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Water damages more homes that Termites.

Wood is a porous material and will absorb moisture from the air. Moisture is attracted to the walls of the tubes that make up the wood. As walls absorb moisture, the wood swells. If the humidity is kept at 100 percent, the walls become saturated with water. The moisture content at which this occurs is the fiber saturation point, which is approximately 30 percent by weight for most species used in construction. Fungi will only decay wood with a moisture content above the fiber saturation point. To allow a safety margin, wood with a moisture content above 20 percent is considered to be susceptible to decay.

Wood in properly constructed buildings seldom will have a moisture content above 16 to l8 percent. Thus, wood will only decay if it is in contact with the ground or wetted by an external source of moisture, such as rain seepage, plumbing leaks, or condensation. Dry wood will never decay. Also, the drier the wood, the less likely it is to be attacked by most types of wood-inhabiting insects.

Wood-inhabiting fungi are small plants that lack chlorophyll and use wood as their food source. Some fungi use only the starch and proteins in the wood and don't weaken it. Others use the structural components, and as they grow, they weaken the wood, which eventually becomes structurally useless. All fungi require moisture, oxygen, warmth, and food. The keys to preventing or controlling growth of fungi in wood in buildings are to either keep the wood dry (below a mois-ture content of 20 percent) or to use preservative-treated or naturally resistant heartwood or selected species.

Wood-inhabiting insects can be divided into those that use wood as a food materia -- termites and wood-boring beetles, for example -- and those that use it for shelter -- carpenter ants and bees, for example. Damage is caused by immature termites called nymphs, by the larvae or grubs of the wood-boring beetles, and by the adults in ants and bees.

Some wood-inhabiting organisms are found in all parts of the country, others are highly localized. Some, although common, cause very little structural damage. The following is a description of the major wood-inhabiting fungi and insects in the United States.

Surface molds and sapstain fungi

Surface molds or mildew fungi discolor the surface of wood, but do not weaken it. They are generally green, black, or orange and powdery in appearance. The various building codes allow the use of framing lumber with surface molds or mildew, providing that the wood is dry and not decayed. Spores (or seeds) of surface molds or mildew fungi grow quickly on moist wood or on wood in very humid conditions.

They can grow on wood before it is seasoned, when it is in the supplier's yard or on the building site, or in a finished house. When the wood dries, the fungi die or become dormant, but they do not change their appearance. Thus, wherever surface molds or mildew fungi are observed on wood in a building, it is a warning sign that at some time the wood was moist or humidity was high.

Surface molds and mildew fungi are controlled by eliminating the source of high humidity or excess moisture, for example by repairing leaks, improving ventilation in attics or crawl spaces, or installing soil covers. Before taking corrective action, the source of the moisture that allowed fungus growth must be determined. If the wood is dry and the sources of moisture are no longer present, no corrective action need be taken.

Sapstain or bluestain fungi are similar to surface molds, except that the discoloration goes deep into the wood. They color the wood blue, black, or gray and do not weaken it. They grow quickly on moist wood and do not change their appearance when they die or become dormant. They usually occur in the living tree or before the wood is seasoned, but sometimes they grow in the supplier's yard, on the building site, or in a finished house. In the latter case, they are normally associated with rain seepage or leaks. Stain fungi are a warning sign that at some time the wood was moist. Control is the same as for surface molds or mildew fungi.

Water-conducting fungi

Most decay fungi are able to grow only on moist wood and cannot attack adjacent dry wood. Two brown-rot fungi, Poria incrassata and Merulius lacrymans, are able to conduct water for several feet through root-like strands or rhizomorphs, to moisten wood and then to decay it.

These are sometimes called water-conducting or dry-rot fungi. They can decay wood in houses very rapidly, but fortunately they are quite rare. Poria incrassata is found most frequently in the Southeast and West. Merulius lacrymans occurs in the Northeast.

Both fungi can cause extensive damage in floors and walls away from obvious sources of moisture. Decayed wood has the characteristics of brown rotted wood except that the surface of the wood sometimes appears wavy but apparently sound, although the inte-rior may be heavily decayed. The rhizomorphs that characterize these fungi can be up to an inch in diameter and white to black in color, depending on their age. They can penetrate foundation walls and often are hidden between wood members.

The source of moisture supporting the fungal growth must be found and eliminated to control decay. Common sources include water leaks and wood in contact with or close to the soil: for example, next to earth-filled porches or planters. Where the fungus grows from a porch, the soil should be removed from the porch next to the foundation wall to prevent continued growth of the fungus into the house. Poria incrassata normally occurs in new or remodeled houses and can cause extensive damage within two to three years.

