Poplar Tree Cankers – Learn About Canker Disease In Poplar Trees

Poplar Tree Cankers – Learn About Canker Disease In Poplar Trees

By: Jackie Carroll

Cankers are physical deformities that may indicate a serious poplar tree disease. Learn about canker disease in poplar trees in this article.

Cankers on Poplar Trees

The microscopic organisms that cause poplar tree diseases enter the tree through wounds and breaks in the bark. A canker, or dark, sunken area on a branch or trunk, gradually spreads around the tree. If it grows to cover half or more of the circumference of the trunk, the tree will probably die. Cankers on branches cause the branch to wither and die, and the disease can spread to the trunk.

You can’t cure canker diseases of poplar, but you may be able to keep them from spreading and further damaging the tree. It’s also important to prevent the disease from spreading to nearby trees. Weak, sickly trees are more likely to develop cankers than strong, healthy ones. If a single tree has canker problems, you might want to consider removing the sick tree to save surrounding trees.

The most common canker tree diseases look similar, but they are likely to attack different species. Here is a short list of diseases that cause poplar tree cankers:

  • You’re most likely to find Cytospora chrysosperma and Leucocytospora nivea on Simon, Carolina, Lombardy and Silver-leaf poplars, but the other species of poplar can get a mild case of the disease too.
  • Crytodiaporthe populea is most severe on Lombardy poplar trees. Most other species are resistant.
  • Hypoxylon mammatum infects white poplars. You’ll also find it on quaking and European aspens and pussy willows.

Treating/Preventing Poplar Canker Diseases

Keeping your trees healthy is the first step in preventing canker diseases. Water the tree during prolonged dry periods and fertilize when necessary. Poplar trees growing in good soil won’t need fertilizer every year, but if the stems add fewer than six inches (15 cm.) of new growth in spring and the leaves look smaller and paler than last year, it’s a good idea to go ahead and fertilize.

Poplar tree cankers are caused by fungi that enter through injuries. Take care when performing landscape maintenance so that you don’t damage the bark with a string trimmer or hit the tree with flying debris from a lawn mower. Broken branches should be pruned to eliminate ragged edges. Prune to shape the tree while the tree is young to keep pruning wounds small.

Early detection of cankers on poplar trees might make it possible to treat a tree and keep it alive for many years. Remove branches with cankers to prevent spread of the disease. Fertilize infected trees annually in spring and water often enough to keep the soil moist to a depth of six inches (15 cm.). Good care goes a long way toward extending the life of your tree.

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The Korqin desert region of China is characterized by sand dunes, sand belts, swamps, and lakes. The climate is continental, having an annual mean temperature of 6°C. and ranges from a low of about -30°C in January to + 10°C in July-August. Annual precipitation ranges from 350 to 550 mm. 70 percent of which occurs during July – September. Evaporation from winds is very high, particularly in spring and fall. when velocities reach between 18

35 m sec. There are an average of 8 severe sand storms per year. All of these factors combine to create an environment that is very hostile for the cultivation of trees.

About 6 million hm 2 are estimated to be suitable for forestry development if appropriate tree species are planted. and if insects and pathogens do not adversely affect management. Many native and hybrid species of poplar (Populus) have been planted successfully throughout the region. Many pathogens of poplar are indigenous to the region, but presently none appear to threaten its cultivation.

The environmental conditions that make cultivation of trees difficult also are not conducive to the development of most tree leaf diseases. High winds and evaporation in spring in particular, create conditions of low humidity that prevent the formation of free moisture on leaf surfaces. Moisture is necessary for the initiation of infection by foliar pathogens and the development of disease.

Stress caused by drought and frost can predispose poplar to attack by secondary pathogens that cause canker diseases. Branch dieback and subsequent infection by various pathogens will occur in early spring if plants set terminal buds too late the previous fall. Therefore it is vital to select poplar provenances that will set bud early in the fall to prevent frost damage and reduce canker diseases.

