Tree Diseases in the Nashville Area

Tree Diseases

Tree diseases on shade trees and small ornamental trees may just make your trees look bad and cause no long-term damage to the tree. Some diseases can seriously disfigure trees, while others are deadly.

We have noted which diseases you should take seriously by noting Call an Arborist.

If you aren’t sure, give us a call and we will inspect your trees for you.

Anthracnose

Anthracnose tree diseases attack the foliage and twigs of trees in late spring and early summer. Cool, wet weather favors infection and spread of these diseases. Ash, dogwood, maple and sycamore may be damaged by anthracnose diseases caused by a variety of fungi. The canopy of affected trees may be visibly thinned. Angular leaf spots, dead leaf tissue delineated by veins, twig dieback and cankers on small branches are common. Repeated defoliation may weaken trees and lead to death. Anthracnose diseases of maple and ash occur sporadically and are seldom a serious threat. Ash anthracnose may cause 50 percent defoliation within a few days of infection. (call an arborist)

Leaf Blister/Curl

Leaf blister and leaf curl refer to foliar tree diseases in which young, expanding leaves are infected. Symptoms include raised blisters for oak leaf blister and fleshy, distorted leaves for peach leaf curl. Affected leaves usually remain on the tree and function normally.

Leaf Spots

Numerous fungal leaf spot diseases affect trees and a few bacterial leaf spot diseases:

Scab- Call an Arborist

Scab is a disease of crabapple. Olive-brown spots develop on the leaves and fruit of susceptible crabapple cultivars. Scab may cause severe defoliation and loss of vigor.

Tar spot is a tree disease of maple where the fungal pathogen looks like a raised, tar-like substance on the upper surface of infected leaves. Tar spot occurs on sugar and silver maple, but is not a serious threat to either.

Bull’s eye leaf spot– Call an Arborist
Bulls Eye Leaf Spot may be found on maple, magnolia, sassafras and other trees. Target-shaped spots with concentric rings appear on leaves. This disease may cause premature leaf drop.

Leaf blotch
Leaf blotch is a fungal tree disease of horse-chestnut and buckeye. Irregular leaf spots and symptoms that mimic leaf scorch (marginal leaf burn) appear in mid to late summer. Ohio, red and yellow buckeye are susceptible to leaf blotch; however, bottle brush buckeye is moderately resistant.

Shot hole diseases of ornamental cherry may be caused by fungi or bacteria. The symptoms appear as circular lesions in which the diseased tissue falls out of the leaf, causing a “shot hole” effect. These diseases are worse during wet weather or on trees irrigated with overhead irrigation.

Miscellaneous leaf spot diseases caused by fungi such as Phyllosticta and Septoria are sometimes found on trees as diverse as Japanese maple, magnolia, birch, flowering dogwood and sourwood. An extremely wet spring can trigger infection and spread of these fungi. Damage is often cosmetic and the effects of these diseases are minimal unless the
damage occurs annually and results in premature defoliation.

Needlecast

Conifers such as pine, spruce and fir may be attacked by needlecast diseases that result in severe needle drop. Most needlecast diseases attack older needles. Infected trees may have brown needles in the interior of the tree’s canopy. Symptoms often develop at the base of the canopy and move upward. Once needles are cast, infected trees generally have thin canopies. Black, fungal-fruiting bodies are easy to observe on infected needles within the canopy or on needles that have been cast.

Powdery Mildew

White-to-gray powdery fungal growth blankets the leaves of trees infected with powdery mildew. This disease may be observed on oaks, tulip poplar, sycamore, crabapple and dogwood. Shade trees such as oak and tulip poplar are not seriously injured by powdery mildew since it appears in late summer or early fall. Powdery mildew is more than just an aesthetic problem for flowering dogwood, as it appears in early summer and reduces shoot growth and trunk caliper.

Sooty Mold

Black fungal growth on the upper surfaces of leaves and branches is usually associated with sooty molds. These fungi live on the excrement or “honey dew” of aphids or scale insects. Trees with sooty mold should be closely examined for insect infestations.

Rusts

Several rusts affect shade and ornamental trees:

Pine needle rust appears in late spring on Eastern white pine on last year’s needles. Although widespread on the needles of isolated trees, it is not considered a serious threat, as the damage occurs before current season’s growth.