Brown-rot and white-rot fungi

The fungi often produce a whitish, cottony growth on the surface of wood. They grow only on moist wood. The fungi can be present in the wood when it is brought into the house or can grow from the spores that are always present in the air and soil. Wood attacked by these fungi should not be used in construction. Wood decayed by brown-rot fungi is brittle and darkened in color. As decay proceeds, the wood shrinks, twists, and cracks perpendicular to the grain. Finally, it becomes dry and powdery. Brown-rot is the commonest type of decay found in wood in houses.

Wood decayed by white-rot fungi is fibrous and spongy and is bleached in color. Sometimes it has thin, dark lines around decayed areas. The wood does not shrink until decay is advanced.

These fungi can be controlled by eliminating the source of moisture that allows them to grow, for example by improving drainage and ventilation under a house, repairing water leaks, or preventing water seepage. When the wood dries, the fungi die or become dormant. Spraying wood with chemicals does not control decay. If the moisture source cannot be eliminated, all the decayed wood should be replaced with pressure-treated wood.

White-pocket rot

White-pocket rot is caused by a fungus that attacks the heartwood of living trees. Decayed wood contains numerous small, spindle- shaped white pockets filled with fungus. These pockets are generally 3 to 13 mm long. When wood from infected trees is seasoned, the fungus dies. Therefore, no control is necessary. White-pocket rot generally is found in softwood lumber from the West Coast.

Carpenter ants

Carpenter AntsCarpenter ants burrow into wood to

make nests, but do not feed on the wood. They commonly nest in dead portions of standing trees, stumps, logs, and sometimes wood in houses. Normally they do not cause extensive structural damage. Most species start their nests in moist wood that has begun to decay. They attack both hardwoods and softwoods.

The most obvious sign of infestation is the large reddish-brown to black ants, 6 to 13 mm long, inside the house. Damage occurs in the interior of the wood. There may be piles or scattered bits of wood powder (frass), which are very fibrous and sawdust-like. If the frass is from decayed wood, pieces tend to be darker and more square ended. The frass is expelled from cracks and crevices, or from slit-like openings made in the wood by the ants. It is often found in basements, dark closets, attics, under porches, and in crawl spaces. Galleries in the wood extend along the grain and around the annual rings.

The softer springwood is removed first. The surfaces of the galleries are smooth, as if they had been sandpapered, and are clean. The most effective way to control carpenter ants is to locate the nest and kill the queen in colonies in and near the house with insecticides. It is sometimes also helpful to treat the voids in walls, etc. For current information on control, an entomologist should be contacted.

Wood-boring beetles, bees, and wasps

There are numerous species of wood-boring insects that occur in houses. Some of these cause considerable damage if not controlled quickly. Others are of minor importance and attack only unseasoned wood. Beetles, bees, and wasps all have larval, or grub, stages in their life cycles, and the mature flying insects produce entry or exit holes in the surface of the wood. These holes, and sawdust from tunnels behind the holes, are generally the first evidence of attack that is visible to the building inspector.

Correct identification of the insect responsible for the damage is essential if the appropriate control method is to be selected. The characteristics of each of the more common groups of beetles, bees, and wasps are discussed in the following table which summarizes the size and shape of entry or exit holes produced by wood-boring insects, the types of wood they attack, the appearance of frass or sawdust in insect tunnels, and the insect's ability to reinfest wood in a house.

To use the table, match the size and shape of the exit or entry holes in the wood to those listed in the table; note whether the damaged wood is a hardwood or softwood and whether damage is in a new or old wood product (evidence of inactive infestations of insects that attack only new wood will often be found in old wood; there is no need for control of these). Next, probe the wood to determine the appearance of the frass. It should then be possible to identify the insect type. It is clear from the table that there is often considerable variation within particular insect groups.

Where the inspector is unsure of the identity of the insect causing damage, a qualified entomologist should be consulted.

 

How to identify common beetles, bees and wasps that attack wood.

Shape and Size (inches) of Exit/ Entry Hole Wood Type Age
of Wood At- tacked
Appearance of Frass in Tunnels Insect Type Re- infest?
Round 1/50 - 1/8 Softwood & hardwood New None Present Ambrosia beetles No
Round 1/32 - 1/16 Hardwood New & old Fine, flour-like, loosely packed Lyctid beetles No
Round 1/16 - 3/32 Bark/ sapwood interface New Fine to coarse, bark colored, tightly packed Bark beetles No
Round 1/16 - 1/8 Softwood & hardwood New & old Fine powder and pellets, loosely packed; pellets may be absent and frass tightly packed in some hardwoods Anobiid beetles Yes
Round 3/32 - 9/32 Softwood & hardwood (bamboo) New Fine to coarse powder, tightly packed Bostrichid beetles Rarely
Round 1/6 - 1/4 Softwood New Coarse, tightly packed Horntail or woodwasp No
Round 1/2 Softwood New & old None Present Carpenter bee Yes
Round-oval 1/8 - 3/8 Softwood & hardwood New Coarse to fibrous, mostly absent Round- headed borer No
Oval 1/8 - 1/2 Softwood & hardwood New Sawdust-like, tightly packed Flat-headed borer No
Oval 1/4 - 3/8 Softwood New & old Very fine powder & tiny pellets, tight Old house borer Yes
Flat oval 1/2 or more or irregular surface groove 1/8 - 1/2 wide Softwood & hardwood New Absent or sawdust-like, coarse to fibrous; tightly packed Round- or flat-headed borer, wood machined after attack No

