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There are over 30 common tree diseases that contribute to health decline and death of most of the trees in the United States. This list of tree diseases causes most tree health problems and death and are very specific to either a conifer or a hardwood host.

These diseases are the cause of significant replacement expense of yard trees but take a major toll on the commercial expense of future losses of forest products. Some of these diseases are more of a problem for landscape tree specimens and yard tree planting. Others have been devastating to forest tree communities and single tree species.

American Chestnut Blight – Attacks hardwoods – Chestnut blight is a fungus that has virtually wiped out the American chestnut, as a commercial species, from eastern hardwood forests. Although roots from trees cut or killed many years ago continue to produce sprouts that survive to the sapling stage before being killed, there is no indication that a cure for this disease will be found. The fungus is widespread and continues to survive as a non-lethal parasite on chinkapin, Spanish chestnut, and post oak.

Armillaria Root Rot – Attacks hardwoods and conifers –  Armillaria attacks hardwoods and softwoods and kills shrubs, vines, and forbs in every state. It is pervasive in North America, commercially destructive, a major cause of oak decline. The Armillaria sp. can kill trees that are already weakened by competition, other pests, or climatic factors. The fungi also infect healthy trees, either killing them outright or predisposing them to attacks by other fungi or insects.

Anthracnose and Leaf Spot Diseases – Attacks hardwoods – Anthracnose diseases of hardwood trees are widespread throughout the Eastern United States. The most common symptom of this group of diseases is dead areas or blotches on the leaves. The diseases are particularly severe on American sycamore, the white oak group, black walnut, and dogwood. The greatest impact of anthracnose is in the urban environment. Reduction of property values results from the decline or death of shade trees.

Annosus Root Rot – Attacks conifers – The disease is a rot of conifers in many temperate parts of the world. The decay, called annosus root rot, often kills conifers. It occurs over much of the Eastern U.S. and is very common in the South. The fungus, Fomes annosus, usually enters by infecting freshly cut stump surfaces. That makes annosus root rot a problem in thinned pine plantations. The fungus produces conks that form at the root collar on roots of living or dead trees and on stumps or on slash.

Aspen Canker – Attacks hardwoods – Quaking aspen (Populus tremuloides Michx.) is one of the most well-known and widespread tree species in the western United States. Several wound-invading fungi cause the majority of damage to aspen. The taxonomy of some of these organisms has changed in recent years and several scientific and common names are in use.

Bacterial Wetwood (slime flux) – Attacks hardwoods – Slime flux is a major bole or trunk rot. The tree is trying its best to compartmentalize off the damage. “Weeping” sap from the rotting point is what you are seeing. This bleeding is a protective slow, natural draining effect on a destructive organism that needs a dark, damp environment with favorable culturing conditions at summer temperatures. One interesting thing is that the weeping liquid is the fermented sap, is alcohol-based, and is toxic to new wood.

Beech Bark Disease – Attacks hardwoods – Beech bark disease causes significant mortality and defect in American beech, Fagus grandifolia (Ehrh.). The disease results when bark, attacked and altered by the beech scale, Cryptococcus fagisuga Lind., is invaded and killed by fungi, primarily Nectria coccinea var. faginata.

Brown Spot in Longleaf Pine – Attacks conifers – Brown-spot needle blight, caused by Scirrhia acicola, delays growth and causes mortality of longleaf pine (Pinus palustris Mill.). Brown spot reduces the ​total annual growth of southern pines by more than 16 million cubic feet (0.453 million cubic meters) of timber. Damage is most severe on longleaf seedlings in the grass stage.

Canker Rot – Attacks hardwoods – Canker-rot fungi cause serious degrade and cull in hardwoods, especially the red oaks. Heartwood decay is the most serious form of damage, but the fungi also kill the cambium and decay the sapwood for as much as 3 feet above and below the canker point into the tree. Canker-rots are most important on the red oaks, but also occur on hickory, honey locust, some white oaks, and other hardwoods.

Commandra Blister Rust – Attacks conifers – Comandra blister rust is a disease of hard pines that is caused by a fungus growing in the inner bark. The fungus (Cronartium comandrae Pk.) has a complex life cycle. It infects hard pines but needs an alternate host, an unrelated plant, to spread from one pine to another.

