32 Common Tree Diseases

Discover the major common tree diseases in the United States.

A close-up of a grapevine leaf with yellow and brown patches infected by grapevine fungal disease downy mildew.

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Some tree diseases, if severe enough, can take a devastating toll on forest tree communities, as well as single species. The following list contains diseases that cause the most tree health problems in the United States. These diseases are specific to either a conifer or a hardwood host.

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Armillaria Root Rot

Armillaria root rot on a tree.

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Armillaria attacks both hardwoods and softwoods and causes either yellowing leaves or browning needles. Wood that is decaying from armillaria root rot may soften and become white before the tree eventually dies. Trees that are healthy can be killed outright by this disease; if not, they are weakened and predisposed to attacks by other fungi or insects.

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American Chestnut Blight

Chestnut blight is a fungus that has virtually wiped out the American chestnut commercial species from eastern hardwood forests. Although roots that were cut or killed many years ago continue to produce sprouts that survive until the sapling stage, 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.

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Anthracnose and Leaf Spot Diseases

Anthracnose on the green leaf of Robusta coffee plant tree.

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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 urban environments. The decline or death of shade trees due to this disease has reduced property values.

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Annosus Root Rot

Annosus root rot can impact conifers in many temperate parts of the world. 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 the roots of living or dead trees and on stumps or slashes.

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Aspen Canker

Hypoxylon canker on quaking

Greg Blick / Flickr / CC BY-NC-ND 2.0

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, such as cankers. The taxonomy of some of these organisms has changed in recent years and several scientific and common names are in use.

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Brown-Spot Needle Blight

Brown needles on a pine tree.

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Brown-spot needle blight, caused by Scirrhia acicola, delays growth and causes mortality of longleaf pine (Pinus palustris). 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.

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Canker Rot

Canker rot typically attacks oak trees, producing yellow or yellow-brown fruiting bodies that soon after degrade. The disease starts at the heartwood of a tree and attacks outward.

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Commandra Blister Rust

Comandra blister rust is a disease of hard pines that is caused by a fungus growing in the inner bark. It is a management concern in various parts of Canada and the United States, according to the USDA Forest Service. The fungus (Cronartium comandrae) requires an alternate host in order to spread from one pine to another.

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Cronartium Rusts

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.

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Diplodia Blight of Pines

This disease kills current-year shoots, major branches, and ultimately entire trees, primarily pines. The effects of this infection are most severe in landscapes, windbreaks, and park plantings. Symptoms include the development of brown, stunted new shoots with short, brown needles.

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Dothistroma Needle Blight

Dothistroma needle blight as shown on these pine needles.

U.S. Department of Agriculture / Flickr / CC BY 2.0

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

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Dutch Elm Disease

Dutch elm disease (DED) primarily affects American and European species of elm. DED is a major problem throughout the range of elm in the United States. The fungal infection results in the clogging of vascular tissues, which prevents water movement to the crown and causes visual symptoms as the tree wilts and dies. American elm is highly susceptible to this disease.

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Dwarf Mistloe

Trees favored by dwarf mistletoe (Arceuthobium sp.) are 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.

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Elytroderma Needle Cast

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.

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Beech Bark Disease

Detail image of a tree affected by Beech Bark Disease.

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Beech bark disease causes significant mortality and defect in American beech, Fagus grandifolia. The disease results when bark, attacked and altered by the beech scale, Cryptococcus fagisuga, is invaded and killed by fungi, primarily Nectria coccinea var. faginata.

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Fire Blight

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 is generally noticed first on damaged leaves.

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Fusiform Rust

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.

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Galls on Leaf and Twig

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. It 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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Laminated Root Rot

Laminated root rot is a disease that occurs in patches sporadically distributed in clusters throughout its range. The most susceptible hosts are Pacific silver fir, white fir, grand fir, Douglas-fir, and mountain hemlock.

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Dogwood Anthracnose

Dogwood anthracnose causing green leaves to turn brown.

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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 injuries weaken trees and increase disease severity. Consecutive years of heavy infection have resulted in extensive mortality in both woodland and ornamental dogwoods.

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Littleleaf Disease

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, 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.

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Lucidus Root and Butt Rot

Lucidus root and butt rot disease are 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.

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Bacterial Wetwood

Bacterial wetwood, also known as slime flux, is a major bole or trunk rot. The tree, when infected, tries its best to compartmentalize the damage by "weeping" sap. This bleeding has a protective, slow, naturally draining effect on the destructive organism, which needs a dark, damp environment with favorable culturing conditions at summer temperatures. The weeping liquid is fermented sap, is alcohol-based, and is toxic to new wood.

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There are seven species of native true mistletoe that are found on hardwoods in many parts of the 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.

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Oak Wilt

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 fungus can move from tree to tree through roots or by insects. Once the tree is infected, there is no known cure.

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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.

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Scleroderris Canker

Scleroderris canker has caused extensive mortality in conifer forests in the northeast and north-central United States and eastern Canada. The two North American strains, according to the USDA Forest Service, are the European and the Lake States strains.

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Sooty Mold

Sooty mold

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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.

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Sudden Oak Death

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.

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Thousand Cankers Disease

Thousand cankers disease is a newly discovered disease of walnut trees, including black walnut. The disease results from the walnut twig beetle (Pityophthorus juglandis) hosting a canker-producing fungus in the genus Geosmithia. 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. Unfortunately, it has now been found in eastern Tennessee.

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Verticillium Wilt

Verticillium wilt is common in many soils and affects several hundred herbaceous and woody plant species. Ash, catalpa, maple, redbud, and yellow poplar are the 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.

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White Pine Blister Rust

White pine blister rust attacks pines with five needles per fascicle; this includes eastern and western white pine, sugar pine, and limber pine. Seedlings are in the greatest danger.

This rust fungus 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.