White rot fungi are more prevalent on hard¬woods, although they are also present in many conifer species. In the advanced stage of decay, white-rot fungi bleach or whiten wood or they form small degraded white pockets in the wood.
Brown and white rot fungi tend to be inside the pole where moisture conditions are more stable. They are often associated with deep checks that penetrated past the original treat¬ment zone. While their damage is important, they can generally be controlled by the application of volatile or water diffusible treatments. The end result of internal decay is a shell of treatment surrounding a hollow core. The thickness of that original treatment can determine whether an internally decayed pole is salvageable.
Soft rot fungi attack the surfaces of both hardwoods and conifers, particularly where pre-servative levels have declined below their initial treatment levels through leaching. Soft-rot fungi slowly cause external softening of treated wood, resulting in extensive damage below ground. Soft rot fungi are most prevalent on southern pine poles, although they are also common on poles of Douglas-fir that have been treated with pentachlorophenol in either methylene chloride or liquefied petroleum gas. Although neither of these treatments is currently used, many poles treated with these systems remain in service. Soft rot fungi are especially important because they reduce the effective pole circumference, producing very sharp declines in flexural prop¬erties. Many of these fungi are also tolerant of preservatives, allowing them to attack wood that may have lost some, but not all of its original treatment.
Non-decay Fungi
Numerous non-decay fungi also inhabit wood; they feed on cell contents, certain components of cell walls, and the products of decay. Frequently, only non-decay fungi can be isolated from rotten wood because the decay fungi, having run out of food, have died. Sapwood-staining fungi may reduce the toughness of severely discolored wood; other non-decay fungi gradually detoxify preservatives, preparing the way for decay fungi. Some rapidly growing non-decay fungi may inter¬fere with efforts to culture the slower growing decay fungi from wood. The interaction of fungi, both decay and non-decay types, and their roles in the decay process are still to be defined.
Insects
Wood in or above ground may be attacked by ter¬mites, carpenter ants, or beetles. Termites work within and use wood as a food source; there is virtually no external evidence of their presence until winged adults emerge and swarm in late summer and early fall. These social insects have a well organized colony structure with a queen, workers and soldiers. Workers feed nearly con¬tinuously and a large colony can approach one
million workers. Collections of wings outside the nest in checks or other collection areas, discarded by reproductives (alates) as they mate to start new colonies, may be the first indicator of termite presence. Some species also produce mud tubes up the pole surface or inside checks that indicate the presence of an infestation. Although their lengths vary from 1/4 inch or less (subterranean and drywood) to 3/4 inch (dampwood), termites have bodies of fairly uniform width; the reproduc¬tives have wings of equal length (Figure 19).
Subterranean termites are wide-spread and cause extensive damage, especially in southern states but they are also present in drier parts of the country. Sure signs of their presence are the mud tunnels that the termite workers build from their nests in the ground up across treated wood or concrete to non-treated wood above. Subterranean termites are distributed between 50° N and 50° S latitude although there may be
isolated occurrences north of this zone. Global changes in climate are likely to extend this range.
In warmer portions of the country, wood may also be subject to very aggressive attack by an introduced species, the Formosan termite (Coptotermes formosanus). This subterranean termite has large colonies with as many as 6 to 7 million workers. Fortunately, this species is cur¬rently only found in Hawaii, along the Gulf Coast and in extreme southern California. The presence of this termite in Hawaii, however, has resulted in a requirement that all wood used in houses be preservative protected.
Dampwood termites (Zootermopsis augus¬ticollis) inhabit moist wood in, on, or above the ground along the Pacific Coast. The workers of this species are very large and easily identified, while the soldiers have extremely large pincers. This species can be a problem in poles, but it is most often associated with very deep wide checks or prior woodpecker attack. In both cases, the openings allow moisture to enter, creating ideal conditions for attack. Dampwood termites
appear to be very susceptible to preservative treatments.
Drywood termites feed on dry wood, primar¬ily in the southern United States and the Pacific Southwest. These species can live in wood at 12% MC, and the only evidence of their presence is the frass or insect droppings that they periodically expel from their colonies. (Figure 20). Drywood termites can invade poles and crossarms, where their presence is difficult and expensive to detect. The best preventative method is a well-treated preservative shell.
The initial treatments currently used for poles are all capable of preventing termite attack, but checks or other damage to the wood can create non-treated zones where termites can invade. Termites are best controlled by producing a well-treated pole without deep checks that penetrate beyond the treated shell.
Carpenter ants are also social insects with a queen and major or minor workers (Figure 21). The ants have a restricted waist, and the reproductives have wings of unequal length. The dark-colored ants grow as long as 3/4 inch. Unlike termites, which eat wood, ants hollow out wood only for shelter, forming piles of “sawdust” at the base of poles, which attest to their presence in the wood Figure 22). Ants must leave the nest to find food and are frequently seen scurrying around poles particularly at night (they are noc¬turnal). They are difficult to control because they do not eat the wood. They also tend to have a main nest along with satellite nests. This makes it
Figure 21. In contrast to termites, carpenter ants (Camponotus sp.) have restricted waists and reproductives have shorter wings of unequal length (photo credit: Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org