(New wood is defined as standing or freshly felled trees and unseasoned lumber. Old wood is seasoned or dried lumber.)

Lyctid powder-post beetles

Lyctids attack only the sapwood of hardwoods with large pores: for example, oak, hickory, ash, walnut, pecan, and many tropical hardwoods. They reinfest seasoned wood until it disintegrates. Lyctids range from 3 to 7 mm in length and are reddish-brown to black. The presence of small piles of fine flour-like wood powder (frass) on or under the wood is the most obvious sign of infestation.

Even a slight jarring of the wood makes the frass sift from the holes. There are no pellets. The exit holes are round and vary from 1 to 1.5 mm in diameter. Most of the tunnels are about 1.5 mm in diameter and loosely packed with fine frass. If damage is severe, the sapwood may be completely converted to frass within a few years and held in only by a very thin veneer of surface wood with beetle exit holes.

The amount of damage depends on the level of starch in the wood. Infestations are normally limited to hardwood paneling, trim, furniture, and flooring. Replacement or removal and fumigation of infested materials are usually the most economical and effective control methods. For current information on the use of residual insecticides, the inspector should contact the extension entomologist at his nearest land grant university or a reputable pest control company.

Anobiid beetles

The most common anobiids attack the sapwood of hardwoods and softwoods. They reinfest seasoned wood if environmental conditions are favorable. Attacks often start in poorly heated or ventilated crawl spaces and spread to other parts of the house. They rarely occur in houses on slab foundations. Anobiids range from 3 to 7 mm in length and are reddish-brown to nearly black.

Adult insects are rarely seen. The most obvious sign of infestation is the accumulation of powdery frass and tiny pellets underneath infested wood or streaming from exit holes. The exit holes are round and vary from 1.5 to 3 mm in diameter. If there are large numbers of holes and the powder is bright and light colored like freshly sawed wood, the infestation is both old and active. If all the frass is yellowed and partially caked on the surface where it lies, the infestation has been controlled or has died out naturally. Anobiid tunnels are normally loosely packed with frass and pellets. It is normally 10 or more years before the number of beetles infesting wood becomes large enough for their presence to be noted. Control can be achieved by both chemical and non-chemical methods. For current information on control of anobiids, the inspector should contact the extension entomologist at his nearest land grant university or a reputable pest control company.

Bostrichid powderpost beetles

Most bostrichids attack hardwoods, but a few species attack softwoods. They rarely attack and reinfest seasoned wood. Bostrichids range from 2.5 to 7 mm in length and from reddish-brown to black. The black polycaon is an atypical bostrichid and can be 13 to 25 mm in length. The first signs of infestation are circular entry holes for the egg tunnels made by the females. The exit holes made by adults are similar, but are usually filled with frass. The frass is meal-like and contains no pellets. It is tightly packed in the tunnels and does not sift out of the wood easily. The exit holes are round and vary from 2.5 to 9 mm in diameter. Bostrichid tunnels are round and range from 1.5 to 10 mm in diameter.

If damage is extreme, the sapwood may be completely consumed. Bostrichids rarely cause significant damage in framing lumber and primarily affect individual pieces of hardwood flooring or trim. Replacement of structurally weakened members is usually the most economical and effective control method.

Old house borer

                                                  An Old-House borer

This beetle infests the sapwood of softwoods, primarily pine. It reinfests seasoned wood, unless it is very dry.

The old house borer probably ranks next to termites in the frequency with which it occurs in houses in the mid-Atlantic states. The beetle ranges from 15 to 25 mm in length, and is brownish-black in color. The first noticeable sign of infestation by the old house borer may be the sound of larvae boring in the wood. They make a rhythmic ticking or rasping sound, much like a mouse gnawing. In severe infestations the frass, which is packed loosely in tunnels, may cause the thin surface layer of the wood to bulge out, giving the wood a blistered look.

When adults emerge (three to five years in the South, five to seven years in the North), small piles of frass may appear beneath or on top of infested wood. The exit holes are oval and 6 to 10 mm in diameter. They may be made through hardwood, plywood, wood siding, trim, sheetrock, paneling, or flooring. The frass is composed of very fine powder and tiny blunt-ended pellets.

