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for Bacterial Canker

Widely distributed throughout the United States, bacterial canker is most common on cherries and plums, but may also affect apricots, peaches and many other kinds of stone fruits. Suspect this plant disease if sunken, water-soaked or “gummy” lesions form on the trunk or twigs. When trees begin active growth in the spring, a sour smelling sap may ooze from these wounded areas. The cankers become darker than the surrounding healthy bark, and the underlying tissue is reddish-brown to black and moist.

Note: If cankers girdle the branches or trunk, the leaves above the diseased area curl and turn yellow. Growth stops and the branch or tree will eventually die.

The bacterium that causes canker, Pseudomonas syringae, enters trees through injured bark or an existing wound, such as a pruning cut on a twig or branch. Frost damage in the spring may promote additional infections. Bacterial canker infections occur during fall, winter and early spring (during cool, wet weather) and are spread by rain or water, and pruning tools. The bacteria overwinter in active cankers, in infected buds and on the surface of infected and healthy trees and weeds.

  1. Prune flowering trees during blooming when wounds heal fastest.
  2. Remove wilted or dead limbs well below infected areas.
  3. Avoid pruning in early spring and fall when bacteria are most active.
  4. Treat all pruning cuts immediately with Tanglefoot® Tree Pruning Sealer and make sure to disinfect your pruning equipment — one part bleach to 4 parts water — after each cut.
  5. If using string trimmers around the base of trees avoid damaging bark with breathable Tree Wrap to prevent infection.
  6. Brush bark with white latex paint diluted with water to reduce bark-damaging temperature fluctuations.
  7. Research has shown that copper fungicides have some success against this stone fruit problem. However, results are inconsistent. We recommend using it as one part of a total management program.
  8. Remove weeds and grass from around the base of young trees to improve air circulation and keep the trunk and crown dry.
  9. Organocide® Plant Doctor is an earth-friendly systemic fungicide that works its way through the entire plant to combat a large number of diseases on ornamentals, turf, fruit and more. Mix 1/3 to 3/4 oz per gallon of water and paint or spray over pruning wounds and surrounding areas.

Colorado State University

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by W.R. Jacobi* (12/13)

Quick Facts…

Figure 1: Orange discoloration found in spring and early summer associated with cytospora canker.

Figure 2: Cytospora canker on three branches, each with scattered pycnidia.

Figure 3: Orange spores oozing from pycnidia.

  • Cytospora canker is caused by several species of Cytospora (sexual form Valsa and Leucostoma) fungi. The name comes from the asexual stage of the pathogen that is more commonly seen.
  • The disease occurs on woody shrubs and trees or parts of plants that are slightly stressed.
  • Many trees and shrubs are affected by this disease (apple, ash, aspen, birch, cottonwood, elm, maple, peach, spruce, willow).
  • The canker-causing fungi cause girdling of the plant, killing the plant above the canker.
  • To manage the disease, reduce stress on trees, use resistant plants, remove infected limbs, clean wounds and prune properly.

Cytospora canker is caused by various species of the fungus Cytospora (sexual genera of Valsa and Leucostoma). These pathogens affect many species of shrubs and trees in Colorado, including aspen, cottonwood, lombardy and other poplars, apple, cherry, peach, plum, birch, willow, honeylocust, mountain ash, silver maple, spruce, and Siberian elm. Some Cytospora species are host-specific while other species can infect several different tree species. For example, willow, cottonwoods, and aspen are susceptible to one species. The fungus attacks trees or parts of trees that are injured or in a weak or stressed condition. The fungus grows in the living bark (phloem) and wood (xylem) and kills by girdling the branch or tree. The fungus can attack tree bark during the fall-winter spring seasons when temperatures are warm but the tree is dormant and cannot defend itself. Trees affected by drought, late spring frosts, insect and fungi defoliation, sunscald, herbicides, or mechanical injury are susceptible to Cytospora infection. The disease especially affects trees with root damage, which are often found in areas under construction, or trees that recently have been transplanted. Stands of aspen that have been thinned and young aspen sprout stands may suffer from Cytospora canker.

