Tree Damaging Diseases

  • Apple Scab
    • tree service wentzville

      Distribution:Apple scab, also called scurf or black spot, is found in most areas of the world where apples are grown. This disease is more prevalent in cool, humid areas with frequent rainfall and is less severe in semiarid regions of the world. Fruit growing regions east of the Rockies have favorable climates for apple scab. Some other diseases of apples are harder to control, but apple scab is considered one of the world's top ranking apple diseases and is probably coexistent with the host.

      Hosts: In addition to apple and crabapple, apple scab also may infect hawthorn, pear, mountain ash and loquat. Cultivars vary in their susceptibility to this disease.

      Damage: Apple scab decreases the aesthetic value of the host. It causes severe damage in apples by reducing the quality of the fruit, and in all hosts by weakening the tree through defoliation.

      Control Tips: Sanitation; Removal of all leaves, twigs and fallen fruit which may harbor the overwintering spores will probably not eliminate scab completely, but will reduce the potential for severe infections. Chemical control; Apple scab is primarily controlled by timely sprays or dusts with the proper fungicides. For an effective chemical control program the apple trees must be diligently sprayed or dusted before, during or immediately after damp rainy periods, from the time of bud break until all ascospores are discharged.

  • Cedar Apple Rust
    • cedar apple rust

      Distribution:Indigenous to North America, especially east of the Rocky Mountains, including southern Ontario and Quebec. It has been reported from Europe.

      Hosts: Apples and crabapples, eastern red cedar, southern red cedar, rocky Mountain juniper, redberry juniper, Utah juniper, and certain cultivars of Chinese and creeping junipers. Hawthorn, is uncommonly affected.

      Damage: Cedar-apple rust is the most economically important of the Gymnosporanguim rusts. Infected apples are unsalable. The potential economic loss is so great that several eastern states enacted laws requiring eastern red cedars near commercial orchards to be destroyed. The aesthetic value of ornamental crabapples is lost or diminished. Damage also occurs due to premature defoliation, which can result in dwarfing. Death of the branches or the entire tree can occur from repeated infections in very susceptible varieties such as Bechtel's crabapple. On junipers, especially Rocky Mountain juniper, the twigs usually die back above the gall. The seriousness of this damage depends upon the number of galls. Otherwise, the damage to junipers is primarily aesthetic.

      Control Tips:Cultural- The disease can be avoided by keeping the hosts separated (three to four miles: to prevent the completion of the life cycle. In practice this is not likely to be effective, since even if the native host plants are removed many susceptible ones are likely to be present in ornamental plantings. Plant resistant varieties of each host. Galls can be pruned out on junipers before the telial horns develop, but the infection may still be present in the quiescent stage. Avoid crowding of plants and overhead irrigation. Chemical- Four to six sprays of recommended fungicide should be applied at seven to ten day intervals when the telial horns are active. The first spray should be applied as soon as the leaves emerge in the spring.

  • Dothistroma Needle Blight of Pines
    • dothistroma needle blight of pines, missouri landscaping and tree service

      Distribution:This disease is known to occur in the following states: Alaska, Arizona, California, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, Ohio, Oklahoma, Oregon, Virginia, Washington, Wisconsin.

      Hosts: This disease is most prevalent on Austrian and ponderosa pines in the Great Plains. Other pines that can be affected include western white pine and red pine. Scotch pine is very resistant to this disease. The fungus occurs in natural pine stands, but is more prevalent in areas with planted pines such as windbreaks, roadsides, parks and Christmas tree plantations.

      Damage: This disease disfigures affected trees by causing premature needle loss thus reducing tree vigor and growth. Affected needles turn brown before dropping, destroying the aesthetic value of landscape trees. The presence of this disease in Christmas tree planting may make affected trees unsellable.

      Control Tips: Proper timing of fungicide application is essential for effective control of Dothistroma needle blight. An application of fungicide in mid-May will generally protect the susceptible second year needles. Another application in June will afford protection to current year needles. Annual control may not be necessary in areas where the disease is not a serious problem or weather conditions are unfavorable for disease development.

