How to Prevent Insect Damage to Wood Structures

The most effective method of insect control is prevention.The cost of repairing damage in structures is usually substantial. Most damage is caused by termites and powder-post beetles. Subterranean termites live in the soil, and must maintain contact with it. Found in most states, they are the most important wood products insect, and are most destructive in the South. The key to subterranean termite control lies in construction practices. Their activity can be discouraged by the following: proper grading to keep moisture from the building, elimination of wood scraps-stumps from the site, proper ventilation of crawl spaces, keeping exterior wood 6 inches from the soil, keeping wood in crawl spaces 18 inches from the soil, keeping foundations impervious to termites–even a 1/64-inch crack allows entry–, and use of termite shields. Despite all these precautions termites may gain entry. Wood on, in, or near the ground must be treated. Load bearing timbers and other wood near the soil susceptible to decay or termites should preferably be pressure treated. Insecticides applied to the soil at rates of 1 and 2 gallons per 10 sq.ft. depending on soil, locations, and construction have been very effective. Benzene hexachloride, 0.8 percent gamma isomer, lindane, 0.8 percent, chlordane, 1.0 percent; and dieldrin, 0.5 percent in water emulsion or oil are commonly used. DDT, 8 percent in oil, and sodium arsenite, 10 percent in water, are good but the latter is highly toxic. Drywood or dampwood termites are found in tropic or semi-tropic locations. Treating of all wood in a structure is desirable where the incidence of dry-wood termites is high. Insecticides applied by brush, dip, or soaking treatment also aid in preventing drywood termite attack. Dip or soak treating was more effective over a 4- year period. Brush coats giving complete protection were 5 percent pentachlorophenol in trichlorobenzene and 5 percent DDT plus 2 percent chlordane. Surface treatments applied as 5 minute to 4 hour soaks of the following insecticides gave complete protection: straight trichlorobenzene, chlordane 2 percent plus DDT 5 percent in trichlorobenzene-kerosene, pentachlorophenol 5 percent metallic copper. Powder post beetles are less destructive than termites, but are more complex and difficult to control. Lyctus, anobiid, and long-horn beetles are the most common types. Preventive measures include a 10 second dip of green lumber in 5 percent DDT or 0.5 percent gamma BHC cold water emulsion (for Lyctus beetles). Good sanitation in warehouses will prevent attack of seasoned lumber. Wood preservatives are not generally necessary, but may be used. Three minute dips of 5 percent DDT, 5 percent toxaphene, 2 percent chlordane, and 0.5 percent lindane have given excellent protection against severe Lyctus exposure for more than 5 years.

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