Cultural practices common to the region reduce foliar disease development in poplars. Planting trees at low density promotes the movement of air through the plantation, drying leaf surfaces, and reducing chances for development of leaf disease. Raking and disposing of fallen leaves in the dormant season reduces pathogen inoculum and prevents or delays infection the following growing season. In plantations where raking does not occur, plowing under of fallen leaves and cultivation of crops between rows of poplar also reduces the ability of pathogens to infect leaves during the growing season.

Many people harvest the lower branches of poplar in the fall for fuel and fodder. If done correctly, pruning can be beneficial by promoting good tree form, improving wood quality, and reducing disease in branches and leaves in the lower crown area. However, often pruning is done improperly, causing severe injury to tree stems, or creating branch stubs that become infected by canker pathogens. Pathogens that infect the branch stubs are a source of inoculum for the spread of disease throughout the plantation. These stubs also cause the tree to seal the branch wound very slowly. causing a reduction in wood quality and providing sites for invasion by decay organisms. Pruning wounds to the main stem are even more damaging. The wound is a site for introduction of decay and canker organisms. Once infected wood quality and tree survival are threatened. Pathogens such as Agrobacterium sp. can be spread throughout a plantation on contaminated pruning tools.

Proper pruning involves integrating knowledge of the anatomy of tree branches, the use of good pruning tools, and proper timing. Pruning cuts should be made as close to the branch collar as possible, without cutting into the collar area. This collar can be recognized as a small ridge extending from the main stem out onto the branch. The pruning cut should be made using a sharp (and preferably sanitized) cutting tool, and should be done in the dormant season. The cut should be smooth, without ragged edges or torn bark. The younger the branch is when it is pruned, the more quickly the tree will seal the pruning wound.

The major pathogens of poplar planted in the region are described in this field guide. The guide is intended to aid in the early identification of any potential threat in order to maximize management options. Recommended management strategies and other sources of information on poplars are included.

Preventative measures, or indirect controls, are preferred. To apply a direct control measure the following three criteria must be satisfied. The proposed controls must be: 1. biologically effective. 2. economically justified. and 3. environmentally friendly. It must be understood that very few tools exist for the direct control of tree diseases. Most diseases cannot be treated therapeutically. The best control is the prevention of disease. This involves the factors summarized earlier: planting a suitable clone with disease resistance in the appropriate environment. and then applying the best cultural practices to maintain tree vigor.

More than one pathogen may often be present and diagnosis may require microscopic examination. Care must be taken to find the primary cause of a disease since stressed trees often are invaded by several microorganisms.

There may be other pathogen species present in plantations not covered in this guide that could potentially cause serious disease under some conditions. In addition, more pathogenic strains of existing pathogens may develop, Pathogens from outside the region may become established if infected plant material is introduced into an area. Implementing vigilant quarantine measures and good cultural practices will reduce the chances of this happening.

Hypoxylon Canker Fungus

Although it attacks several willow, poplar and aspen species, the Hypoxylon mammatum canker fungus most frequently targets quaking aspens growing east of the Great Plains. This opportunistic disease strikes aspens of all sizes, infecting them through wounds, insect damage or dying twigs. Air currents carry its spores to vulnerable aspen tissue. In moist conditions, they germinate and expand into healthy bark. Because infected aspens remain asymptomatic for up to two years, the disease usually takes gardeners by surprise.

Reports on Plant Diseases

Cytospora canker of poplars–including aspens and cottonwoods–and willows is caused by the fungus Cytospora chrysosperma (perfect or teleomorph state Valsa sordida). Cytospora canker has been associated with the decline and/or death of many thousands of valuable ornamental trees in landscape, windbreak, and recreational areas as well as poplar (cottonwood) cuttings in storage and nursery propagation beds.

This stem disease commonly kills Lombardy poplars (Populus nigra cv. ‘Italica') by the time they are 10 to 15 years old (Figure 1). The Cytospora fungus has been reported on a number of hosts (Table 1).