Cedar-apple rust can be found on apple, crabapple and Eastern red cedar. Each spring spores are released from galls on cedar that infect the leaves and fruit of flowering crabapple. Later in the summer a different spore is produced on the leaves of crabapple that infect single needles of cedar. These infected needles will swell into galls that will release spores during warm, wet weather in the spring. Highly susceptible cultivars of crabapple such as ‘Bechtel’s’ may be seriously damaged, but you will find only scattered yellow-to-gold leaf spots on most susceptible cultivars. Cedar-apple rust may cause premature leaf drop on some cultivars.

Cedar-hawthorne rust can cause severe deformation of the leaves, twigs and fruit of hawthorne. As with cedar-apple rust, infective spores from Eastern red cedar infect all
aboveground parts of hawthorne. Orange-to-salmon colored spores are produced from tubes on infected fruit and twigs.

Canker Tree Diseases

Localized infection on the trunk or branches of trees is usually the result of canker diseases. Cankers may appear as sunken areas or swollen areas on infected branches. Most canker diseases are caused by fungi, but there are a few bacterial canker diseases. The fungi that cause canker diseases will often colonize the bark of newly planted trees under water stress. If a canker disease girdles the entire branch or trunk, all growth beyond the canker will die.

Botryosphaeria canker is a common disease causing branch dieback on trees as diverse as ash and Leyland cypress. Trees affected by drought stress are particularly susceptible. Sunken cankers are the most common symptom on broadleaf trees and bleeding, resinous cankers may be found on the branches and trunks of conifers.

Endothia canker is often associated with oaks infested with obscure scale. Bright orange fruiting bodies of the fungus are easily spotted on cankered branches.

Nectria canker is a perennial canker that may be found on dogwood, linden and black walnut. Callus tissue forms at the margin of the canker each year. As this is repeated over several
years, concentric rings of callus tissue are visible at the site of infection. When the canker girdles the trunk, all the tissue above the canker dies.

Seiridium canker is quickly becoming a serious disease on Leyland cypress. Trees growing on dry sites are more susceptible to this disease. The symptoms are very similar to botryosphaeria canker. Severely affected trees are so disfigured that they need to be replaced.

Black knot is an important disease of ornamental plum and black cherry. Black, rough galls or “knots” form on the branches of the host. Infection usually occurs on succulent growth in the spring by spores spread by air currents from nearby trees with black knot.

Fire blight is a bacterial disease that can cause severe damage to crabapple, pear and serviceberry. Bacteria may be spread at flowering in the spring by insect pollinators. Infected shoots die so quickly that several inches of the twig may collapse, forming a “shepherd’s crook” symptom. Diseased shoots may be killed back to larger branches where cankers form. The bacterium overwinters in these cankers.

Vascular Wilts

Several diseases affect the conductive tissues of trees that transport water, nutrients and complex sugars produced in photosynthesis. Once these pathogens invade this conductive or vascular tissue, they severely reduce the flow of water and anything that may be transported. Most trees infected by vascular wilt diseases decline and die after several years.

Verticillium wilt is a fungal disease that can attack many trees, with maples being the most important hosts. Verticillium is soil-borne and may persist many years in the absence of a
host. The fungus usually enters through wounds in the roots and then moves through the vascular system. Symptoms can be quite variable, but yellow leaves are often followed by wilting and death of entire branches. Occasionally, the entire crown may wilt and die. Green-to-brown discoloration may be found in the outer sapwood of some tree species.

Dutch elm disease is one of the best known diseases that affect shade trees. The pathogen was introduced into this country in the 1930s. Dutch elm disease destroyed millions of American elm that were planted in a virtual monoculture along city streets. It is spread by elm bark beetles and through root grafts from diseased to healthy trees. Symptoms include wilting, yellowing and browning of leaves. As with verticillium wilt, brown discoloration may be observed in the sapwood of infected ranches. Infected trees may die within a few weeks of infection.

Bacterial leaf scorch attacks mature pin oak, but also infects red maple, sycamore, mulberry and elm. The bacterium like pathogen is spread by leaf hoppers that have acquired the pathogen from an infective host. Leaf scorch is the first symptom observed. Diseased trees may decline for several seasons so that leaves are only found on the trunk and large branches near the interior of the crown.

Phytophthora Root Rot
Root rot diseases may stunt the growth of trees and in some cases be lethal. Fir, spruce, pine, Leyland cypress, dogwood and maple are all hosts of phytophthora. This fungus is a“water mold” that is favored by wet, poorly drained soils. Also, excessive irrigation favors disease development. Infected trees may have yellow needles or leaves that are smaller than normal. Dark, decayed roots may be found on diseased trees.