Sexual and asexual spores of Cytospora species infect freshly wounded tissue. The spores are released after fruiting bodies have absorbed water during rain events. Conidia ooze out of the wet fruiting bodies and are dispersed by rain splash and blown by wind. Many times fruiting bodies are not formed since the cankered tissue dries out too rapidly in the dry western climates.


Cytospora species cause branch dieback and cankers on trees or shrubs. Cankers on stems and branches are often elongate, slightly sunken, discolored areas in the bark. Many times, however, the discoloration is not evident because the fungus killed the bark rapidly. The fungus grows so fast on stressed trees that there is no evidence of a sunken canker. Bark often splits along the canker margin as the tree is defending itself and callus formation occurs. The fungus may quickly girdle and kill twigs without forming cankers. Symptoms vary with host species affected and stage of disease development. Bark above infected cambium may appear sunken and yellow, brown, reddish-brown, gray, or black. Diseased inner-bark and cambium turns reddish-brown to black, and becomes watery and odorous as it deteriorates. Wood below the cambium is stained brown (Figure 1). Liquid ooze on aspen and gummy ooze on peach and cherry are common. Cankers, sunken dead areas of bark with black pinhead-sized speckling or pimples, may be evident (Figure 2). The pimples are the reproductive structures of the fungus. Under moist conditions, masses of spores (seeds) may ooze out of the pimples in long, orange, coiled, thread-like spore tendrils (Figure 3). Reddish-brown discoloration of the wood and inner bark also may be evident. Dead bark may remain attached to the tree for several years, and then fall off in large pieces.

On spruce trees, the disease appears as sunken, resinous areas surrounded by swollen callus, giving a gall-like appearance. Small black fruiting bodies may occur on the canker. Once the branch is girdled, needles may yellow or redden. The branch eventually dies. Large amounts of resin flow from infected areas, coating branches and stems. Unless you see sunken areas surrounded by swollen callus, resin flow on spruce may indicate that other stresses, diseases or insects are affecting the tree.


Because this canker disease usually occurs on a weakened host, the primary method of control is to prevent stress on the tree. Drought and oxygen starvation of roots by flooding soil with water are the two most common stresses that predispose trees to Cytospora infection. High temperatures seem to be related to Cytospora canker on our local alders.

To help a tree resist infection, prepare soil before planting, fertilize, water properly for winter and summer, prune, and avoid injury to the trunk and limbs. Proper care of recently transplanted trees also is essential to avoid stress and infection. See fact sheets 2.932, Environmental Disorders of Woody Plants, 7.211, Fall and Winter Watering, and GardenNotes 635, Care of Recently Planted Trees.

Wounds caused by lawnmowers and weed trimmers are prime targets for infection on trees in landscaped areas. Insects, such as oystershell scale, stress the tree and predispose it to Cytospora infection. Insects should be controlled to prevent mortality by the combined stress of the insects and Cytospora canker.

Help prevent cankers at pruning wounds on peach and cherry trees by applying labeled fungicides as wound dressings. Do not rely on the effectiveness of fungicides on wounds of other trees to prevent infection.

Another way to prevent Cytospora damage is to use species or varieties well adapted to the planting site conditions. These cultivars will be more likely able to resist the disease. Purchasing healthy nursery stock will decrease the possibility of infection. Once infection occurs, the best treatment is to increase plant vigor and sanitation. Remove all infected limbs and other areas. When removing branches, arborists and homeowners should make a smooth cut at the base of the limb, as near the trunk as possible, without damaging the branch collar (swollen area at base of branch). Jagged and rough cut surfaces promote infection. Once infection occurs, the best treatment is to increase plant vigor and sanitation. Remove all infected limbs and other areas. Clean wounds to avoid further spread of infection. Remove dead bark to dry out the diseased area and help the tree defend itself against insect and fungal attacks on the cankered area. Directions for proper wound and canker treatment are as follows:

