Part 4

The balsam woolly aphid was introduced into northeastern North America from Europe around the turn of the century. Since then it has become a pest of major importance to true firs on the east and west coasts of the continent, and threatens some 60,000 acres of Fraser fir in the southern Appalachians. Usually the balsam woolly aphid has two generations per year in the southern Appalachians. Eggs of the first generation hatch in late June and July followed by the second generation in September and October. The immature stage of the aphid known as a “crawler” is the only motile stage in the aphid’s life cycle. Once the crawler begins feeding, it transforms into an adult and never again moves. Reproduction is parthenogenic with each female laying approximately 100 eggs during her lifetime.

In the feeding process the aphid injects a salivary substance into the host tree, which causes growth abnormalities. Initial symptoms of aphid attack may include “gouting” of buds or twig nodes and some twig and branch die-back. Heavy stem attacks reduce the tree’s ability to translocate food and water. Usually a heavily infested tree dies within two to seven years.

Chemical control is effective but extremely costly and thus limited to very high-value areas along scenic road-ways. Other control measures include removal and destruction of infested material.

DISEASES

NEEDLE CAST

Needle cast is a very common disease of conifers throughout eastern and southern United States. Eastern white, loblolly, longleaf, pitch, pond, shortleaf, table mountain, and Virginia pines are all susceptible. _Hypoderma lethale_ is probably the most common cause of needle cast on the above hosts, with the exception of longleaf pine. _Lophodermium pinastri_ is also associated with needle cast.

Current pine needles are infected in the early summer, and by winter or early spring begin to turn brown at the tips. At this time the tree usually has a scorched appearance. Later, the browning progresses down the needle and the fungal fruiting bodies are produced. These are small, black, elongated structures known as hysterothecia, which open along a slit during moist weather to release their spores. The infected needles are often “cast,” leaving only the new growth, and causing the tree to have a tufted appearance.

Controls are seldom needed for this disease in forest stands. Infected trees usually recover and put out new foliage the year following heavy attacks. Nurseries or plantations should not be established in areas where needle cast is prevalent.

BROWN SPOT NEEDLE BLIGHT

Brown spot or brown spot needle blight is caused by the fungus _Scirrhia acicola_. Brown spot occurs in all the coastal states from Virginia to Texas, and inland to Arkansas and Tennessee. All southern pines are attacked by the fungus, but only longleaf pine seedlings are seriously damaged.

Initial infection of pine needles results in the development of small, circular spots of grey green color, which later turn brown. As the fungus continues to grow, a necrotic area encircles the needle, appearing as a brown band. The infected area will then increase in size, eventually resulting in the death of the needle. Fruiting bodies, called acervuli, develop in the dead areas of the needle. Spores are extruded from the acervuli in a water soluble gelatinuous matrix throughout the entire year. The spores are washed apart and splashed short distances by rain drops. These spores spread the disease from seedling to seedling. During the winter and early spring, the sexual stage of the fungus is produced on dead needles. Ascospores, produced in a fruiting body called a perithecium, are light and wind-disseminated. These spores are responsible for disease spread. During the grass stage, seedlings often become heavily infected by the brown spot fungus, resulting in partial to complete defoliation. Seedlings which are nearly defoliated every year remain in the grass stage and eventually die. Three successive years of complete defoliation will result in death. The disease is very damaging during wet years, especially in areas where the fungus has become well established in the absence of controls.

The disease can be reduced by control burning during the winter months. On seedlings, fire burns the diseased needles and reduces the amount of available inoculum for reinfection, leaving the large terminal bud unharmed. Often a single prescribed burn reduces the disease intensity to such low levels that vigorous seedling height growth begins the following year. Fungicide sprays will also reduce brown spot on high valued trees.

PINE NEEDLE RUST

Nearly all the native pines in southern United States are attacked by various needle rust fungi of the genus _Coleosporium_. This disease is very common, but causes little harm to the trees. Many species of this rust also attack broadleaved weeds in addition to the pines, needing both host types to complete their life cycle.

Needle rusts are most prevalent on young trees in the seedling to sapling stage. In the spring or early summer small, delicate white fungus “cups” filled with yellow to orange spores are produced on the needles. From a distance entire seedlings may appear to have a whitish or yellowish cast. Individual needles which are heavily infected may die, turn brown, and drop from the tree. However, the entire tree is rarely defoliated. Small red “rust pustules” form on the undersurface of the weed leaves. These are replaced by dark structures later in the summer.

The needle rusts are not important enough to warrant control in natural forests or plantations. If the weed (alternate) host is known, it can be eradicated around nurseries of susceptible pine species. However, it would be better to establish nurseries in rust free areas.

