Historic, Archive Document Do not assume content reflects current scientific knowledge, policies, or practices. 4993.9 FICS A fib Forest Insect & Disease Leaflet 152 UU..SS.. DDeeppaarrttmmeenntt of AAggrriiccuullttuurree ¢¢ FFoorreesstt SSeerrvviiccee 7 Cankers on Western Quaking Aspen ]/ David W Johnson, Jerome S. Beatty, and Thomas-E. Hinds i Quaking aspen (Populus tremuloides Michx.) is one of the most well-known tree species in the western United States (figure 1). It is found from the northern limit of trees in northwestern Alaska through the western United States and into northern Mexico. Quaking aspen is an aggressive pio- neer species that frequently colonizes burned sites, making it an important component of many western ecosys- tems. Aspen reproduces primarily by means of root suckers produced from buds on shallow roots. Over much of its western range, quaking aspen is a small to medium-sized, fast-growing, and generally short-lived tree. The species reaches its most splendid development in the Rocky Mountains of southern Colorado and northern Figure 1 — Aspen stand with trees damaged by black New Mexico, where some individual canker. trees can attain diameters of up to .9 m (3 ft) and a height of 30.5 m (100 ft), Long appreciated for its esthetic and and often live for more than 150 years. shade tree value and its importance However, average trees are consider- for wildlife, aspen is also capable of ably smaller and many stands begin to excellent growth and high yields and deteriorate after 80 years. thus is an important commercial tim- David Johnson is plant pathologist, USDA Forest Service, Renewable Resources, Forest Health Management Staff, Rocky Mountain Region, Lakewood, CO; Jerome Beatty is plant pathologist, USDA Forest Service, Forest Pest Management, Pacific Northwest Region, Portland, OR; and Thomas Hinds is a retired research plant pathologist. au AG. reas) “s NY) Canker Fungi ber species. However, aspen has one major drawback—its soft bark is easily Several wound-invading fungi cause wounded by abiotic factors, animals, the majority of damage to aspen. The and insects. Subsequently, these taxonomy of some of these organisms € wounds can be invaded by disease has changed in recent years and sever- organisms. In some areas of the Rocky al scientific and common names are in Mountains, for example, elk gnaw use (table 1). extensively on the bark, leading to rapid deterioration of the stand. Life History However, canker diseases are by far the most serious causes of tree mortal- Records indicate that aspen cankers, ity. with the exception of hypoxylon canker, are found throughout the Canker diseases are among the prima- western United States (table 1). ry agents in creating snags and creat- Surveys of sites in Colorado showed ing infection sites for decay fungi. In the following cankers present: sooty- turn, standing “dead and down” bark canker encountered on 93% of woody material provides biological sites sampled, cryptosphaeria canker diversity in stands and serves as habi- on 83%, and black canker on 80%. The tat for cavity-nesting animals and following incidences of canker were birds. Endemic levels of infection by found on almost 3,000 live trees: these organisms are essential to main- sooty-bark, 1.1%; cryptosphaeria, taining a balanced ecosystem and 1.1%; and black, 4.4%. More than half serve an important role in the dynam- of the tree mortality was attributed to ics and ecology of aspen stands. sooty-bark canker and one-fourth to Table 1—Common names of cankers and scientific names off ungi inciting the disease in western aspen* Preferred Other common name common names Scientific name Sooty-bark canker Cenangium canker Encoelia pruinosa (Ellis & Everh.) Torkelson & Eckblad (= Cenangium singulare) Cryptosphaeria Snake canker Cryptosphaeria populina (Pers.) canker Sacc. Black canker Ceratocystis or Ceratocystis fimbriata Ellis target canker & Halst. Cytospora canker Cytospora chrysosperma (Pers.:Fr.) Hypoxylon canker Hypoxylon mammatum (Wahlenberg) c J.H. Miller * Hawksworth FG, Gilbertson RL, Wallis GW. 1985. Common names for tree diseases in the western United States and western Canada. In: Proceedings, 23rd Annual Western International Forest Disease Work Conference, 1984 September 25-28; Taos, NM. 37 p. (suppl.) cryptosphaeria canker. Black canker The fungus infects trees through was found on only 9% of the dead wounds and invades the inner bark trees but was not considered responsi- and cambium. Cankers develop rapid- ble for tree mortality in every case. ly, extending as much as 1 m (3 ft) in @sypoxyton canker was not found on length and .3 m (1 ft) in width in a sites examined in this survey but was year. However, the mean annual observed in earlier surveys. Cytospora extension vertically is .4 m (18 in) and canker was not included in these sur- .2 m (6 in) horizontally. Young veys because the fungus is not a pri- cankers first appear on the bark as mary parasite on healthy trees, sunken oval areas. Formation of callus although it is commonly found on around canker margins is unusual, as injured and stressed trees. host tissues are rapidly colonized by the fungus. The bark killed each year itesGay.cle by the fungus is readily apparent and begins to slough after 2 or 3 years, Sooty-bark canker: Sooty-bark exposing the blackened inner bark. canker, the most lethal canker on This dead inner bark, which crumbles aspen in the West, is considered the to a soot-like residue in one’s hand, is most serious, for it tends to occur on the origin of the common name of this the larger trees on all sites. It is found canker (figure 2). The outer bark mainly on overmature trees (over 120 sloughs faster in the central portions, years old) but can kill all sizes, usually giving the canker a “barber pole” within 3 to 10 years. Cankers are most appearance (figure 3). Eventually the common in stands where the incidence bark falls off in long stringy strips, of wounding is high. TN \. 