Cronartium Rusts – Attacks conifers – Cronartium is a genus of rust fungi in the family Cronartiaceae. They are heteroecious rusts with two alternating hosts, typically a pine and a flowering plant, and up to five spore stages. Many of the species are plant diseases of major economic importance, causing significant damage.

Diplodia Blight of Pines – Attacks conifers – This disease attacks pines and is most damaging to plantings of both exotic and native pine species in 30 Eastern and Central States. The fungus is seldom found in natural pine stands. Diplodia pinea kills current-year shoots, major branches, and ultimately entire trees. The effects of this disease are most severe in landscape, windbreak, and park plantings. Symptoms are brown, stunted new shoots with short, brown needles.

Dogwood Anthracnose – Attacks hardwoods – An anthracnose fungus, Discula sp., has been identified as the causal agent for dogwood anthracnose. Infection of dogwoods is favored by cool, wet spring and fall weather, but can occur throughout the growing season. Drought and winter injury weaken trees and increase disease severity. Consecutive years of heavy infection have resulted in extensive mortality in both woodland and ornamental dogwoods.

Dothistroma Needle Blight – Attacks conifers – Dothistroma blight is a devastating foliar disease of a wide range of pine species. The causal fungus, Dothistroma pini Hulbary, infects and kills needles. Premature defoliation caused by this fungus has resulted in complete failure of most ponderosa pine plantings in States east of the Great Plains.

Dutch Elm Disease – Attacks hardwoods – Dutch elm disease primarily affects American and European species of elm. DED is a major disease problem throughout the range of elm in the United States. The economic loss resulting from the death of high-value urban trees is considered by many to be “devastating”. Fungus infection results in clogging of vascular tissues, preventing water movement to the crown and causing visual symptoms as the tree wilts and dies. American elm is highly susceptible.

Dwarf Mistloe – Attacks conifers – Trees favored by dwarf mistletoe (Arceuthobium sp.) are certain conifers, mainly black spruce and lodgepole pine. Dwarf mistletoe infests significant stands of black spruce in the northern U.S. and lodgepole pine in the Northwest and the ​Rocky Mountains. This mistletoe is the most damaging disease agent in lodgepole pine, causing severe growth loss and increased tree mortality. It is estimated to infest 15 percent of all black spruce stands in the north-central states.

Elytroderma Needle Cast – Attacks conifers – Elytroderma deformans is a needle disease that often causes witches brooms in ponderosa pine. It is sometimes mistaken for dwarf mistletoe. The disease is restricted to “hard” or “two- and three-needle” pine species. Elytroderma needle cast has also been reported in North America on lodgepole, big-cone, jack, Jeffrey, knobcone, Mexican stone, pinyon, and short-leaf pine.

Fire Blight – Attacks hardwoods – Fire blight is a serious disease of apple and pear. This disease occasionally damages cotoneaster, crabapple, hawthorn, mountain ash, ornamental pear, firethorn, plum quince and spiraea. Fire blight, caused by the blight bacterium Erwinia amylovora, can affect many parts of a susceptible plant but generally noticed first on damaged leaves.

Fusiform Rust – Attacks conifers – This disease causes death within five years of a tree’s life if a stem infection occurs. Mortality is heaviest on trees less than 10 years old. Millions of dollars are lost annually to timber growers because of the disease. The fungus Cronartium fusiforme requires an alternate host to complete its life cycle. Part of the cycle is spent in the living tissue of pine stems and branches, and the remainder of the green leaves of several species of oak.

Galls on Leaf and Twig – Attacks hardwoods – Leaf infections called “galls” are bumps or growths caused by the feeding of insects or mites. One particularly common version of this rapid explosion of growth is called the common oak gall and is most noticeable on the leaf, stem, and twig of an oak tree. Although these galls may look like a serious problem, most are harmless to the overall health of the tree.

Laminated Root Rot – Attacks conifers – The disease Phellinus weirii occurs in patches (infection centers) sporadically distributed in clusters throughout its range. The most susceptible hosts are Pacific silver fir, white fir, grand fir, Douglas-fir, and mountain hemlock.