  • Oak Wilt
    • Certified Arborist, St. Charles and Wentzville Missouri

      Distribution:The oak wilt pathogen has not been found outside of the United States. It ranges from Texas and South Carolina, to Maryland and Pennsylvania, and into eastern Nebraska and central Minnesota. The pathogen is most common in the upper Midwest where it is believed it may have originated.

      Hosts: All oak species that have been tested (36 species) have been proven to be susceptible to the oak wilt fungus. This includes oaks which were either naturally infected or artificially inoculated. Other susceptible tree species include: the Chinese, American, and Spanish chestnut, Allegheny and bush chinkapin, tanbark oak and apple. Of these, only the Chinese chestnut was found to be naturally infected.

      Damage: Species in the red oak group are more susceptible to oak wilt than species in the white oak group. An infected red oak will commonly be completely wilted within a few weeks, whereas, an infected white oak may take two to four years to completely wilt, or even longer. Once a red oak is infected it never recovers, but one third to one half of infected white oaks may recover and grown normally. Infected red oaks typically begin to show symptoms of wilting and bronzing of leaves and premature defoliation of branch tips in the upper crown. The wilt symptoms progress rapidly down through the crown, turning the outer portion of the leaves a dull green, bronze, or tan color. The affected leaves often show a distinct line of transition between the necrotic and normal green tissues. This discoloration progresses toward the leaf base and the midrib, creating what appears as a "green island" of healthy tissue at the basal end of the leaf. Infected white oaks typically display symptoms which are more subtle. Early symptoms are often characterized by the wilting of foliage of individual branches. Leaves may turn yellow, but necrosis is usually limited to the margins of the leaf blade. Affected leaves may resemble normal autumn coloration. The death of individual branches over a period of several years can often result in a "stag-headed" appearance of the crown.

      Control Tips: There are injectable systemic fungicides available to control the spread to uninfected trees. Remove infected trees and severe root grafts by trenching between infected trees and uninfected trees.

  • Pine Wilt Disease
    • pine wilt disease

      Distribution:North America, Japan, China and Taiwan.

      Hosts: Scotch, Austrian and Jack pines are susceptible, red pines are moderately susceptible, and other pines and conifers have resistance.

      Damage: Ranges from occasional flagged branch on resistant conifers to sudden death of susceptible pines. Sap flow stops and the foliage color changes from green to yellow and then brown as the tissue dries out.

      Control Tips: Sprays are not very effective and not recommended. Remove infected trees and re-plant resistant species.

  • Powdery Mildews
    • tree diseases in missouri

      Distribution:Powdery mildews are probably the most common, conspicuous, widespread, and easily recognizable plant disease. They affect weeds, shrubs, fruit trees, and broad-leaved shade and forest trees. Experts place the number of powdery mildew species at between 125 and more than 300, on more than 7,000 host plants worldwide.

      Hosts:weeds, shrubs, fruit trees, and broad-leaved shade and forest trees.

      Damage:Some of the plant diseases caused by members of this family are among the most destructive diseases known, whereas other appear to be very mild and cause little damage. Symptoms associated with powdery mildew include; dwarfing and stunting, distortion, chlorosis, premature senescence and browning of leaves, subnormal growth rate, blemished or aborted fruits, and depressed yields. Often the leaves have a slight reddening and curling before the white cycelium is noticed. Mildew races capable of attacking resistant cultivars have been detected on plant groups such as rose that have been bred or selected for resistance.

      Control Tips:Cultural measure such as trimming, fertilizing, and cultivating, which stimulate and prolong succulent plant growth, encourage many powdery mildews. Over Crowding, watering late in the day, and planting small trees and shrubs in the dense shade of larger trees all favor the development of this disease. Powdery mildews can be minimized by providing adequate sunlight and air circulation around plants in the greenhouse and nursery as well as the home. Powdery mildews on the foliage of deciduous trees rarely merit control measures outside the nursery, but this disease can cause considerable damage to flowers and is a major problem on roses. When spraying is warranted, fungicides applied at 1 or 2 week intervals after symptoms are observed, depending on the severity of the problem.