  • Prune or cut trees only during dry weather.
  • Clean tools and wipe them with ethyl alcohol, Lysol or other disinfectant. Clorox may be used at a concentration of one part Clorox to nine parts water.
  • If a wound is fresh (one month old or less), use a sharp knife to carefully cut and remove all injured or diseased bark back to live, healthy tissue. If the wound is older, just remove loose bark pieces. It is important not to cut, remove or damage callus that may be forming at the canker edge. Callus will look like swollen bark growing across the dead area. Scrape the wound surface clean of loose bark.
  • Clean tools and disinfect after each cut.
  • Cleaned wounds should not have any sharp angles.
  • Do not apply any tar, oil-based paint or other wound dressing. The best method to prevent infection or decay is to allow the cleaned tissue to dry out.
Table 1: Some resistant species and cultivars.
Ash Most cultivars.
Aspen Resistant cultivars not commercially available.
Cottonwood Cultivars: Noreaster, Platte, Mighty Mo, Ohio Red. Avoid Lombardy, Bolleana, Sioux Land.
Elms Most cultivars
Hackberry Most cultivars
Honeylocust Most cultivars.
Junipers Most cultivars.
Lindens Big and little leaf.
Maples Most species and cultivars.
Pines Most species and cultivars.

1Colorado State University professor, bioagricultural sciences and pest management. 9/99. Revised 12/13.

Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.

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Cankers On Trees: How Do You Treat Cankers In A Tree

You may have noticed some unsightly cankerous looking wounds in your tree. What are tree cankers and what causes them, and how do you treat cankers in a tree once you see them? Continue reading to learn more about the types of canker in trees and how to go about preventing tree cankers.

What are Tree Cankers?

Cankers on trees appear as isolated dead areas on the bark, stems, branches or twigs. Cankers may appear as discolored areas or depressed places on the bark.

A fungus that enters the tree and grows between the bark and the wood killing the bark generally causes cankers. However, cankers can also be caused by damage from weed eaters, lawnmowers, chemicals, insects or environmental conditions.

The canker itself makes the tree highly vulnerable to bacteria, fungus and insects. Young fruit trees have an especially difficult time recovering from cankers. Established shade trees may weaken and become susceptible to wind damage.

The healthier the tree is, the more likely it is to ward off serious damage from a canker disease. Trees that are weakened by temperature, drought, poor nutrition or other present diseases are much more susceptible to canker diseases. Canker diseases are more common with hardwood trees than on conifers.

Type of Cankers in Trees Vary

Depending on the region where you live, different cankers on trees are found. Some of the more common types of canker in trees include:

  • Thyronectria canker is caused by a fungus and is most common on the honey locust tree.
  • Nectria canker tends to attack deciduous shade trees, crabapples and pears.
  • Cytospora canker is found most often in fruit trees, hardwood forest trees and shrubs, as well as over 70 species of conifers.
  • Hypoxylon canker is seen in different species of oak, including red and white.

How Do You Treat Cankers in a Tree Effectively?

So how do you treat cankers in a tree? Preventing tree cankers is the best method of protection. It is best to plant native or well-adapted species for your growing region. These tree species will suffer less stress and adapt well to the soil type, sun exposure and overall environmental conditions in your area.

The avoidance of stress is the best and most effective protection against canker diseases. Proper tree care including watering, feeding, mulching and pruning will help to keep trees as healthy as possible.

Once a tree has canker, it is essential to remove as much of the canker fungi as possible from the tree to avoid infection and spread. Prune only during dry weather and make cuts with a sterilized cutting tool at least 4 inches (10 cm.) below the edge of the canker on trees.