CEDAR APPLE RUST

Cedar apple rust, caused by _Gymnosporangium juniperi-virginianae_, is important commercially in the apple-growing regions of the Virginias, Carolinas, and the Mississippi Valley. The alternate hosts of this rust are eastern red cedar and several species of junipers.

Cedar “apples” or galls are the characteristic signs of the fungus on cedars. Cedar needles are infected in the summer by wind-borne spores from apple leaves. By the next spring or early summer galls begin to appear as small greenish brown swellings on the upper needle surfaces. By fall, the infected needle turns into a chocolate brown gall covered with small circular depressions. The following spring, orange jelly-like tendrils protrude from the galls producing an attractive ornament for the cedar tree. Spores produced from these orange spore masses are then capable of reinfecting apple leaves, thus completing the fungus life cycle.

No practical control of the rust on cedars is available because of the low value of cedar. However, considerable effort is expended to protect apple trees. Where apple is to be protected, cedars should be eliminated in the vicinity or, rust galls should be picked or cut off cedars before the galls mature.

CEDAR BLIGHT

Cedar blight, caused by _Phomopsis juniperovora_, is most severe on eastern red and Rocky Mountain cedars. Other hosts include arborvitae, cypress, and Atlantic white cedar. The disease ranges from the mid-West to the Atlantic coast and south to Alabama where it is most common in nurseries.

Symptoms on red cedar resemble that of drought. The tips of branches are killed back and sometimes entire trees will turn brown. The fungus forms black fruiting bodies on needles and stem lesions. Fungus spores are distributed by rainwater; nursery overhead sprinkling systems also facilitate blight spread.

Control of cedar blight is initiated by removing and burning infected nursery stock early in the season before infection becomes heavy. Seedbeds should be well drained. Avoid introducing cedar stock to an infected nursery. The location of cedars in the nursery should be changed frequently and, where possible, cedar beds should be kept well away from older cedar or cedar hedges. Seedlings growing in low-density seed beds are more vulnerable to the blight; thus beds should be fully stocked. Cedar mulch should never be used on cedar beds. Avoid wounding nursery transplants. No economically feasible control is available for forest stands.

FUSIFORM RUST

Fusiform rust, caused by _Cronartium fusiforme_, is one of the most important diseases on southern pines. This rust is found from Maryland to Florida and west to Texas and southern Arkansas. The rust’s most important impact is in nurseries, seed orchards, and young plantations. Loblolly and slash pines are very susceptible to this rust. Pitch and pond pines are moderately susceptible, longleaf pine is fairly resistant, and shortleaf pine is highly resistant.

The most easily recognized symptom is the spindle-shaped canker on the pine branches or main stem. In early spring these swellings appear yellow to orange as the fungus produces powdery spores. As host tissue is killed, older stem cankers may become flat or sunken. Cankers often girdle trees and wind breakage at the canker is common. Fungus spores from the pine infect oak leaves. Brown hair-like structures, produced on the underside of the leaves in late spring, are the most conspicuous signs. These projections produce spores which in turn reinfect the pine trees, completing a “typical” rust cycle.

Silvicultural practices may lessen the incidence of infection in plantations. Avoid planting highly susceptible species such as slash and loblolly pines in areas of known high rust incidence. In these areas more resistant species such as longleaf or shortleaf pine should be planted. Pruning infected branches will prevent stem infection in young plantations. Rust-resistant pines should be readily available from the nurseries in the near future. Culling out seedlings with obvious galls before outplanting will reduce the disease incidence in new plantations.

WHITE PINE BLISTER RUST

White pine blister rust, caused by _Cronartium ribicola_, was introduced to North America on nursery stock about 1900. It is the most important disease on white pine in the United States. In the South, the disease is found on eastern white pine in the Appalachian mountains.

The disease is caused by a fungus that attacks both white pine and wild and cultivated currant and gooseberry bushes, called _Ribes_. Both hosts must be present if the fungus is to complete its life cycle. Attack by the disease is followed by the development of cankers on the main stem or branches. Infected pines die when a canker completely girdles the main stem or when many of the branches are killed by girdling. The most conspicuous symptoms of the disease are the dying branches or crowns (“flags”) above the girdling cankers, and the cankers themselves.