  • Spruce Needle Drop
    • st charles county arborist tree specialist

      Distribution:The fungus that causes spruce needle drop has been previously identified in Europe. In North America, the fungus has been found in Wisconsin, Minnesota, Kansas, Missouri and Ontario. The fungus is found on spruce trees in both forest and landscape settings.

      Hosts: The fungus has been found on Colorado blue, Norway, and white spruce in Wisconsin, Minnesota, Kansas, Missouri and Ontario

      Damage: Symptoms of the disease include the yellowing and progressive loss of previous years' needles from the branches of spruce. As the needles drop, the crown thins and eventually entire branches become bare. The loss of needles results in slow growth and a weakened tree. Another characteristic of the fungus is the presence of the black fruiting bodies on the twigs in early spring.

      Control Tips: No fungicides have been registered for this organism. The spread of the disease can be slowed by removing affected branches and burning or chipping the diseased wood. In cases where the infection is severe and affects a large portion of the needles, the tree should be removed and the diseased wood burned or chipped.

  • Sycamore Anthracnose
    • sycamore tree specialist lake st. louis, MO

      Distribution:Sycamore anthracnose is widespread in the central and eastern United States.

      Hosts: Sycamore (Platanus occidentalis) is susceptible to this disease. London planetree (Platanus acerifolia) is resistant.

      Damage: Damage early in the season may be confused with frost injury. The early blighting may cause a second crop of new leaves to emerge. Later damage appears as brown areas along veins, midribs and leaf tips. Cankers may appear on twigs and branches and eventually girdle them and cause them to die. Trees affected by anthracnose for several consecutive years may be severely weakened, making them more susceptible to other stresses such as winter or drought.

      Control Tips: Sanitation may be a useful practice in some nursery situations. Twig and branch cankers should be pruned out and fallen leaves collected and destroyed. Chemical control may be advisable in some cases, especially in wet years where the disease has been a problem. Proper timing of chemical controls is of the upmost importance.

  • Tar Spot of Maple
    • Lake St. Louis Tree Service

      Distribution:Tar spot occurs wherever maples grow in moist environments in North America and is more common in the eastern part of the United States.

      Hosts: Maples reported to be susceptible to both species of tar spot are bigleaf, mountain, red, Rocky Mountain, silver and sugar. Sycamore and box elder are also susceptible to both fungi.

      Damage: Tar spot has a minor impact on the health of the tree but has quite a striking appearance. Open grown trees are seldom infected. In sheltered situations, such as in the forest, trees can be heavily infected and may defoliate prematurely.

      Control Tips: Removal of the leaves in fall will destroy over wintering inoculum. If necessary, spray with a copper fungicide when buds are opening. Repeat several times at 2-3 week intervals. Treatments are rarely justified.

  • Verticillium Wilt
    • o'fallon tree service and landscaping

      Distribution:Two species are responsible for damage on ornamental hosts. They are common soil-borne fungi and are facultative parasites. They exist as mycelia and produce unicellur light colored conidia. Active fungal growth in the host occurs only during a short time each growing season: summer temperatures tend to arrest disease development.

      Hosts: Verticillium spp. Infects over 300 hosts, including many woody ornamentals and garden and greenhouse crops. Among the most common ornamental hosts are maples, elms, redbud, magnolia and viburnum.

      Damage: Verticillium wilt causes sudden wilting of branches, yellowing of foliage, premature defoliation and stunting. Although symptoms vary with the host, sapwood of infected branches is typically streaked olive-green to black and a slime flux may develop on the bark. In cross section, vascular tissue appears as a darkened ring. Following the initial display of wilt symptoms, an infected tree may show no sign of the disease for several years.

      Control Tips: Cultural practices may reduce the pathogen population, but will not eliminate it. Verticillium wilt can be controlled by planting resistant hosts in areas where the pathogen has been known to occur. Pruning out dead branches and increasing host vigor may serve to keep symptoms in check.