5r oigy HuMYm Y art.5 2 4 j ‘ y = } Bs | by - 5 BA : 4 ome t x. aat: Hy- » geamtia i 4 ae | he eet hs i \ «] | : Oif LRi wi 3 Hoel? » Ceamee)l if”e a f oe eet 2.e e |) (S| ae f af a| e ESa eee : j At Figure 2 — Sooty residue from infected Figure 3 — Sooty-bark canker exhibiting characteris- bark tissue. tic barber pole pattern of infection. revealing small, black, spotted areas snake, hence the common name on the bleached, dead wood where the “snake canker” (figure 5). Small trees fungal mycelia held the dead bark to may be killed within a year after infec- the wood. Woody tissues under the tion. Large trees may have cankers canker tend to dry out and, as a conse- that girdle branches and enlarge onto quence, are not decayed; however, the trunk. wind breakage at the canker is not unusual. Bark near canker edges usually becomes discolored light brown to Cup-shaped fruiting bodies of the fun- orange. The dead, black, stringy, soot- gus, called apothecia, develop on the like bark adheres tightly to the sap- surface of old dead inner bark (figure 4). wood and contains small, scattered, These light gray structures (about 3 mm lens-shaped, light-colored areas (figure 6). or 18 inch in diameter) open when wet. Spores are forcibly ejected and Flask-shaped fruiting bodies, called wind-disseminated when moisture perithecia, develop beneath bark dead and temperature conditions are favor- for more than 1 year. The perithecia able. These spores can cause new release spores during wet periods. infections. These spores colonize wounds, estab- lishing the fungus at a new site. Light- Cryptosphaeria canker: This canker orange-colored fruiting structures, causes branch, sprout, and sapling called acervuli, of the asexual state of mortality; trunk cankers; and discol- the fungus (Libertella sp.) are occasion- oration and decay of aspen stems. The ally found along the edges of the cankers are commonly long and nar- canker. row, spiralling around the tree like a = xveee. te ee Figure 4 — Cup-shaped fruiting bodies of Encoelia Figure 5 — Cryptosphaeria canker exhibiting the pruinosa, called apothecia, develop on the old typical snakelike pattern of infection. inner bark, The fungus eventually colonizes sap- decayed. However, the agent of black wood and then heartwood, resulting canker (Ceratocystis fimbriata) does not in discoloration and decay. The discol- | cause wood decay. oration may vary from gray and rown to yellow, orange, and even Following infection, a circular dead pink. Under ultraviolet light, the decay area develops on the trunk. In the exhibits yellow fluorescence. This fluo- spring, callus tissue develops during rescent material may contain toxic cambial activity and walls off the substances that aid the fungus in colo- _ infection. During the dormant season, nizing host tissues. the tissue formed earlier in response to infection is invaded and killed by The decay associated with the canker the fungus. Repetition of this annual predisposes infected trees to wind cycle over the years results in a target- breakage. shaped canker formed of successive rings of dead bark and wood. After Black canker: Black canker is a com- several years, the dead bark sloughs mon and easily recognizable canker of — off, exposing concentric rings of dead aspen throughout its range in the woody tissue. Old cankers can be West. This canker rarely kills trees irregular in shape, with massive folds because it develops so slowly; the of black, flaring dead bark, hence the major impacts are trunk deformity, name “black canker” (figure 7). cull, and predisposition to wind break- age. Conks of species of wood decay Perithecia are formed in the spring fungi may develop in dead portions of | along the border of the canker on tis- =) old cankers and wood may be sues dead at least a year, although t > =] Figure 6 — Lens-shaped, light-colored areas within Figure 7 — Black canker showing large callus folds. infected bark tissue on a cryptosphaeria canker. they form rarely and are difficult to the inner bark turns dark brown and see. Spores ooze from the perithecia in the sapwood underneath light brown. sticky masses and are often vectored The dead bark falls from the tree in to other wounded trees by insects. _ large pieces after 2 to 3 years. Boring insects often are found in the cankered area. Pimple-like fruiting bodies, called pycnidia, which exude orange to red- Cytospora canker: The fungus that _ colored spore masses in hairlike coils, causes this canker (Cytospora are produced during wet weather sev- chrysosperma) is weakly parasitic and eral weeks after infection. During