Canker diseases on shade and forest trees: Part 1

In addition to foliage and root diseases, canker disease pathogens can attack tree trunks and branches. Cankers are usually fungal, but can be caused by bacteria as well. Some well-known examples include: chestnut blight, Phomopsis canker of juniper, beech bark disease and thousand canker disease of walnut.

Cankers are essentially “sores” that erupt on the branch or trunk of a tree and kill woody cell tissue in a localized area. Typically, cankers are described as “sunken areas” that protrude through broken or blistered bark. Some cankers (such as cacterial canker of cherry) are very noticeable – which is typical of perennial or target cankers.

Other types of cankers (such as chestnut blight) are much harder to spot (referred to as diffuse cankers), because they do not create the ridges of callus around the typical target canker.

Bacterial Canker of Cherry | Photo by MSU Extension

Chestnut Blight Canker | Photo by State University of New York College of Enviornmental Science & Forestry

Cankers often enter a tree via openings in the bark caused by natural or manmade wounds. Lawn mowers, weed trimmers or weather-related damaged (hail, wind, etc.) are all good examples of injuries that can occur. Once inside the tree, cankers can burst through at any spot as the pathogen moves through the tree’s tissues.

Depending on the type of canker, their size and shape can vary. However, cankers often start as small lesions and grow larger over time. As they grow, they can kill the water conducting (xylem) and food conducting (phloem) systems of a tree branch resulting in stunted, off-color or dead foliage. And if the canker spread, it can possibly move to kill other limbs or even the entire tree.

Cankers are very difficult to treat and there may not be a suitable chemical treatment available. Trees that are stressed may be more susceptible to attack and because no viable chemical treatment is available, increasing tree vigor through fertilization and watering are often recommended. Improved tree vigor will often help improve the tree’s condition but may not be a total cure for the problem.

In part two of this article, some specific canker diseases will be discussed and how Michigan residents can help be on the lookout for canker-related issues. Through programming offered by Michigan State University Extension, such as the Eyes on the Forest and Sentinel Tree Network, volunteers can help be on the lookout for many different types of tree problems.

Botryosphaeria Canker

Botryosphaeria canker is an important disease of many landscape and forest trees and shrubs. To date, there are more than two dozen genera in the order Botryosphaeriales that were previously described simply as Botryosphaeria. Some of these genera are known to green industry professionals, such as Diplodia and Sphaeropsis, while many are not. Much remains to be understood about many of these genera and whether they occur on woody plants in southern New England. Therefore, for the purpose of this fact sheet they will be collectively referred to as Botryosphaeria sensu lato (s.l.).


Due to the tremendous diversity of genera and species in Botryosphaeria s.l., hundreds of woody plants are susceptible to infection, especially when plant vigor is low. Recent research has shown that few species of Botryosphaeria s.l. are host-specific, meaning that many are capable of attacking a wide array of trees and shrubs. However, the most commonly afflicted plants on the landscape in our region include apple/crabapple, cherry, dogwood, honeylocust, elm, oak, ash, holly/inkberry, maple, pine, spruce, hemlock and rhododendron/azalea.

Symptoms & Disease Cycle

The cambium and sapwood of weakened trees are vulnerable to extensive cankers that disrupt or cease transport of water and minerals beyond the infection site. Typical symptoms are the sudden browning of leaves during the growing season or failure to leaf out in the spring. However, symptoms can be highly variable depending on the host and predisposing stresses present. The extent of Botryosphaeria canker infections can range from small areas of necrotic bark to girdled shoots and branches to extensive cambial death spanning several feet along the trunk. When infections are severe, woody plants often produce an abundance of water sprouts from the trunk and exhibit discolored and sloughing bark. Winter injury, drought stress, repeated insect defoliation, root disease, excessive pruning and other physical wounds often predispose trees and shrubs to infection. In general, Botryosphaeria s.l. species behave as opportunistic pathogens that attack weakened and stressed hosts. In addition, many Botryosphaeria s.l. species can survive as endophytes, invading hosts and causing no observable symptoms for long periods of time until plants become stressed. These latent infections can rapidly expand to cause severe dieback on trees and shrubs suffering from transplant shock. Once established in the canopy, the fungus forms small, black-colored fruiting structures (pycnidia and/or pseudothecia) that erupt through the bark. Persistent wet weather, primarily during the spring, facilitates spore dispersal by running/splashing rainwater and wind. Other means of spore dispersal include insect feeding and the use of contaminated pruning tools. Spores will germinate and invade any wounds or natural openings present in the bark. The fungus overwinters within infected and dead branches in the canopy or those that have fallen to the ground.