If damage is extreme, the sapwood may be completely reduced to powdery frass with a very thin layer of surface wood. The surfaces of the tunnels have a characteristic rippled pattern, like sand over which water has washed. Control can be achieved by both chemical and non-chemical methods. For current information on control of the old house borer, the inspector should contact the extension entomologist at his nearest land grant university or a reputable pest control company.

Carpenter bees

Carpenter bees usually attack soft and easy-to-work woods, such as California redwood, cypress, cedar, and Douglas fir. Bare wood, such as unfinished siding or roof trim, is preferred. The only external evidence of attack is the entry holes made by the female. These are round and 9 mm in diameter. A rather course sawdust-like frass may accumulate on surfaces below the entry hole. The frass is usually the color of freshly sawed wood.

The presence of carpenter bees in wood sometimes attracts woodpeckers, which increases the damage to the surface of the wood. The carpenter bee tunnels turn at a right angle after extending approximately an inch across the grain of the wood, except when entry is through the end of a board. They then follow the grain of the wood in a straight line, sometimes for several feet.

The tunnels are smooth-walled. It takes several years of neglect for serious structural failure to occur. However, damaged wood is very unsightly, particularly if woodpeckers have followed the bees. The bees can be controlled by applying five to 10 percent carbaryl (Sevin) dust into the entry holes. Several days after treatment, the holes should be plugged with dowel or plastic wood. Prevention is best achieved by painting all exposed wood surfaces.

Other wood-inhabiting insects

There are several other species of insects that infest dying or freshly felled trees or unseasoned wood, but that do not reinfest seasoned wood. They may emerge from wood in a finished house or evidence of their presence may be observed. On rare occasions, control measures may be justified to prevent disfigurement of wood, but control is not needed to prevent structural weakening.

  • Ambrosia beetles. These insects attack unseasoned sapwood and heartwood of soft-wood and hardwood logs, producing circular bore holes 0.5 to 3 mm in diameter. Bore holes do not contain frass, but are frequently stained blue, black, or brown. The insects do not infest seasoned wood.
  • Bark beetles. These beetles tunnel at the wood/bark interface and etch the surface of wood immediately below the bark. Beetles left under bark edges on lumber may survive for a year or more as the wood dries. Some brown, gritty frass may fall from circular bore holes 1.5 to 2.5 mm in diameter in the bark. These insects do not infest wood.
  • Horntails (wood wasps). Horntails generally attack unseasoned softwoods and do not reinfest seasoned wood. One species sometimes emerges in houses from hardwood firewood. Horntails occa-sionally emerge through panel-ing, siding, or sheetrock in new houses; it may take four to five years for them to emerge. They attack both sapwood and heartwood, producing a tunnel that is roughly C-shaped in the tree. Exit holes and tunnels are circular in cross-section and 1.5 to 7 mm in diameter. Tunnels are tightly packed with course frass. Frequently, tunnels are exposed on the surface of lumber by milling after the development of the insect.
  • Round-headed borers. Several species are included in this group. They attack the sapwood of softwoods and hardwoods during storage, but rarely attack seasoned wood. The old house borer is the major round-headed borer that can reinfest seasoned wood. When round-headed borers emerge from wood, they make slightly oval to nearly round exit holes 3 to 10 mm in diameter. Frass varies from rather fine and meal-like in some species to very course fibers like pipe tobacco in others. Frass may be absent from tun-nels, particularly where the wood was machined after the emergence of the insects.
  • Flat-headed borers. These borers attack sapwood and heartwood of softwoods and hardwoods. Exit holes are oval, with the long diameter 3 to 13 mm. Wood damaged by flat-headed borers is generally sawed after damage has occurred, so tunnels are exposed on the surface of infested wood. Tunnels are packed with sawdust-like borings and pellets, and tunnel walls are covered with fine transverse lines somewhat similar to some round-headed borers. However, the tunnels are much more flattened. The golden buprestid is one species of flat-headed borer that occurs occasionally in the Rocky Mountain and Pacific Coast states. It produces an oval exit hole 5 to 7 mm across, and may not emerge from wood in houses for 10 or more years after infestation of the wood. It does not reinfest seasoned wood.

If signs of insect or fungus damage other than those already described are observed, the inspector should have the organism responsible identified before recommending corrective measures.

Small samples of damaged wood, with any frass and insect specimens (larvae or grubs must be stored in vials filled with alcohol), should be sent for identification to the entomology or pathology department of the state land grant university.

Editor's Note: This material is excerpted from A Guide to the Inspection of Existing Homes for Wood Inhabiting Insects, written by Michael P. Levy and published by the U.S. Department of Housing and Urban Development HUD.

 

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