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Ministry of Agriculture, Food and Rural Affairs

Perennial Canker

Cankers are elliptical, exude amber gum A dead twig or branch will be covered with pinhead-sized, black pimples that break through the bark. Infected branches will wilt and die. Infected twigs turn brown and eventually gray. Small black fruiting bodies form in the dead tissues. Note the cankered area on the lower portion of this trunk. This infected peach twig has numerous dark pycnidia of the fungus. Apples also get Cytospora canker.
Click to enlarge.

Beginner

This pest affects:

Peach Apricot Plum Sweet Cherry Tart Cherry  

Scientific Name
Leucostoma cincta & Leucostoma persoonii

Identification
Twigs

  • Small, sunken discoloured areas, often with alternation zonation lines
  • Diseased sapwood beneath the canker turns reddish-brown
  • Usually around winter-killed buds or leaf scars from the previous year’s foliage
  • Dead twigs and branches are usually covered with a multitude of pin-head sized black pimples erupting through the bark
  • Orange spore masses visible with a 10X hand lens

Main trunk, branch crotches, scaffold limbs, and older branches

  • Canker development may progress down the twigs into scaffold limbs where large, diffuse cankers are formed
  • First visible symptom is the exudation of gum at the point of infection
  • Copious quantity of amber-coloured gum, becoming dark brown as canker ages
  • Canker starts from a small necrotic center that slowly enlarges with the collapse of the inner bark tissue. The outer bark usually remains intact except at the points of infection
  • Infected bark dries out and cracks open, exposing blackened tissue beneath
  • Elliptical sunken cankers along the length of the trunk or limb surrounded by a series of callus rings
  • Affected limbs become progressively more girdled, lose their vigour, and the portion of the branch beyond the canker eventually die

Often Confused With
Black knot – corky, black galls; most frequently found on sour cherry and plum but can occur on other stone fruit

Bacterial canker on sweet cherry – foliar lesions and shotholes; no rings of callus surrounding cankers

Peach tree borer – larvae or pupae may be present; masses of gummy sap mixed with frass exuding from entry and exit holes

Herbicide injury – no rings of callus and peeling black bark

Southwest injury– no rings of callus; injury on south to southwest side of trunk

Mechanical injury – history of recent operations in the orchard

Period of Activity
Whenever weather conditions become humid and temperatures are above freezing during the dormant period. Early spring (pruning cuts, winter injury) and autumn (leaf scars) are probably the most important periods for infection.

Scouting Notes
After shuck fall, monitor all trees in the orchard for cankers. Cankers can be very small or can girdle the entire limb or trunk. Monitoring for and removal of cankers is best done at the same time.  Remove cankers surgically if possible or prune out the entire diseased area.

Threshold
No established thresholds.

Photo source:

Advanced

This pest affects:

 

Scientific Name
Leucostoma cincta & Leucostoma persoonii

Identification
Twigs

  • Small, sunken discoloured areas, often with alternation zonation lines
  • Diseased sapwood beneath the canker turns reddish-brown
  • Usually around winter-killed buds or leaf scars from the previous year’s foliage
  • Dead twigs and branches are usually covered with a multitude of pin-head sized black pimples erupting through the bark
  • Orange spore masses visible with a 10X hand lens

Main trunk, branch crotches, scaffold limbs, and older branches

  • Canker development may progress down the twigs into scaffold limbs where large, diffuse cankers are formed
  • First visible symptom is the exudation of gum at the point of infection
  • Copious quantity of amber-coloured gum, becoming dark brown as canker ages
  • Canker starts from a small necrotic center that slowly enlarges with the collapse of the inner bark tissue. The outer bark usually remains intact except at the points of infection
  • Infected bark dries out and cracks open, exposing blackened tissue beneath
  • Elliptical sunken cankers along the length of the trunk or limb surrounded by a series of callus rings
  • Affected limbs become progressively more girdled, lose their vigour, and the portion of the branch beyond the canker eventually die

Often Confused With
Black knot – corky, black galls; most frequently found on sour cherry and plum but can occur on other stone fruit