As with any opportunistic pathogen, minimizing stresses that predispose woody plants to infection is critical. Avoid excessive pruning, especially on recently transplanted trees and shrubs. Irrigate on regular intervals during extended dry periods to minimize drought stress, fertilize if soil mineral levels are inadequate, maintain a layer of well-composted organic mulch over the root zone to retain soil moisture and limit mechanical wounds (e.g. string trimmers) and avoid needles branch, stem, and root damage. Regular sanitation pruning should take place, especially for trees and shrubs with thin bark (e.g. beech, Japanese maple, dogwood), to remove low-level infections that may be present in the canopy. Avoid pruning during wet periods in the spring as this is the time period when the fungus is most actively sporulating and sanitize pruning tools after working with plants known or suspected of being infected by Botryosphaeria canker.

Nectria Canker

Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Revised: 8/13/2012
Item number: XHT1094

What is Nectria canker? Nectria canker is a common and potentially lethal disease that affects many species of trees and shrubs. This disease can cause significant damage on newly planted, as well as on established, trees and shrubs that are under stress.

What does Nectria canker look like? Nectria canker is characterized by the production of sore-like wounds (cankers) that form on twigs, branches, and trunks. Cankers can form at leaf scars and wherever injuries occur. Injuries can be caused by pruning (particularly improper pruning), frost, hail, cracking from heavy snow or ice, sunscald, insects, or mammals. Cankers appear first as slightly sunken areas on the bark, but can grow for years, becoming target-shaped or elongated. Small branches girdled by cankers can wilt suddenly, fail to leaf out, and die.

Where does Nectria canker come from? Nectria canker is caused by two fungi, Nectria cinnabarina and Nectria galligena. These fungi survive in the margins of cankers where they produce numerous fruiting bodies (reproductive structures). Fruiting bodies can be cream, coral, orange, or red, and eventually darken to brown or black with age. Spores are dispersed by wind, water, and pruning tools. Cankers grow slowly, usually when the host is dormant, or under stress. Infected plants may hold the fungus in check by producing wound-closing (callus) tissue around the infected area.

How do I save a tree with Nectria canker? There is no cure for Nectria canker. Remove smaller branch cankers by pruning six to eight inches below the canker. Disinfect pruning tools after each cut by dipping them for at least 30 seconds in a 10% bleach solution or alcohol (spray disinfectants that contain at least 70% alcohol can also be used). Trees with trunk cankers may live many years with the disease. Healthy trees are better able to slow the development of Nectria canker, so make sure that trees are watered and fertilized properly.

How do I avoid problems with Nectria canker in the future? Choose plants that are well-adapted to your local climate. Avoid any stresses to your trees and shrubs. Prune properly (see UW-Garden Facts XHT1014 and XHT1015), and avoid injury to root and trunks from lawnmowers. Remove grass from around the base of trees and shrubs, mulch properly, and water as needed to avoid drought stress.

For more information on Nectria canker: See UW-Extension Bulletins A3281, A1771, A1817, A1730 and A2308 or contact your county Extension agent.


