Monday, October 24, 2011
Low Impact Termite Management
In the United States there are four groups of termites of concern: subterranean (including the Formosan termite), drywood, dampwood and powderpost. Subterranean termites and drywood termites are the two general types. Subterranean termites "nest" in the soil and from there they can attack structures by building shelter tubes from the soil to the wood in structures. Subterranean termites cause more of the damage to homes and structures than drywood termites so will be my primary focus here. Termites will attack any material with cellulose, including wood, paper coated wall board, and paper (as in that treasured book collection that occupies the lower level of my home). Wood that is at least 30% water saturated provides enough moisture. Additionally, termites will find free-standing water such as condensation, rain or plumbing leaks and use this moisture as their main source for survival. Termites have been a part of the ecosystem for thousands of years and aid in the decomposition of wood, freeing the nutrients in the decaying material for reuse by other organisms. Termites rely on eating the cellulose found in wooden structures, furniture, stored food and paper. It is virtually impossible to reside anywhere in the United States without confronting termites at one point or another.
Subterranean termites are the common termite in most states, and live below ground in colonies. Mature termite colonies tend to be decentralized with numerous nesting and feeding locations, interconnected by underground tunnels. The size of a colony can vary from less than 10,000 termites occupying 100-200 square feet to millions of termites covering an area as large as a half an acre. In higher density residential areas, the colony or colonies responsible for damage may actually be located in a neighbor's yard, rather than beneath the house that is infested. This requires that termite treatment involve both in house treatment and creating an external perimeter control to push back the colony. One of the oldest and least toxic treatment of in house termites and other pests is boric acid which will shut down the termite's nervous system. The termite will go into "shock" and the boric acid will simultaneously dehydrate the termite.
The treatment options for termites are bating for control of the perimeter with spot treatment both inside and out and traditional chemical barriers. Physical barriers installed during construction are also possible. As a practical matter physical barriers cannot be effectively retrofitted. Prevention of termites should be part of the construction process. Building codes require in most locations require that a construction site be pretreated for termites. Proper construction techniques, such as isolating wood from the soil, elimination and prevention of moisture and the use of physical barriers such as crushed glass, basalt, granite, quartz or silica sand can prevent termite attack. Certainly, adoption of vigilant construction methods and the use of inert physical barriers can prevent termite penetration into the structure and can provide more permanent termite control than is possible with insecticide applications to the soil alone. Very few of us build our own homes and the inclusion of permanent physical termite barriers often does not make the list of desirable features.
The new technologies for termite control can be safer to use and potentially less harmful to the environment than relying only on pesticides alone. Termite baits use small amounts of insecticide to knock out populations of termites foraging in and around the structure. Some baits may even eradicate entire termite colonies. Various methods of termite baiting are used in various products. The Sentricon Colony Elimination System is a termite control system from Dow AgroSciences it is the oldest and most widely tested of the commercially available baiting systems. It is comprised of several slotted, sub-ground level cylinders containing wooden monitoring devices. When termite activity is detected in a particular unit, the monitoring insert is replaced with a special bait tube. The bait used is a chitin inhibiting chemical which prevents the termites from molting. The idea behind this baiting method is that foraging termites consume the bait and pass it along to others within the colony, eventually working its way up to the queen, thereby eliminating the colony.
Sentricon has been commercially available since 1996. Several university etymology departments have conducted field tests over the years in the termite hot spots of Hawaii and the southeast. Beginning in fall 1993, field studies were conducted with a prototype Sentricon system around three representative structures in Hawaii, each of which had a history of subterranean termite infestation and recurring problems. Application of the hexaflumuron baits which is the active ingredient in the Sentricon system eliminated all termite activity at these sites. Continued monitoring is very important, though. Several years later, termites were again found to be reinvading two of the locations, but using baits again eliminated the infestation. The University of Kentucky also performed independent research studies. They, too, found that the Sentricon® is an effective termite control option. Some of these studies involved structural that could not be controlled using conventional liquid methods, which require the application of hundreds of gallons of chemicals into the ground to create an unbroken wall of soil soaked with chemical.
The Sentricon Termite Colony Elimination System was developed by Dow AgroSciences (Indianapolis, IN), and is sold only through authorized pest control firms. Termite control is not a DIY project. The bait contains a slow-acting ingredient, hexaflumuron that works by stopping the insect’s growth. It interferes with chitin synthesis, which termites need to form a new exoskeleton. Hexaflumuron has low toxicity and low mobility in the soil. It binds strongly to soil particles and is not highly soluble in water. It is not likely to contaminate surface or groundwater and is used in bating systems in very small quantities so is not likely to come in contact with residents. Termite control with the Sentricon System ® entails a 3-step process: (1) initial monitoring to pinpoint termite activity, (2) delivery of the bait, and (3) subsequent monitoring to provide ongoing protection of the structure.
The Sentricon baiting systems is the most extensively tested baiting system. (For other systems see University of Kentucky review of baiting systems.) It can be used as a preventive method for subterranean termites and a remedial control tool for existing infestations in structures. However, it could take from one month to more than a year to control an ongoing infestation and is in my opinion best used to prevent infestation. One of the biggest challenges in baiting is getting termites to find the baits in the first place. The timetable for discovery will vary from property to property, depending on such factors as termite foraging intensity, time of year, moisture, and food availability. On one infested property in Kentucky, more than a dozen monitoring devices were "hit" (attacked) by termites within two weeks of installation; on another home in the same neighborhood, no below-ground stations were attacked during a full year of intensive monitoring despite two concurrent termite swarms inside the home. Similar variances in bait detection by termites (and thus effectiveness of the baiting system to treat and eliminate an ongoing infestation) have been reported elsewhere in the country.
Thus, baiting can take more than a year to push back an infestation and baiting is expensive. While the initial cost of baiting is much less than the initial treatment with a chemical barrier. A typical "barrier" treatment may involve hundreds of gallons of pesticide injected into the ground alongside the foundation, beneath concrete slabs, and within foundation walls and may require the drilling of concrete floors, walkways and driveways. The total cost for this initial treatment can be up to $2,500 for a suburban home, but the maintenance contact is $100-$200.
Termite control with baiting entails a 3-step process: (1) initial monitoring to pinpoint termite activity, (2) delivery of the bait, and (3) subsequent monitoring to provide ongoing protection of the structure. Monitoring stations are installed around the perimeter of the house 10- to 20- feet apart. Stations are typically installed one to two feet from the foundation, to avoid soil that may have been treated earlier with a liquid termiticide. Patios, driveways, and other paved surfaces are not stations can be installed farther out from the foundation, in adjoining plant beds, etc. Additional stations are installed in suspected termite foraging areas, such as near pre-existing termite damage, stumps, woodpiles, or moist areas on the property.
Bimonthly thereafter the bait stations are inspected for termite presence. When termites are found in a monitoring station, the untreated wood is replaced with a perforated plastic tube containing bait laced with a slow-acting termite growth inhibitor (hexaflumuron) and the termites feeding on the wood pieces are carefully dislodged and placed within the bait tube. Eventually, these termites tunnel through and out of the perforated tube, carrying the bait back to the colony. After termites are no longer found in the bait tubes, the baits are once again replaced with untreated wood pieces and monitoring continues. Even if the termite colony threatening the structure has been eliminated, reinfestation can occur and homes protected with bait systems will need to be continually inspected, monitored and maintained to guard against reinvasion from new colonies or previously suppressed ones. Once the termite population has been eliminated, the pest control firm will continue to monitor at three- to four-month intervals for an indefinite period so that the annual contract cost is substantial and may be up to $350-$800 per year, though the initial cost would typically be in the same range.