normally attacks stressed trees. rains, these spores are partially Although C. chrysosperma is the most washed away and can spread into common canker fungus on aspen new wounds. Insects visiting infected throughout the tree’s range, the fun- trees may also vector the fungus. gus often is associated with other, more aggressive canker fungi. Small Perithecia are produced later in the twigs and branches can be killed with- same areas as where pycnidia devel- out the formation of a distinct canker. oped. These structures are the sexual Trunk cankers usually have an irregu- _ state of the fungus (Valsa sordida). lar outline, with sunken, orange- discolored perimeters (figure 8). Hypoxylon canker: Trees of all ages and sizes on all sites are attacked, but The first indication of infection is the _ usually in widely spaced stands. orange discoloration of the bark sur- Although the disease causes serious rounding the wound. After infection, mortality in localized areas, its overall € _ importance in the West remains to be determined. Hypoxylon canker is probably more widely distributed in the West than has been reported. Young cankers first appear as slightly sunken areas with irregular margins on the bark. The underside of diseased bark appears laminated or mottled black and yellowish white. The papery outer bark sloughs from older infec- tions, exposing a blackened, crumbly inner bark. The cortex in the central portion of older cankers cracks in a checkerboard fashion and sloughs in small patches (figure 9). _ Canker growth, usually greater in length than width, takes several years to girdle a tree. 7 Asexual spores are produced on small, bristlelike structures under the blis- Figure 8 — Cytospora canker showing irregular pat- tered outer bark. Cankers are easier to tern of infection and orange discoloration of bark identify after several years, when tissue. perithecia are formed in small, crust- with various cankers, indicating that like stroma up to 1.3 cm (1/2 in) the mortality would increase. across. Young stroma are covered with a grayish bloom that persists for Stands with a high proportion of | everal years. Spores discharged from cankered stems should be clearcut to perithecia during wet weather can ini- stimulate sucker production and tiate new infections. regeneration of the stand. Regulating Factors Because aspen is very susceptible to injury and infection by canker fungi, The only practical control for canker the installation of developed recre- diseases is to avoid wounding resid- ation sites in aspen stands should be ual stems during stand entries. discouraged. Infection of wounded live trees, and subsequent tree mortality can increase High-Value Trees dramatically in managed stands. In one study in Colorado and New Pruning diseased, dying, and dead Mexico, 20% of residual trees in par- branches on high-value trees should tially cut stands died 5 years after the aid in reducing fungus spread from stand was harvested. Trunk cankers infected branches into the stem. developing from infected logging Pruning tools should be disinfected injuries were the major cause of tree with alcohol or laundry bleach after death. Two years later, 40% of the each cut to prevent infection of subse- remaining residual trees were infected quent pruning wounds. Small cankers on stems can be removed by excising all infected bark so there are clean edges around the infection to stimulate callus growth. Wounds should be shaped into an ellipse to promote rapid healing. Assistance Landowners can get more information about identification and control by contacting a County Cooperative Extension agent, their local state forestry office, or the USDA Forest Service, Forest Pest Management (FPM). i | Figure 9 — Hypoxylon canker showing checkered bark. Juzwik J, Nishijima WT, Hinds TE. 1978. References Survey of aspen cankers in Colorado. Plant Disease Reporter 62(10):906-910. Hinds TE. 1972. Ceratocystis canker of aspen. Phytopathology 62(2):213-220. Walters JW. 1984. An aid to identifying aspen diseases frequently encountered in the € Hinds TE. 1981. Cryptosphaeria canker and Rocky Mountains. U.S. Department of libertella decay of aspen. Phytopathology Agriculture. 20 p. 71(11):1137-1145. Walters JW, Hinds TE, Johnson DW, Beatty J. -Hinds TE. 1985. Diseases. In: DeByle NV, 1982. Effects of partial cutting on diseases, Winokur RP, eds. Aspen: Ecology and man- mortality, and regeneration of Rocky agement in western United States. Tech. Rep. Mountain aspen stands. Res. Pap. RM-240. RM-119. Fort Collins, CO: USDA Forest Fort Collins, CO: USDA Forest Service, Service, Rocky Mountain Forest and Range Rocky Mountain Forest and Range Experiment Station: 87-106. Experiment Station. 12 p. Hinds TE, Laurent TH. 1978. Common aspen diseases found in Alaska. Plant Disease Reporter 62(11):972-975. Hinds TE, Ryan MG. 1985. Expansion of sooty-bark and ceratocystis cankers on aspen. Plant Disease 69:842-844. cee Pesticides used improperly can be injurious to humans, animals, and plants. Follow directions and read all precautions on the labels. Consult your local forest pathologist, county agricultural agent, or State extension agent about restrictions and registered uses of particular pesticides. 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