The disease is usually associated with trees growing outside their normal range or under unfavorable conditions due to a poor site, frost damage, periods of drought, extremely cold winter weather, transplant shock, or severe pruning (pollarding). The fungus kills areas of bark on branches and trunks creating circular to oval or elongate sunken lesions (cankers) (Figures 2 and 3). Frequently, as the lesions enlarge, affected stems are girdled and the portion beyond the canker is killed (Figure 1).

Figure 1. Lombardy poplar trees being killed by Cytospora canker.


Discrete cankers first appear on young trees as brown, slightly sunken areas in the smooth bark of branches and trunks (Figure 3, left). These cankers are circular to oval or irregular in shape. Frequently, as the canker gradually enlarges, affected stems are girdled and killed. Twigs commonly die without the formation of typical lesions. Vertical cracks within the lesion and along the canker margins often occur in the bark (Figures 2 and 3, right). As the cankers enlarge the diseased outer bark may become black, brown, gray, reddish brown or yellow and sunken depending on the host species and stage of disease development. The inner bark turns black and sometimes gives off a foul salty odor. The sapwood appears reddish brown to black and water-soaked. Cankers frequently start at wounds or branch stubs or at the base of dead twigs. Cankers on large stems with thick, rough bark may be imperceptible except for yellowish to reddish brown spore horns (sticky, thread-like masses of spores) protruding from bark fissures (Figure 3, right).

Highly susceptible trees, such as Lombardy poplars (Figure 1), may die within 2 to 5 years after becoming infected. Severely infected trees usually die branch by branch often producing sprouts at the base of the trunk which also become infected and die.

Cytospora chrysosperma is also the primary cause of blackstem disease of cottonwood seedlings and cuttings which causes severe losses in nursery beds and in prolonged or improper storage. Symptoms of blackstem occur in the fall as small lesions at the ends of cuttings or at leaf scars and lenticels, usually on stems but occasionally on the roots. The lesions enlarge during the winter, becoming dark brown to black and water-soaked with distinct margins.

Figure 2. Cytospora cankers on a Simon poplar in a nursery. Note the sunken girdling cankers on the branches and trunk and the flow of gum oozing from the dead tissues (Illinois Natural History Survey photo).

Disease Cycle

Cytospora chrysospermaand its perfect state Valsa sordida is generally considered to be a saprophyte or weak parasite living on dead bark. It can assume a parasitic role and quickly attack trees that have been weakened by stresses such as crowding, drought, extreme heat or cold, nutrient imbalance, transplant shock, severe pruning, fire, sunscald injury, frost, insect or mechanical injury, herbicide damage, root-feeding nematodes, insect damage, or infection by other pathogenic fungi. This opportunistic fungus often inhabits apparently healthy bark and buds and is thus in position to infect weakened tissue quickly and massively. A canker frequently begins at a wound, branch stub, or leaf scar.

Shortly after the bark dies two types of black, pinhead-sized, spore-producing bodies form in stromata in the outer diseased bark (Figure 2 and 3) the pycnidia of the asexual phase (Cytospora chrysospermai) and the perithecia of the sexual state (Valsa sordida) (Figure 4). The pycnidia are much more abundant than the perithecia. The stromata are shaped like short cones with flattened, gray-brown to black tips that break through the bark surface as small dark pimples or pustules (Figure 3). The pycnidia, under warm moist conditions, absorb water and swell, exuding long, thin, coiled, thread-like tendrils of microscopic spores, called spore horns. The yellowish to reddish brown spore horns consist of masses of one-celled spores (conidia) in a gelatinous matrix. As these structures dry, the conidia are released and are carried by dripping and splashing rain, wind, insects, birds, and tree workers' hands, clothing, and pruning tools to other trees.