Initially, a narrow band of yellow-orange bark marks the edges of the canker. Inside this band are small irregular dark brown scars. As the canker grows, the margin and bank of dark scars expand and the portion formerly occupied by the dark scars is now the area where the spores that infect _Ribes_ are produced. During the months of April through June white sacs or blisters containing orange-yellow spores (called aeciospores) push through the diseased bark. The blisters soon rupture and the orange-yellow spores are wind-dispersed for great distances. Generally, there is some tissue swelling associated with the canker, which results in a spindle-shaped swelling around the infected portion of the stem.

Loss of white pines from blister rust can be prevented by destroying the wild and cultivated _Ribes_ bushes. Bushes may be removed by uprooting by hand, grubbing with a hand tool, or with herbicides. Pruning infected branches on young trees will prevent stem infections and probably tree mortality.

COMANDRA BLISTER RUST

Comandra blister rust, caused by the fungus _Cronartium comandrae_, is a canker disease of hard pines. The disease presently occurs in widely scattered areas throughout the western, central, and southern United States. In the South, the primary hosts are loblolly, shortleaf, pond, and Virginia pine. Herbaceous plants of the genus Comandra, commonly known as false toadflax or comandra, are also attacked.

The fungus infects pines through the needles and grows from the needle into the branch or main stem where it forms a gall or canker. Dark orange-colored spores which are produced on the surface of the gall in the spring are wind-blown and infect the leaves or stems of the comandra plants. Two to three weeks after infection, urediospores are produced on the underside of the comandra leaf. These are wind-blown and can only infect other comandra plants. Eventually hair-like structures known as telia are produced on the comandra leaves and stems. The telia produce spores which are wind-blown and infect the pine host through the needle. The necessary combination of a susceptible pine host, the alternate host, and the pathogen is presently known to occur only in northern Arkansas, eastern Tennessee, and northern Alabama.

No effective method of controlling the disease in forest stands is presently known. Silvicultural or forest management practices which reduce the abundance of the alternate host offer promise of long term control. Maintenance of dense stands and heavy ground cover as a means of shading out the intermediate host plants, may be helpful in reducing rust damage in many areas.

EASTERN GALL RUST

Eastern gall rust, caused by the fungus _Cronartium cerebrum_, attacks many species of eastern hard pines. The disease ranges eastward from the Great Plains and is most severe in the South on Virginia and shortleaf pines. Like most rusts this fungus requires an alternate host in addition to its pine host. In this case oaks, especially the red oak group (black, red, scarlet and pin) are the alternate hosts. Damage to the oaks is generally not of economic importance as only the leaves are affected.

On pines the fungus causes the formation of globose to sub-globose galls. Canker formation occurs occasionally but mortality generally results from wind breakage at the gall rather than by canker formation as literally hundreds of galls may appear on a single tree. They are not lethal to the tree, but may ruin tree form and on a large stem they can lead to an open decayed wound, as decay fungi are often secondary invaders of rust infections. The shape of galls and the arrangement of the spore sacs filled with red-orange spores present a cerebroid (brain-like) appearance. During the spring the bright orange galls are very striking.

This disease is sometimes a problem in nurseries where seedlings are attacked and killed. This is where control efforts are concentrated. Fungicide protectants are applied to the seedling foliage to prevent infection from spores produced on oaks. Contact your local forestry extension agent or the nearest Division of Forest Pest Management for the latest recommendations. Under forest conditions, control is not economically feasible. Trees of poor form should be removed during thinning operations.

SOUTHERN CONE RUST

Southern cone rust is caused by the fungus _Cronartium strobilinum_. It has been reported to completely destroy slash and longleaf pine cone crops in Georgia and along the Gulf Coast from Florida to Texas.

Like most other rusts, the fungus requires oaks and pines to complete its life cycle. Although infection of oak leaves occurs annually, no significant economic damage is done to the oaks. Fungus spores produced on oak leaves infect the mature female pine flowers about the time of pollination (January-February). The fungus grows through the developing conelet causing it to swell abnormally. By early April or late May the infected cones are three to four times larger than the normal first-year cones and even exceed the maturing second-year cones in size. The swollen cone scales are reddish in color. Cavities in the cone filled with orange-yellow spores burst and the cones become orange-yellow. The swollen orange-yellow cones in the tree crowns can be easily distinguished from normal cones by an observer on the ground. By late summer most of the diseased cones have died and fallen.

Control at present is confined to seed orchards. Hydraulic spraying of the flowers with fungicides gives a significant reduction in infections. Consult your local forester, county extension agent or the nearest Forest Pest Management Office for current control recommendations.

PITCH CANKER

Pitch canker, caused by the fungus _Fusarium lateritium forma pini_, is rapidly becoming widespread throughout the South. The disease apparently is most serious on Virginia, slash and south Florida slash pine. The fungus also attacks shortleaf, pitch, and table-mountain pine.

