Rudolf H. Scheffrahn and Nan-Yao Su, Professors of Entomology
University of Florida Wood-Destroying Insects Unit
Fort Lauderdale Research and Education Center
3205 College Avenue, Davie, FL 33314
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Many residents of Florida, especially those living near the
coast or in southern counties, will experience a drywood termite
infestation in their home. Unlike subterranean termites which
require excess moisture, drywood termites spend almost their
entire life cycle inside the sound, dry wood members upon which
they feed. Only during brief swarming flights do young adults
leave the confines of their galleries to begin new colonies
elsewhere. Winged adults or "swarmers",
shed wings, ejected pellets,
and galleries inside wood are typical
signs of a drywood termite infestation. Swarming ants are sometimes confused with termites,
but their differences are easy to recognize.
If a drywood termite infestation is suspected in your house, a thorough examination of the entire structure should be conducted by a pest control operator or building inspector. To provide a valid report, the inspector must hold a State-issued wood-destroying organism inspection card and be personally licensed in the termite category or be supervised by such a licensee. A careful inspection is critical in order to determine the extent of an infestation and location(s) of other possible drywood termite colonies. The results of the inspection will dictate the best treatment option(s) as no single control method is best for all situations. Most companies offer only one or a few of the methods discussed herein, therefore, it is prudent to contact several companies for inspections and treatment recommendations before choosing the company and specific treatment which best fit your needs.
Drywood termite treatments are divided into three general
categories which reflect their areas of coverage: whole-structure, compartmental,
and local or "spot"
applications. Preventative treatments are also available and are
usually offered after an existing infestation has been treated. All
treatments listed below will kill drywood termites, but their
effectiveness is limited when used beyond their intended scope.
|Treatment||Unit of Coverage||Time per Unit|
|Fumigation||entire structure||1-2 days|
|Heat||several rooms, attic, an apartment||4-12 hours|
|Cold||wall voids between studs||30 min|
|Electrocution||3-4 ft of board||2-30 min|
|Microwaves||1-4 ft of board||10-30 min|
|Drill-and-Inject||3-12 ft. of termite gallery||5-20 min|
|Borate Surface Spray||raw wood surfaces||10 min - 2 hours|
|Wood Replacement||removed wood member||highly variable|
IMPORTANT ADVANTAGES AND DISADVANTAGES OF DRYWOOD TERMITE TREATMENTS
|Fumigation||complete eradication of termites in entire structure||overnight evacuation and food protection required|
|Heat||eradication where heat is confined||all heat sensitive materials must be removed from area|
|Cold||eradication where cold can be confined, usually a wall void||holes drilled in wall for injection of liquid nitrogen|
|Electrocution||maneuverable device||no ability to measure lethal application|
|Microwaves||control without drilling||poor maneuverability for confined areas|
|Drill-and-Inject||long tract record, residual chemical delivered directly into termite gallery||drilling of infested wood required|
|Borate Surface Spray||large coverage possible, residual protection||only unfinished wood treatable, drilling of infestated wood recommended|
|Wood Replacement||absolute removal of infestation||infestation may run into adjacent, more difficult to remove, wood members|
Fumigation. Fumigation ("tenting") has been
the only method used for over forty years which insures complete
eradication of all drywood termites from a structure. The
phase-out of methyl bromide in the U.S. has positioned sulfuryl
fluoride (VikaneŽ) as the leading gas fumigant. Fumigation is a
highly technical procedure which involves surrounding the
structure with a gas-tight tarpaulin, releasing the gas inside
the seal, and aerating the fumigant after a set exposure time.
Before fumigation, the homeowner must remove all plants and
animals from the house, remove or place food items inside special
protective bags, and insure that there is sufficient tarp
clearance between sensitive landscaping and exterior walls. The
fumigation company may monitor gas concentration during the
fumigation to insure that a sufficient dose is maintained. Only
after the house has been aerated and tested for absence of
fumigant can it be reoccupied. Because the fumigant is a true gas
and works as a component of air, no cleanup of clothing, dishes,
floors or other surfaces is needed.