Littleleaf Disease – Attacks conifers – Littleleaf disease is the most serious disease of shortleaf pine in the Southern United States. Affected trees have reduced growth rates and usually die within 6 years. The disease is caused by a complex of factors including the fungus Phytophthora cinnamomi Rands, low soil nitrogen, and poor internal soil drainage. Often, microscopic roundworms called nematodes and species of the fungal genus Pythium are associated with the disease.

Lucidus Root and Butt Rot – Attacks hardwoods – Lucidus root and butt rot disease is one of the most common root and butt rots of hardwoods. It has a wide host range including oaks, maples, hackberry, ash, sweetgum, locust, elm, mimosa, and willows, and is found throughout hardwood forests. Host trees normally decline for a variable period of time and then die.

Mistletoe (Phoradendron) – Attacks conifers and hardwoods – Members of the genus are parasites of conifer and hardwood trees and shrub in the Western Hemisphere. There are seven species of native true mistletoe that are found on hardwoods in many parts of Eastern, Western, and Southern United States. The one most commonly known and widespread is P. serotinum (also known as P. flavescens) which occurs mainly in the East and Southeast.

Oak Wilt – Attacks hardwoods – Oak wilt, Ceratocystis fagacearum, is a disease that affects oaks (especially red oaks, white oaks, and live oaks). It is one of the most serious tree diseases in the eastern United States, killing thousands of oaks each year in forests and landscapes. The fungus takes advantage of wounded trees – the wounds promote infection. The fungus can move from tree to tree through roots or by insects. Once the tree is infected there is no known cure.

Powdery Mildew – Powdery mildew is a common disease that appears as a white powdery substance on the leaf surface. The powdery appearance comes from millions of tiny fungal spores, which are spread in air currents to cause new infections. It attacks all kinds of trees.

Scleroderris Canker – Attacks conifers – Scleroderris canker, caused by the fungus Gremmeniella abietina-Scleroderris lagerbergii (Lagerb.) Morelet, has caused extensive mortality in conifer plantations and forest nurseries in the northeast and north-central United States and eastern Canada.

Sooty Mold – Sooty mold appropriately describes the disease, as it looks just like chimney soot. Although unsightly, it seldom damages the tree. The pathogens are dark fungi growing either on the honeydew excreted by sucking insects or on exuded material coming from leaves of certain trees.

Sudden Oak Death – Attacks hardwoods – A phenomenon known as Sudden Oak Death was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks (Lithocarpus densiflorus), coast live oaks (Quercus agrifolia), and California black oaks (Quercus kelloggii) have been killed by a newly identified fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the stem.

Thousand Cankers Disease – Attacks hardwoods – Thousand cankers disease is a newly discovered disease of walnuts including black walnut. The disease results from the walnut twig beetle (Pityophthorus juglandis) hosting a canker producing fungus in the genus Geosmithia (proposed name Geosmithia morbida). The disease was thought to be restricted to the western United States where over the past decade it has been involved in several large-scale die-offs of walnut, particularly black walnut, Juglans nigra. Unfortunately, it has now been found in eastern Tennessee.

Verticillium Wilt – Attacks hardwoods – Verticillium wilt is common in many soils and affects several hundred herbaceous and woody plant species. Ash, catalpa, maple, redbud and yellow poplar are most frequently infected trees in the landscape but rarely in natural forest conditions. This disease can become a serious problem on susceptible hosts in infested soils but many tree varieties have been developed with some resistance.

White Pine Blister Rust – Attacks conifers – The disease attacks pines with 5 needles per fascicle. That includes Eastern and Western white pine, sugar pine and limber pine. Seedlings are in greatest danger. Cronartium ribicolais a rust fungus and can only be infected by basidiospores produced on Ribes (currant and gooseberry) plants. It is native to Asia but was introduced to North America. It has invaded most white pine areas and is still making progress into the Southwest and into southern California. Attacks hardwoods – Leaf infections called “galls” are bumps or growths caused by the feeding of insects or mites. One particularly common version of this rapid explosion of growth is called the common oak gall and is most noticeable on the leaf, stem, and twig of an oak tree. Although these galls may look like a serious problem, most are harmless to the overall health of the tree.


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