Structural Pest Control and Pesticides - Structural Pre-Construction Subterranean Termite Control

Pre-Construction Subterranean Termite Control

Subterranean termites are by far, the most common termites in North Carolina. Several subterranean species are native to North Carolina, but their biology and activity are essentially the same. The Formosan subterranean termite, an imported species, has recently been identified in a few locations in the state, but they are not widely distributed at this time. Termites "nest" in the soil and from there they can attack structures by building shelter tubes from the soil to the wood in structures. To control termites, it is almost always necessary to use pesticides. Pesticides used to control termites are called termiticides. Termiticides may be applied as liquids or baits. When applied as a liquid, the termiticide is injected into the soil or to wood members of a structure. When a bait system is used, the bait is placed in specially designed bait stations in the soil around the exterior perimeter of a structure. In this publication, we will discuss some of the options that homeowners' can use to better understand how a structure is treated for termites.

Soil Treatments of Structures

The best time to provide protection against termites is during the planning and construction phase of a structure. The major objective of subterranean termite control is to establish a chemical barrier between the soil, where termites live and the wood in the home. A thorough pre-construction treatment is needed to protect the structure from termites. Treating a structure for termite control requires specialized equipment that homeowners usually do not have on hand such as a 100-gallon tank, roller pump and auxiliary motor to deliver the insecticide from the tank, hoses, treating tools, etc. Therefore, it is not recommended homeowners' attempt to treat their homes for termite control.

Treatments of Soil Adjacent to Foundation Elements

A continuous termiticide barrier is established in the soil adjacent to foundation elements (in accordance with label directions). This treatment is usually performed after the footings have been poured and the foundation walls and /or pillars have been built. The termiticide is applied in the soil by trenching or trenching and rodding adjacent to foundation elements. With shallow footings, the soil is removed by trenching and is treated with the termiticide as it is replaced into the trench. Where footings are exposed, treatment is performed next to the footing but not below the bottom of the footing. Where deep footings exists, such as a basement home, termiticides are applied as the soil backfill is placed around the foundation. Alternatively, the pest control operator may trench and rod into the trench or trench along the foundation walls and around pillars and other foundation elements, at the rate prescribed from the top of the grade to a minimum depth of 4 feet. The termiticide must be applied on all sides of all foundation elements, including chimney bases, foundation walls, pilasters and pillars. Where drain tile, french drains, or other foundation drainage systems present a hazard of contamination outside the treatment zone, treatment must be performed in a manner that will not introduce the insecticide into the drainage system. The insecticide must be mixed with water as required by the pesticide label and applied to a minimum depth of 4 feet at the rate of 4 gallons per 10 linear feet, per foot of depth.
 

Treatment of Concrete Slabs

One of the most common types of construction in North Carolina is the concrete slab resting on the soil. Often a slab will crack or shrink away from the foundation wall allowing termites to infest the wood above. In addition, concrete slabs usually have many other points of entry such as bath traps, plumbing outlets, construction joints, etc. Treatment to these areas requires establishing a horizontal barrier. The soil underneath and around the concrete slab must be treated with the termiticide before the concrete slab is poured. The termiticide must be applied after installation of the sub-slab fill material. Diluted insecticide is then applied to the fill material at the rate of 1 gal. per 10-sq. ft. Where the final fill material is washed stone, termiticide is applied at the rate of 1½ gal. per 10 sq. ft. In addition to treatment underneath the slab, foundation elements are treated as stated above. In addition, a vertical barrier must be established around foundation elements adjacent to slabs. For information regarding vertical treatments, see the Treatments of Soil Adjacent to Foundation Elements section above.

Subterranean Termite Sub-Slab Treatment Release Form

The Sub Slab Release Form is used when concrete slabs are poured without treatment of the soil for the prevention of subterranean termites during its construction as required under minimum standards for the pre-treatment of structures. This document informs the property owner of areas of the property that were not treated for the prevention of subterranean termites during its construction and should only be signed by the property owner. Refer to the Sub Slab Release Form Memo for additional information.

Stages of Treatment

One of the most important aspects of performing a successful pre-construction termite treatment involves the close working relationship between the PCO and the builder. Several trips are usually necessary in order to perform the different stages of treatment. The different stages and timing of applications are as follows: 1. After footing approval and before pouring of footings. 2. After backfill of foundations in crawl space. 3. After leveling of all slab areas. 4. After (or during) backfill and final grading to the exterior. Although four trips to the property are shown here, a proper treatment can usually be performed in three trips through careful scheduling.

Bait/Monitoring Systems

Baits/monitoring systems may be used for pre-construction termite control. This system must be installed after the final grade and landscaping is completed. These systems are a recent innovation in termite control. Termiticide baits control termites by eliminating or reducing the size of the termite colony. They do not create a barrier around the structure, as do the liquid insecticides discussed earlier. Presently, termiticide baits are either insect growth regulators (IGRs) or slow acting poisons. The use of termiticide baits can significantly reduce or eliminate the need for a conventional liquid insecticide.

There are two strategies for the use of termiticide baits. One involves the placement of monitoring devices containing untreated wood or other cellulose material in the soil around the structure to be protected. When termites are detected in the monitoring device, the untreated cellulose material is replaced with a treated material, referred to as a "termiticide bait". The bait material is replenished as long as termites continue feeding. For the bait system to be effective, the proper number of stations must be installed and the stations must be inspected or monitored regularly as indicated on the product label. When termites stop feeding, the bait is replaced with untreated wood or other cellulose material. As a variation of this strategy, devices may be pre-baited and placed in the soil in areas where termites are present.

The second bait strategy currently in use involves the attachment of bait devices directly to the surface of construction elements where termites are actively feeding. These devices are pre-baited and are attached to the foundation walls, floor joists, sub-floor and other similar locations. Termites then feed on the bait material.

There are advantages and disadvantages to the use of termiticide baits. Baits may be used to treat structures that cannot be treated with liquid termiticides due to the presence of a well, inaccessibility of infested areas or concerns about the use of pesticides. However, in most cases, termiticide baits do not provide quick control of the termite infestation. In addition, the maintenance of bait system service agreements is normally more expensive than maintenance of conventional treatment warranties.

Conclusion

Remember the best method for the control of subterranean termites is prevention. Listed below are some options that should be used in termite control. Preventive measures should include:

• Removal of all stumps, roots, wood, and other cellulose materials from the building site before construction is begun.
• Removal of all form boards and grade stakes used in construction.
• There should be no contact between the building woodwork and the soil or fill material. Exterior woodwork should be located a minimum of 6 inches above ground and beams in crawl spaces at least 18 inches above ground to provide ample space to make future inspections.
• Ventilation openings in foundations should be designed to prevent dead air pockets. This helps keep the ground dry and unfavorable for termites.
• Thorough annual inspections should be conducted to discover evidence of termite activity such as shelter tubes on foundation surfaces, discarded wings or adult termites.
• Any wood that contacts the soil, such as fence posts and foundation elements should be made of pressure treated wood.
• Foundation areas should be made accessible for inspection if possible.
• Proper grading to direct water away form the structure

For questions or if additional assistance is required, please contact the NCDA&CS Structural Pest Control Section at 984-236-4625.       Directions 

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