The perithecia of Valsa sordida form in the same stromata with pycnidia or in new stromata beginning in autumn and winter after the formation of pycnidia. The perithecia are black, spherical, and several are arranged in a ring in the lower, outer part of the stroma. Their long necks converge to form a circle of openings in a disc which protrudes through the cracked bark (Figure 4a and b). When the stromata are wet for a prolonged period the asci (Figure 4c), each containing 8 ascospores, may exude from the perithecium much like the release of conidia. The colorless, one-celled ascospores (Figure 4d) may also be forcibly expelled into the air when the stromata in dry bark become saturated with water.

The Cytospora (Valsa) fungus overwinters as mycelia and conidia or ascospores in diseased bark and wood. Infection usually occurs through bark wounds typically resulting from mechanical damage. The fungus grows through the bark cells and the outer few rings of wood. Cankers usually develop in the fall, winter, and early spring and enlarge slowly at low temperatures (36 to 50 F or 2 to 10 C) and up to 40 millimeters per day at higher temperatures (68 to 86 F or 20 to 30 C). Bark susceptibility may be induced by heating to approximately 104 F (40 C) which is not uncommon on hot summer days. Rapid temperature shifts in the fall and spring between warm and subfreezing also predispose the bark to infection.

Figure 3. Cytospora canker of willow. Left, canker on a dwarf arctic willow stem following transplant shock (courtesy Dr. D.F. Schoeneweiss) right, cankers on an older weeping willow 9courtesy Dr. L.E. Dickens). Note the fruiting bodies of the Cytospora fungus which appear as pustules in the diseased bark.

Figure 4. Cytospora chrysosperma (left) as it would be seen under a high-power microscope. A, Section through a pycnidial stroma showing two chambers and a pore releasing spores (conidia) from the right chamber B, section of the pycnidial wall showing conidiophores bearing conidia at their tips C, six colorless, one-celled conidia. Valsa sordida (right). A. Top view of four perithecial stromata erupting through the bark B, section through a stroma showing four perithecia with the tips of their necks protruding from the stroma C, an ascus with 8 ascospores D, two ascospores. (Drawing by Lenore Gray).


A. General Control Measures

  1. Grow varieties of poplars and willows that are well adapted to the area and planting site. Select only vigorous, disease-free nursery stock. Avoid planting susceptible varieties such as Lombardy, Simon and Siouxland poplars. Instead, grow one of the resistant varieties now available. Black and peach willows are reported as being resistant.
  1. Remove all dead and dying branches on affected trees. If cankers are confined to twigs or branches, diseased bark and discolored wood may be removed with a sharp knife by cutting back 1 to 2 inches into surrounding live, healthy tissues. Whenever possible, the wound should be shaped into a vertical oval or ellipse with rounded ends. Avoid leaving branch stubs. Do not prune or work around trees when the bark is wet as this helps to spread the fungus. Pruning tools should be sterilized between cuts by swabbing them with 70 percent rubbing alcohol or fresh household liquid bleach (1 part of bleach to 9 parts of water). Remove and burn or bury all affected parts as soon as possible. Severely cankered trees cannot be restored to good health and should be cut down and burned because they are a source of infection for other trees.
  1. Some trunk cankers, if less than halfway around the stem, can be successfully removed by careful surgery of all diseased bark and the underlying discolored wood. This work is best done by a licensed and experienced arborist.
  1. Treat all bark and wood injuries promptly. Cut away all loose or discolored bark. Clean, smooth, and shape the wood into an oval or ellipse with rounded tips and its long axis oriented vertically. Swab the wound surface liberally with shellac or 70 percent alchohol. Many arborists then coat the wound with a tree wound dressing or paint. The use of commercial tree paints is not generally recommended as their effect is largely cosmetic. Surgery may prolong the lives of some severely affected trees.
  1. Keep plants growing vigorously by (a) proper applications of a balanced fertilizer in mid to late autumn or early spring based on a soil test (b) watering deeply (soil moist 10 to 12 inches deep) during hot, dry weather (repeat at 10-day intervals as long as the drought continues) (c) proper pruning and (d) winter protection of young tree trunks using strips of burlap or special tree wrapping paper to prevent sunscald and bark injury.
  1. Avoid all unnecessary bark wounds. Keep the trunk base as dry as possible and free of grass, weeds, or other debris that might attract rodents.
  1. Avoid chemical injuries. Apply herbicides and other pesticides, salt, fertilizers, and other chemicals strictly according to label directions.
  1. No chemical treatment has been shown to prevent or arrest the development of cytospora canker on poplars and willows.

