface of the wood with water, allowing less borate solution to adhere to the wood thus decreasing the amount of active ingredient being applied to the logs.

After the borate treatment is completed and the logs are dry, a paint, stain, or water repellent should be applied to all exterior surfaces. 

Results & Expectations
Borate treatments can be quite effective in preventing and eliminating most wood destroying organism infestations. However, the last stages of Old House Borer larvae are resistant to low levels of borate and can survive for several months after a borate treatment. Emergence of Old House Borers has been reported as long as a year and a half after treatment. Younger beetle larvae will be eliminated and Old House Borer eggs will not hatch in the presence of borates. Thus the reinfestation cycle will be halted and eventually the infestation will end.

EDITOR’S NOTE: NovaGuard Technologies, Inc. deals strictly with professional pest control chemical distributors.

Reprinted with permission of the author
NovaGuard Technologies, Inc.
1605 Prosser Road
Knoxville, TN 37914


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