Pitch canker may cause tree mortality. On Virginia pines the fungus reportedly enters through small insect wounds in the twigs or mechanical wounds in the bole. Shoots may be girdled and killed within a few weeks, but it takes a period of years for the fungus to girdle the bole of larger trees. On slash pine the disease apparently attacks plantations in wave years. During years of heavy attack the fungus can cause rapid crown deterioration in addition to causing bole canker infections. Cankers on leaders in the crown can result in death of two-thirds or more of the crown by mid-summer in a tree that appeared healthy in the spring. In the majority of tree infections only the leader and one or two laterals will be infected. The tree recovers in a few years with a crook in the bole as the only evidence of attack. Pitch cankers usually retain the bark and old cankers on the hole may be sunken. The most diagnostic characteristic of the disease, and the one that definitely separates it from similar disease, is the heavy pitch soak of the wood beneath the canker. Pitch cankers are often so soaked with pitch that heavy flow of pitch is observed flowing down the bole.

At the present time, no known method of control exists. Observations in slash pine plantations indicate that some trees are resistant while others range in their degree of susceptibility.

WOOD DECAY

Wood decay of southern forest trees is responsible for nearly 80 percent of all loss attributed to disease. This decay is caused by fungi which mainly attack heartwood in the central portion of stems, branches, and roots. Wood-rotting fungi gain entrance into the tree through broken branches, wounds, and damaged or exposed roots. Spores, which land at these damaged areas, germinate and produce a microscopic mycelium which attacks and spreads throughout the heartwood. The decay is caused by the action of the mycelium, which penetrate the cell walls and dissolve or alter the wood in various ways. Fungus development within the tree may continue for many years without any apparent effect on the growth of the host. Eventually the mycelium will aggregate and break through the bark to form the reproductive stage, either before or after the death of the host. The fruiting body (sporophore, conk) produces vast amounts of spores which are capable of spreading the fungus to other trees.

Heartrots may be separated into broad classes on the basis of the host portion attacked, such as root rots, root and butt rots, stem rots, and top rots. Decay fungi may be further separated into two broad classes based on their effect on wood. The first class causes white rots, decomposing all components of the wood and reducing it to a spongy mass with white pockets or streaks separated by firm wood. The second class, causing brown rots, utilize the cellulose, leaving the lignin more or less unaffected. This usually results in a rot which appears as some shade of brown.

The separation of wood decay fungi on the basis of their host range, the portion of the host attacked, and the type of rot produced are useful aids to a pathologist in determining a tentative identification of the fungus responsible for a particular type of rot. However, there are numerous fungi which cause decay, many of which are exceptions to the various methods of classification. This forces the pathologist to use microscopic examination and various artificial keys to arrive at the proper identification of a given rot-producing fungus.

RED HEART

The fungus, _Fomes pini_, is the cause of a heartrot of widespread distribution. Common names for the rot produced by this fungus are: red heart, red ring rot, or white peck. The disease is commonly associated with mature and over-mature conifers, especially Douglas fir, larch, spruce, and pine. In the southern United States, the fungus attacks all species of mature pine.

Generally, infection of all hosts occurs through dead branch stubs. Early stages of decay caused by _F. pini_ are characterized by a discoloration of the heartwood, often appearing light red to reddish brown. The advanced stages of heartrot appear as elongated white pockets or flecks, formed parallel to the grain and separated by apparently firm wood. Often the pockets become resin filled. On southern pine hosts, the conks are often bracket-like or hoof-shaped. The upper surface appears dull grey to dark brown, with concentric furrows parallel to the margin of the fruiting body. The lower side is a light brown to brownish gold, rimmed by a velvety golden brown margin. Swollen knots result from the living wood tissue trying to overgrow the knot where a conk is forming.

In southern forest stands, heartrot damage may be reduced by harvesting mature pines prior to the age of extreme susceptibility to fungus attack. Some degree of shade tree protection can be obtained by pruning dead and dying branches flush with the main stem. This will allow the knot to be quickly overgrown by sap wood, preventing the heartrot fungus from entering through the branch stub.

ANNOSUS ROOT AND BUTT ROT

Annosus root and butt rot is caused by the fungus _Fomes annosus_. This pathogen is common throughout coniferous stands of the North Temperate Zone. Hardwoods may be attacked, but damage is usually of minor consequence. In the South, the disease is most serious in pine plantations on sandy soils with low organic matter. All species of southern pine are susceptible. Slash and loblolly plantations are often severely affected.