B. Disease Prevention in Nurseries and in Storage

  1. Cytospora canker is common in cottonwood propagation blocks in nurseries. The disease appears to increase with the age of the blocks. It is suggested that propagation blocks not be used for more than a 4- or 5-year period2.
  1. All infected nursery stock, cuttings, and propagation material should be destroyed by burning to avoid introduction of the disease through commercial channels.
  1. Precautions should be taken to prevent excessive moisture loss in nursery material during storage. Select scion wood of high moisture content.
  1. Storage temperatures should be maintained above freezing and as close to 35 F (1 C) as possible with high humidity (95 to 98 percent) but without water forming on plant material and the walls, ceiling, or floor of the storage area.

Many factors affect seed quality. Seedborne fungi, insect damage, adverse weather (such as frost), improper storage, and physiological aging all reduce seed vigor and viability. Any rough or excessive handling of dry or moist seeds at harvest or planting can cause cracked seedcoats and kill seed embryos. These cracks may be microscopic, but they still can increase seed rot by allowing nutrients to escape and by providing an entry for soil-inhabiting and/or seed-rotting fungi.

Pod and stem blight and seed decay, both caused by fungi of the Diaporthe/Phomopsis complex, are the major problems of soybean seed grown in Illinois and elsewhere in the Midwest (Figure 2). Decayed seeds are elongated, shriveled, discolored, and often covered with white mold growth (Figure 3). Healthy appearing, symptomless seeds also may be infected and can develop into blighted or infected seedlings. Seed decay is most severe when the crop has matured under high rainfall and humidity and when harvest has been delayed by wet weather. Seedlots with 20 to 40 percent of the seeds decayed by Phomopsis spp. are not uncommon in years when weather has favored an epidemic.

For further information concerning diseases of crucifers and other vegetables, contact Mohammad Babadoost, Extension Specialist in Fruit and Vegetable Diseases, Department of Crop Sciences, University of Illinois at Urbana-Champaign.

University of Illinois Extension provides equal opportunities in programs and employment.

How to Manage Pests

Cytospora canker—Cytospora spp.

Cytospora canker affects many plants, including birch, ceanothus, cypress (Italian, Leyland, and Monterey), fir, maple, poplar, redbud, stone fruits, and willow.


Cankers on major branches commonly appear as slightly sunken, smooth, roughly elliptical, reddish brown areas and sometimes exude copious resin. On poplar, C. chrysosperma causes sunken lesions that kill many small branches and twigs without forming any definite canker. Infected branches can turn brick-red in the spring, then fade to brown or tan by the fall.

There are many other common causes of cankers, including other species of canker fungi.

Life cycle

During moist weather, minute pimplelike or warty fungal fruiting bodies (pycnidia) may develop in infected bark. Pycnidia produce yellow to red tendrils, which are strings of asexual spores (conidia). When wet, huge numbers of conidia are released and dispersed primarily by wind and splashing rain.


Drought stress and other disorders or pest damage dramatically increase most hosts' susceptibility to Cytospora canker. Provide appropriate soil moisture for species adapted to summer rainfall or riverbank environments if they are planted where summer drought prevails irrigation should generally be deep and infrequent.

Avoid planting susceptible cypress in warm areas. Grow species that are resistant or not susceptible. Poplar hybrids that show some resistance to Cytospora include Easter, Mighty Mo, Nor, and Platte.