Tags: canker, disease Categories: Tree & Shrub Problems, Trees & Shrubs

Neonectria ditissima
(Nectria canker (apple, pear))

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Calcium hydroxide against apple canker (Nectria galligena)


PDF – German/Deutsch


Anwendung von 3x 50 kg/ha ungenutzte Lagerkalk (Kalziumhydroxid) in Blattfallperiode verringert die Anzahl von krebsbefallenen Zweigen im darauf folgenden Juni mit maximal 40%. Nicht oder weniger effektiv zeigte sich Baumanstrich, benutzte Lagerkalk, Landbaukalk, Schachtelhalm Tee, Mikroorganismen oder Wasserglas.

Summary translation

Apple canker is one of the most harmful diseases in organic apple growing in the Netherlands. It causes the loss of branches or whole trees and rot in apples. At present, growers aim primarily at reducing the infection pressure. Despite all the time invested in pruning out apple canker infections, many growers do not succeed in stabilising canker in their orchards. Especially where infection pressure is high, an effective preventative spray against canker would be very welcome.

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Crop husbandry > Production systems > Fruit and berries

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Bull’s-eye Rot

Fig. 3. Bull’s-eye rot on Gala. Photo by Christian Aguilar.

Bull’s-eye rot, caused by Neofabraea species, occurs both on apple and pear in the maritime Pacific Northwest. The fruit becomes susceptible to infection by the fungus in areas or years with frequent rains near or during harvest. Conidia from the cankers are the source of inoculum that causes infection. The conidia germinate on the fruit surface, and enter the apple through the lenticels (stomata) or breaks in the skin, and form appressoria, which are specialized cells that facilitates attachment and penetration of the host by the fungus. Fruit can become infected any time after bloom and susceptibility increases as the growing season progresses. Infections remain latent in the fruit and become active after 4-7 months in storage. Symptoms first appear as brown, depressed, circular spots that are flat to slightly sunken with a light brown center; spots may occur singly or be numerous (Fig. 3). As the spots extend, fungus fruiting bodies (acervuli) develop in the center, often in concentric rings giving the appearance of a bull’s eye. The fruiting bodies of the fungus are not always present. When the fruiting bodies are present, they protrude through the fruit skin as short, wet, cream-colored masses in the decayed area. The decayed tissue is somewhat mealy and firm, and does not separate easily from healthy tissue.

Several Neofabraea species can infect fruit and each species causes specific symptoms. Infections incited by Neofabraea alba develop as a soft rot with white mycelium that covers the rot, releasing white spore masses. An infection incited by Neofabraea perennans appears as circular, sunken, brown lesions and the center of the lesion is much paler than that of lesions caused by N. alba. Infections incited by Neofabraea malicorticis cause lesions that are circular, brown, and sunken with gray to cream-colored acervuli that are often apparent and concentrically arranged in the center of the lesions. The importance of the different Neofabraea species that incite bull’s-eye rot on apples is dependent on the growing region. The presence of cankers and climate of the region determine the amount of inoculum of a particular species in an orchard.

Management in orchard. Refer to canker management above.

Management in storage. Keep fruit dry after harvest and remove fruit from the orchard as soon as possible. Induce rapid cooling of fruit and store in a low oxygen atmosphere. The extent of infection can be estimated by exposing a sample of fruit to high humidity and temperatures between 64 – 70 °F for one month. Fruit with significant incidence of Bull’s-eye rot should be marketed early.
Chemical controls. Fungicides should be applied before fall rains at petal fall and pre-harvest. Refer to the Pacific Northwest Plant Disease Management Handbook for more information on pesticide use.

Chemicals available for use in Apple Orchards

Excerpt from the WSU Crop Protection Guide. For timings at which each pesticide can be used refer to the Crop Protection Guide.