Heat. Because of technical challenges, heat treatments
in Florida are usually not applied to entire buildings, but are
limited to known areas of infestation (see below).
Heat. Heat treatments are used to eradicate drywood
termites from portions of a house such as an attic, porch, or
bedroom, or from an individual apartment or condominium unit
inside a multi-family dwelling. Heat sensitive articles are
removed and the infested area is cordoned off with polyethylene
or vinyl sheets. Temperature probes are placed in the
hardest-to-heat locations and heat is applied with a high-output
propane heater. After a lethal target temperature is achieved,
the area can be cooled quickly for immediate reoccupation. If a
heat liable material cannot be removed, it must be thoroughly
protected with insulating blankets.
Cold. Excessive cold is primarily used for treating
wall voids or similar small enclosures in a structure. Liquid
nitrogen is pumped into these voids until the temperature drops
to a level lethal to drywood termites. Temperature probes should
be used to insure that lethal temperatures are attained. During
treatment the area must be monitored for safe oxygen levels.
Wood Injection. Wood injection or
"drill-and-treat" applications have been used since the
1920s to treat drywood termite infestations which are accessible
and detectable. An insecticide is injected into small holes
drilled through any wood surface into termite galleries
delivering the treatment directly to the pest population. This is
the simplest and most direct method of treatment. The amount of
drilling required and the effectiveness of this treatment depends
on the chemical used and the nature of the infestation. Most
chemicals will remain active in the wood after treatment to
thwart resurgent colonies.
Borates. Spray and foam applications of products
containing boron salts are applied to raw, uncoated wood
surfaces. Because penetration depths of borate solutions and
depth of drywood termite galleries vary, injection into existing
infestations should also be performed (see also wood injection
above and preventative treatments below).
Microwave. Microwave energy, applied to relatively
small sections of infested wood, kills termites by heating them.
Thermocouples should be inserted into treated members to insure
that adequate microwave energy is delivered. Microwave equipment
is not designed to treat areas where access is limited.
Electrocution. The probe of a hand-held "gun"
is passed slowly over the infested wood surface and inserted
directly into pellet "kick-out" holes. The high voltage
and low current energy emitted by the probe electrocutes termites
in the immediate application area. There is no way to measure a
lethal dose at a given location in wood with this device. In some
cases, holes must be drilled into wood and wires inserted to
Wood replacement. This method allows for absolute
removal of a drywood termite infestation if it is isolated to a
wood member which can be detached relatively easily, as for
example, a fascia board or a door. Make certain that there are no
galleries leading to adjacent wood members, otherwise, they will
also require treatment or removal.
Pre-construction. The most effective prevention for
drywood termites can be "built-in" to a home during its
construction phase. Pressure-treated lumber should be installed
wherever building codes allow. In the framing stage, all
untreated wood can be sprayed with borate solutions.
Post-construction. It is impossible to treat all wood
in a completed house with residual chemicals. Exposed, unfinished
wood can be sprayed with borates which repel swarming termites,
but keep in mind that untreated wood may still be susceptible to
infestation as the borate spray residue will not kill wandering
adults on contact. Wall voids and attics can also be sprayed or
dusted with various residual insecticides which kill swarming
adults in search of a nest site.
Because drywood termites are hidden inside the wood they infest, it may be difficult to immediately verify the success of a given treatment. A swarm within a few years of treatment suggests either that the treatment was unsuccessful, infested wood was brought in, or a hidden, untreated, infestation was present and must now be treated. Accumulation of pellets, especially in a cone-shaped pattern, is also a sign of active drywood termites. All pellets should be removed after a treatment to insure that colony activity has ceased. A retreatment is warranted if new pellets are observed. Pellets may continue to trickle from wood after successful control if the wood member is periodically subjected to vibrations or jarring such as a door or door frame.
REC Research Report FTL 97-1, March 1997