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Treatment for Drywood Termites

There are several alternatives for dealing with drywood termite infestations or damage, depending on the extent of the problem. This places great importance on an extremely accurate inspection of the structure.

Option 1) No Control the Termites

Where the infestation is slight or damage is cosmetic and limited to one or two small areas, you may choose not to use any control measures. Drywood termite colonies often develop slowly; therefore, the costs incurred with some control measures may not be warranted. But if you choose not to control, be sure to maintain a monitoring program so you’ll know when and if control becomes necessary.

Wood Replacement of Termite Damaged Timbers

Where the infestation is limited, remove and replace damaged wood, preferably with pressure-treated wood that will protect against both termites and wood decay. Or it may be more practical to have a pest control operator apply special formulations of wood preservatives. They penetrate fairly deeply into unpainted wood surfaces, particularly cut ends and structural joints. Certain precautions are necessary to protect ceilings and painted surfaces from staining.

Termite Fumigation.

If infestations are widespread or suspected in areas that cannot be inspected or replaced (such as in wood shingles, between walls or in eaves or attics), fumigation is a control alternative. First, a structure is completely enveloped in gas-proof tarpaulins or heavy plastic sheeting. Masonry construction with flat, composition shingle roofs may be sealed around the doors, windows and vents. Then a fumigant gas is released into the structure. The gas penetrates into cracks, crevices, void areas and directly into wood to kill termite colonies. Lethal concentrations are contained by the tarpaulins long enough to permit uniform penetration deep into all infested areas.

Despite its effectiveness, there are disadvantages to fumigation. It does not leave any chemical residue to deter future infestation. Fumigation is extremely hazardous and the occupants of the home may have to vacate for several days. Also, fumigation is labor intensive and requires the specialized knowledge of a licensed, professional pest control firm and can be expensive. Fumigation requires special certification because of the extreme hazard. It is imperative to remove all household pets, plants and food products from the home prior to treatment.

The following information is provided to help you choose a suitable termite treatment program.

Summary of Drywood Termite Control Options

Treatment Efficacy Considerations Damage to Home
Fumigants* >99% Must vacate, expensive, utility company must shut off/turn on all gas – requires extensive coordination. Highly regulated and only minor damage if done right, but can lead to death (if house entered before gas has dissipated fully. Roof tile damage (get roof tile insurance), damage to plants under tarp.
Heat* >95% Must vacate, expensive, extinguish pilot lights, no chemicals used Can be a problem for electronic equipment, toilets sealed using wax rings
Chemical treatment of wood post construction Varies depending on chemical and application Residual protection good but only in the specific areas treated Some drilling may be required
Liquid nitrogen* >90% Benign material Some drilling may be required
Biological control Data required No chemicals used Unknown
Electrocution* 10-99% No chemicals used More effective when more holes are drilled
Microwaves* 90% No chemicals used Possible heat damage
Physical barriers Data required No chemicals used Pre-construction incorporation
Pressure-treated wood Data required Long term protection Pre-construction incorporation or can be used to replace damaged materials

*Efficacy data presented was taken from Lewis, V.R. & M. I. Haverty. 1996. Evaluation of six techniques for control of the western drywood termite (Isoptera: Kalotermitidae) in structures. Journal of Economic Entomology 89:922-934. The study was conducted on a simulation home (stucco and wood construction), with an attic and crawl space.

Whole-Structure Termite Treatment

Fumigants (methyl bromide and sulfuryl fluoride) treat all infestations simultaneously, and have high levels of control, usually reaching 100% if correctly applied. Major issues to be considered by pest control companies include the difficulty of installing tarpaulins, the difficulty in determining the correct dosage, the need to protectively seal food items, and the lack of residual control. People, animals and plants must vacate structures for 1 to 2 days to allow for treatment and ventilation.

Heat is a nonchemical option for whole-structure treatment. The treatment process involves heating all wood in the structure to a minimum of 124°F and holding this temperature for at least 30 minutes. The benefit of heat treatment is the ability to treat the entire structure without the use of chemicals and the relatively short period of time the structure must be vacated (several hours). An additional advantage is that portions of large structures can be treated separately, which is very useful in apartments and condominiums. The major drawback to using heat is that certain areas within a structure may be difficult to heat, such as wood on concrete (called a heat sink). Other issues to consider include the possible damage to sensitive items in homes.

Localized or Spot Treatments for Drywood Termites

There are many localized/spot treatment methods available that include both chemical and nonchemical options. The chemical options include liquid organophosphates and pyrethroids, borate and silica gel dusts, and liquid nitrogen. For the liquid and dust insecticides to be effective, they must be touched or ingested by termites. Best results are obtained by drilling into the termite galleries and injecting products directly. Liquid nitrogen is different from the other spot treatment methods in that its mode-of-action is thermal; it causes a sudden drop in temperature, which kills the termites. Laboratory studies have shown that 5 minutes at -5°F kills drywood termites.

Microwave devices are also available for drywood termite control. Microwaves kill termites by causing fluids inside their cells to increase in temperature, which destroys the cell membranes. Advantages of microwaves include relative portability; and a nonchemical nature. When using microwaves, however, detection accuracy is critical to success. Both microwaves or heat treatments may damage the surface or interior of wood boards, depending on the power of the device. As with heat treatments, it may be difficult to heat areas with heat sinks to high enough temperatures with microwaves for effective control. Microwave devises are limited to certain areas because it may be impossible to use the device in small spaces, behind cabinets, etc.

High voltage electricity, is another nonchemical option for controlling drywood termites. The device currently marketed uses high voltage (90,000 volts), but low current (< 0.5 amps). The advantage of electrocution is that the equipment is portable. The limitations include detection accuracy and access to the entire collony. If drill holes and copper wire are used to enhance the flow of current into wood, minor damage occurs to wall coverings, walls, and structural wood members.

Minor damage to the structure occurs from the holes drilled for spot treatments of chemicals and for liquid nitrogen insertion. For all spot treatments, it is critical that all infestations in a structure are detected so that they all receive treatment.

Wood replacement is another remedial treatment option. However, similar to the other spot treatments, its effectiveness is highly dependent on detection accuracy and extent and location of the infestation, and it may be expensive to accomplish.

There is little information on biological control of drywood termites. Biological control is the use of other life forms (e.g., insects, nematodes, or microbes) to control pest insects. Currently research and development of biological control agents is underway with the possibility of commercial products being available sometime in the future.

It is currently unclear how effective pressure-treated wood (chemically treated wood that is brown or green in color) will be for drywood termites. Painting also affords protection. Double coats of paint increases protection and epoxy enamel paint appears to be the most effective protection against drywood termites.

Dampwood termites

dampwood termite picture Are controlled by the same methods as drywood termites when they are in wood not in contact with the ground. Where there is ground contact, structural changes to eliminate moisture may be necessary, together with ground treatment as recommended for subterranean termites. However, control consists primarily of eliminating the moisture problem in the wood, often involving replacement of damaged and moist wood.

Subterranean Termite Treatment Methods

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