Perennial Canker

Perennial canker is caused by the fungus which is closely related to the fungus causing apple anthracnose canker. It is prevalent in regions where summers are hot and dry, and winters are severe. The causal organism enters through wounds or injuries from the woolly apple aphid (Eriosoma lanigerum). As the canker develops, the host produces a raised layer of callus tissue, separating the diseased tissue from healthy tissue. As the canker enlarges, it cuts off the sap-conduction tissue, resulting in a reduction of growth and yield and sometimes death of the tree. Over time the cankers consist of a series of concentric callus rings of woody tissue encircling the wound. First-year cankers appear elliptical, sunken, and orange, purple, or brown color. The fungus survives the winter as mycelium and conidia in cankers and in infected fruit left in the orchard. Conidia are exuded from acervuli in a gelatinous matrix and dispersed by rain splash to wound sites where new infections occur. The acervuli are black and protrude through the epidermis of host tissue. Sporulation typically occurs during autumn and winter depending on the environment. The cankers enlarge in late winter and early spring. The annual reactivation of cankers depends mainly upon the presence of woolly apple aphid, which is attracted to the succulent callus tissue around the canker margins, creating wound sites where new infections can occur.

More Information

  • Hortsense website
  • Pacific Northwest Plant Disease Management Handbook


Sutton, Aldwinckle, Agnello, and Walgenbach. 2014. Anthracnose canker and perennial canker. Compendium of Apple and Pear Diseases and Pests, 2nd edition 51-53.

Use pesticides with care. Apply them only to plants, animals, or sites listed on the labels. When mixing and applying pesticides, follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. If pesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original containers and keep them out of the reach of children, pets, and livestock.

YOU ARE REQUIRED BY LAW TO FOLLOW THE LABEL. It is a legal document. Always read the label before using any pesticide. You, the grower, are responsible for safe pesticide use. Trade (brand) names are provided for your reference only. No discrimination is intended, and other pesticides with the same active ingredient may be suitable. No endorsement is implied. articles may only be republished with prior author permission © Washington State University. Republished articles with permission must include: “Originally published by Washington State Tree Fruit Extension Fruit Matters at” along with author(s) name, and a link to the original article.

Apple canker Nectria galligena

Look for

Cankers are deformed and diseased areas of tree bark. The directly infected area is usually sunken down, with the surrounding bark cracked and distorted. Initial signs of infection may include new shoots dying and wilting or discoloured leaves. Fruits can also be affected and may rot. Cankers usually have white or red coloured pustules depending on the time of year.

Plants affected

  • Apple canker infects apple, pear, mountain ash, beech, hawthorn, poplar and willow. Some varieties are more susceptible than others.

About Apple canker

  • Apple cankers occur when the fungus Nectria galligena finds its way into cracks and wounds in tree bark.
  • The infection will kill the tissue beneath the bark first.
  • The bark around the canker will eventually die back revealing the tissue.
  • Damage from pruning can also become infected.
  • Fungal spores appear creamy white in the spring and a darker red colour later in the year.
  • Spores can move between wounds by wind, water splash, or insect.
  • Wet soil exacerbates the infection.
  • Mild infections still allow some fruit to set.
  • Severe infections can rarely be cured and the tree may die.
  • The more infected and exposed areas a tree has, the more susceptible it is to further damage and infections.



Products containing the following chemical ingredients are all effective on Apple canker

  • Myclobutanil
  • Mancozeb

Note: It is important to read manufacturer’s instructions for use and the associated safety data information before applying chemical treatments.


  • Remove infected branches and twigs, making clean, neat cuts.
  • Larger cankers on trunks and thick branches can be cut out, although care must be taken to ensure that all bark showing symptoms of disease is removed.
  • Burn all removed infected material to ensure the spores are destroyed.


  • Disinfect blades before and after pruning.
  • After pruning, apply canker paint to exposed healthy tissue.
  • Try to prune only in dry weather.
  • When planting new trees, pick varieties with a higher level of resistance to canker.
  • Include a spade of lime with the soil when planting a new tree.
  • Pruning back leaves and branches to improve the air circulation of older trees will help to stop the disease establishing.

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