If cankers are limited to one or a few limbs, during the growing season, remove (cut out) cankers and destroy dead or damaged wood. Pruning during the growing season allows you to better identify branches with cankers. To ensure that all the disease is removed, cut several inches to one foot below any canker symptoms into healthy wood. Check the cut surface of damaged limbs to ensure that all the disease has been removed. Incomplete canker removal wastes time and is little to no benefit in disease management.

Cytospora canker on corkscrew willow

Cytospora canker pycnidia (white) and spore masses (amber)

Cankered wood (top) incompletely pruned off

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

How to Manage Pests

Willow—Salix spp.* Family Salicaceae (Willow family)

Plant identification

Willows are deciduous trees or shrubs with invasive roots. The weeping willow is most common shrub types are used more for their colorful buds or catkins, stems, or contorted shape.

*Some species of Salix are invasive weeds. Other types of plants may be better choices when planting.

Optimum conditions for growth

Willows do best in full sun with ample water. They can tolerate almost any soil type and any climate zone.

Weeping willow
Willow foliage (top right)


Invertebrates (cont.)

  • Poplar and willow borer
  • Psyllids
  • Roundheaded borers
    • Poplar borer
  • Soft scales
    • Brown soft scale
    • Cottony maple scale
  • Spider mites
  • True bugs
    • Lace bug
  • Whiteflies
    • Giant whitefly
    • Silverleaf whitefly


  • Bacterial blight
  • Canker diseases
  • Crown gall
  • Leaf spot diseases
    • Gray scab
    • Leaf and twig spots
    • Marssonia spot
    • Tar spot
  • Powdery mildew
  • Root and crown rots
  • Rusts
  • Scab
  • Slime flux
  • Wood decay

Environmental disorders



Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2017 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California


Preventing cankers means growing vigorous trees that can fight off the entrance of pathogens into the bark by using a good tree management program. You must be faithful to your tree by using correct pruning methods, taking care not to over-fertilize and prevent defoliation of your tree by disease and insects.

Wounds are essential for most canker infections to take hold and spread, so avoid wounds, especially where active spore-spreading cankers are present. Make sure that your tree has adequate water and avoid mechanical injury to roots and trunk.

When planting a new tree: Plant your tree on a good site, use vigorous planting stock, fertilize trees to promote growth and control weeds for several years after planting. Landscape trees will benefit by deep watering or trickle irrigation, especially during dry summer months. Also maintain good drainage.

Managing leaf spot diseases

Leaf spot diseases will not seriously harm your plants, but there are things you can do that when done together, can reduce the disease on the tree in following years.

  • Rake up and destroy fallen leaves before the first snowfall to eliminate locations where diseases can survive to re-infect the plant the following growing season.
  • Do not overcrowd plants — use size at maturity as a spacing guide when planting.
  • Prune trees or shrubs to increase light penetration and improve air circulation throughout the canopy.
  • Wet conditions promote disease, so water trees at the base and be careful not to splash water on leaves. A drip or soaker hose works best for this. Avoid sprinklers.
  • Reduce stress to your tree:
    • Water your tree throughout the growing season so that the top 6 to 8 inches of the soil is moist, especially during dry summer periods.
      • Soil should be allowed to dry before watering again.
    • Maintain a 3- to 4-inch-deep layer of mulch around your tree.
      • Do not mound the mulch around the trunk of the tree but lay a flat layer with at least a 2-inch space between the mulch and stem to allow for air movement.
      • Annually reapply mulch and inspect to ensure levels are maintained.
  • Do not fertilize trees and shrubs suffering from leaf spot diseases, unless it is recommended by a soil test to correct a nutrient deficiency.
  • Fungicides are not necessary unless a tree has lost all of its leaves several years in a row.
  • Fungicides are protective and need to be applied before symptoms appear on the leaves.
    • Proper timing of fungicide applications can vary depending on the biology of the disease.
    • High-pressure spraying equipment is needed in order to get complete coverage of the canopy of large trees.
    • Hire a professional arborist to treat leaf spot diseases in large trees.

Watch the video: Apple Tree Canker Removal And Prevention Best Methods