Fungus Problems for Southern Pines

Four groups of fungi infect southern pines without a specific choice of species: needle blights, heartrots, butt rots, and pitch cankers. (Fungi, bearing scientific binomials, cause diseases; they are not diseases. Diseases have common names.) Needle blights, like those caused by Hypoderma lethale, attack pines from seedlings to maturity. Needles of most species are infected with spring inoculations of spores that have lain dormant since their dissemination the previous summer. Lophodermium pinastri, also spread by airborne spores in wet weather, forms a black elongated growth on needles. Foliage then suddenly dies, and the malady is sometimes mistaken for seasonal shedding of needles.

Heartrot fungi, represented by many species of several genera, are the cause of the greatest volume loss of all diseases to standing timber. Some produce fungi fruiting bodies on trees lying on the ground, the spores spreading to infect and introduce decay to living stems. Conks of heartrots, often appearing like shelves or dark-colored elephant ears protruding from wounds or long-since-healed-over scars, are the fruiting bodies of some species. From these conks, spores disperse to infect other trees over many years. Conks knocked off diseased trees by wind or man disseminate

Figure 2.8 Texas leaf-cutting ant colony. With backhoe excavation, the top of a cavity was located 9 feet below the surface of the ground and extended diagonally farther downward. In winter, the gardens, into which the ants carry parts of needles, are especially deep, thus providing protection from the cold of the ground surface. (Texas Forest Service photo by Ron Billings)

Figure 2.8 Texas leaf-cutting ant colony. With backhoe excavation, the top of a cavity was located 9 feet below the surface of the ground and extended diagonally farther downward. In winter, the gardens, into which the ants carry parts of needles, are especially deep, thus providing protection from the cold of the ground surface. (Texas Forest Service photo by Ron Billings)

spores for as long as five years while the fruiting bodies lie on the ground. For the most important species, Fomes pini, spores are cast in spring and fall, when warm weather follows cool spells. Mycelia, the microscopic strands of the vegetative organ of the fungus, grow year round, introducing decay-causing toxic chemicals as they penetrate the interior of the tree.

Red heartrot is usually found only in southern pines over 50 years of age. Twenty-five percent of such older trees might be infected, thereby providing abundant habitat for housing the red cockaded woodpecker. As the heartwood deteriorates in circular fashion, the disease also bears the name red ring rot. Because many diseased stems do not exhibit fresh pitch flow from branch stubs and fire wounds, the lack of exuding sap may not reliably indicate the absence of the decay within the bole.

Most notable among the causal agents of butt rot fungi is Polyporus schweinitzii. Infection results in decay of the interior of a tree at its base, the rotting wood breaking into brown cubes. Seldom does the decay rise more than a few feet above the ground. The inconspicuous fruiting bodies may be found in the soil litter, still attached to the base of the tree.

When sap flows copiously from trees, and no insects are apparent, the cause likely is attributed to Fusarium lateritium, the fungus that causes pitch canker. Bark is retained, although the canker appears sunken and the wood beneath soaked with pitch. Fire danger is high in young stands in which wads of flammable gum collect on the trees.7

Cronartium fusiforme causes spindle-shaped cankers on branches, main stems, and the bases of needles. The alternate hosts of this fusiform rust are oak trees. Except around nurseries, elimination of oak trees is economically impractical. The disease may be spread by insects. Of particular significance in times of concern for sanitary landfills and other distressed planting sites is the effect of mycorrhizae fungi on the growth of pine seedlings. Mycorrhizae secrete a plant growth regulator—as well as enabling the transfer of nutrients from the soil to roots—which ordinarily enhances tree growth. However, the usefulness of such fungi is affected by methane gas given off by decomposing garbage in landfills. The gas may be phytotoxic, reducing root development and subsequent growth of seedlings. Inoculation with an auxin may compensate for the detrimental methane.8

Considerable concern has been expressed over the effect of ozone and nitrous oxide in the atmosphere upon the growth and survival of trees. Growth reduction of naturally regenerated southern pines over a 10-year period has been attributed by some observers to these industrial and vehicular contributions to the atmosphere. Reduction ranged from 10 to 31 percent for trees with initial diameters of one inch or more. Cause of diminished growth for this 1972-1982 period, however, was not totally identifiable. The period may have been normal, the previous decade's growth abnormally high. Ozone, however, is seen as responsible for some growth reduction in all major forest ecosystems, the decline continuing even if emissions into the atmosphere remain constant.9

High concentrations of ozone (O3) seem to have little effect on needle production, although foliage retention is often greater, according to trials in air-filtered chambers. Southern pines are considered intermediate in terms of suspected growth losses due to air pollution, in contrast to high-elevation spruce and fir.10

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