A Guide To Common Tree Diseases

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Many tree diseases can be traced to underlying problems such as: drought, tightly surrounded trees fighting for soil nutrients and light, poor soil conditions, backfilling, compacted soil, and physical damage to tree trunks. Each of these conditions can make trees vulnerable to disease pathogens.

Root Based Diseases

American Chestnut Blight is the fungus responsible for nearly destroying the species of American chestnut in eastern forests. This blight continues to survive in roots even after trees have been killed many years in the past. There is no current cure. And, the fungus currently survives on the roots of chinkapin, Spanish chestnut, and post oak as a non-lethal parasite.

Amillaria Root Rot infects both hardwood and softwood trees. It also is responsible for killing vines and shrubs throughout North America. Amillaria root rot is thought to be the major cause of oak tree decline. This particular root rot attacks trees that are already weakened by climate, fungi or other pests.

Annosus Root Rot infects and usually kills conifers. It is found in the Eastern states and is also common in the South. The fungus enters by infecting freshly cut surfaces of stumps. It is rampant in thinned pine forests and it survives even when the tree is cut down, infecting the root collar, stumps, or slash. Lucidus Root and Butt Rot disease is most common in hardwoods. It displays a wide range of hosts such as: oaks, maples, hackberry, ash, sweetgum, locust, elm, mimosa, and willow. It is found mostly in hardwood forests where infested trees weaken for several years then die. Leaf And Spot Diseases

Anthracnose and Leaf Spot Disease is widely found in the hardwood trees of the Eastern States. Look for dead areas and leaf blotches. It attacks the American sycamore, black walnut, dogwood, and various white oaks. Anthracnose is extremely destructive in urban areas resulting in the death of shade trees.

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Dogwood Anthracnose Fungus frequently infects dogwoods in cool, wet, spring and fall weather, but also can be found during the spring and summer growing season. Winter damage and drought can weaken dogwood trees and increase the disease severity. Severe infections can cause death to both woodland and ornamental varieties.

Dutch Elm Disease attacks American and European elms with equal vigor. It is prevalent throughout the climate range of these trees. The fungus infection exhibits itself by clogging vascular tissues, prevention of water movement to the tree's crown, and results in the elm wilting and dying.

Fire Blight aggressively attacks apple and pear tree varieties. It has been known to attack cotoneaster, crabapple, hawthorne, mountain ash, ornamental pear, firethorn, plum, quince, and spiraea. Fire blight may affect many parts of the tree but will be first noticed on damaged leaves, which turn red, curl and die.

Powdery Mildew is a common fungus that will appear as white powder on leaf surfaces. The white powder is actually millions of fungal spores, which spread on air currents to cause new infestations. Powdery mildew attacks all varieties of trees.

Sooty Mold Disease appears like grease or chimney soot. It seldom damages the infected tree but remains unsightly. The cause is a dark fungi growing on the honeydew excreted by leaf sucking insects or from exuded material coming from the leaves of certain trees. Bark Based Diseases

Aspen Canker is a wound-invading fungus responsible for major damage to quaking aspen in Western States.

Bacterial Wetwood or Slime Flux presents itself as an area of trunk rot. A tree's mechanism for fighting this disease is to compartmentalize off the damage. Careful inspection will reveal weeping sap from an area of the rotting trunk. The weeping is a slow natural expelling of the organism trapped in the liquid sap. Slime flux requires a dark and damp environment at summer temperatures to prosper. Beech Bark Disease results in death for the American beach. The disease infects the tree when the bark is attacked and damaged by beech scale, which is classified as fungi.

Canker Rot is a particularly destructive fungus for red oaks, hickory, honey locust, white oaks, and several other hardwoods. Decay of the tree's heartwood is the most serious symptom. The fungi can also kill the cambium and decay local sapwood within three feet of the canker point.

Commandra Blister Rust attacks hard pines through a fungus growing in the inner bark. The fungus attacks hard pines but requires an unrelated host plant to jump from one pine to another.

Fusiform Rust results in tree death within five years if a stem infection occurs. Pine trees less than 10 years old are most at risk. The fungus needs an alternative host to complete its life cycle. Part of the fungus life cycle is spent attacking the pine's stems and branches, and the balance of its life in the green leaves of various species of oak. Sudden Oak Death, first reported in 1995, is a newly identified fungus which attacks tanoaks, California black oaks, and coastal live oaks. This fungus causes a bleeding canker on the stem or trunk of the infected tree.

Blight Diseases

Brown Spot Needle Blight causes mortality of longleaf pines. The pines are most at risk during the seedling stage.

Diplodia Pine Blight attacks exotic and native pines throughout Eastern and Central States. The fungus is rare in natural pine forests but severe in landscapes, windbreaks, and park planting areas. Look for brown, stunted new shoots displaying short, brown needles.

Dwarf Mistletoe is found on black spruce and lodge pole pines in the Northwest and Rocky mountains. Mistletoe is the most damaging disease in lodge pole pine forests, causing stunted growth and tree mortality. Insect Problems

Leaf and Twig Galls are bumps or growths caused by the attack of insects or mites. The common oak gall is most conspicuous on leaves, stems, and twigs of oak trees. While the galls may appear serious, they are harmless to the health of the oak.

Last Updated: December 19, 2011
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About Bill Washburn William "Bill" Washburn has a BA in advertising from the Art Center College of Design and has taught at the University of Southern California and Northrup University. Writing from a well-connected studio in the rural foothills of the west coast, he is a frequent speaker at local art associations and has published numerous articles discussing periods of art history and the fundamentals of drawing and painting. William is a master gardener who grows his own culinary herbs, organic heirloom vegetables and a variety of fruits. He writes frequently about his gardening experiences on his website Pioneer Dad. He is an accomplished advertising writer, fine art painter, and art director with more than 20 years' experience. 

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