Bacterial canker on sweet cherry – foliar lesions and shotholes; no rings of callus surrounding cankers

Peach tree borer – larvae or pupae may be present; masses of gummy sap mixed with frass exuding from entry and exit holes

Herbicide injury – no rings of callus and peeling black bark

Southwest injury– no rings of callus; injury on south to southwest side of trunk

Mechanical injury – history of recent operations in the orchard

Biology
Perennial canker occurs regularly on sweet cherry, apricot, and plum trees, but is not generally as damaging on these crops.  The disease is most damaging to young orchards, where it may cause tree death. In older orchards, trees gradually lose productivity and slowly decline as individual scaffold limbs are killed.

The fungus overwinters in cankers and dead twigs. Small black fruiting bodies (pycnidia) containing spores of the fungus are produced throughout the year on the smooth bark covering diseased areas on dead wood. Spores are extruded in a gelatinous orange-yellow matrix during wet or humid weather any time the temperature is above freezing.

The Leucostoma species that attack peach and other stone fruits can not invade healthy bark. However, once inside the tree they can invade aggressively. Cankers are usually initiated in weak, dying or dead tissue or at unhealed wounds. The most common infection sites are pruning cuts, leaf scars, shade-weakened twigs in tree centres, winter-injured buds, twigs and bark, insect injuries caused by oriental fruit moth and borers and brown rot infections. Rodent damage and wounds resulting from cultivation, picking ladders, wire mouse guards, and broken limbs may also become infected. Short branch stubs left as a result of improper pruning do not heal and provide the ideal gradient of dying tissue that is readily colonized by the fungus. Pruning cuts are most susceptible to infection if they are made early in the dormant season. However, when conditions are unfavourable for normal growth activities of the tree, pruning may become infected even when pruning is done during April or May.  In older orchards most new infections are found at the nodes of previous year’s shoots, usually associated with buds or leaf scars.

The tree responds to infection by producing gum.  Once the fungi are established, they continue to grow and expand into adjacent healthy tissue. Although growth is slow, the fungi are able to continue this expansion, even at temperatures just above freezing, when tree defense responses are not active. As temperatures rise above 10°C, tree growth becomes progressively more active and a ring of callus tissue is normally formed around the canker. This defensive ring is then breached in the fall and subsequent early spring, as the dormant tree is once again unable to resist fungal advancement. Renewed tree growth eventually causes a new ring of callus to be formed, and this annual cycle of callus formation and canker expansion leads to the production of concentric callus rings around the initial infection site. Elliptical sunken cankers develop along the length of the trunk or limb because the tree establishes barriers to fungus growth more rapidly at the sides than at the end of cankers.  Where normal tree growth is restricted because of environmental stresses such as drought, callus production may be limited and cankers will appear more spread out.

Canker formation on scaffold branches inhibits movement of nutrients and water which results in symptoms of nutrient deficiencies as well as wilting and dieback of twigs on that branch. Canker development on the trunk can cause rapid death of the entire tree.

Period of Activity
Whenever weather conditions become humid and temperatures are above freezing during the dormant period. Early spring (pruning cuts, winter injury) and autumn (leaf scars) are probably the most important periods for infection.

Scouting Notes
After shuck fall, monitor all trees in the orchard for cankers. Cankers can be very small or can girdle the entire limb or trunk. Monitoring for and removal of cankers is best done at the same time.  Remove cankers surgically if possible or prune out the entire diseased area.

Threshold
No established thresholds.

Management Notes
At planting time and first year

  • Plant healthy nursery stock free of infection.
  • Select sites for new plantings with deep, well-drained soil and good air drainage to minimize the chances for winter injury.
  • Select winter hardy varieties.
  • Do not plant young trees adjacent to or down-wind from older, heavily infected peach blocks.
  • Plants trees as soon as possible after receiving them from the nursery to avoid any additional stress.
  • Prune new trees shortly after planting on warm, dry days.
  • Remove all poor angles and weak side branches.
  • Sow a cover crop (early July).
  • Protect trees from rabbits and mice.
  • Avoid any contact with herbicides on the young bark tissue.
  • Apply a fall paint to protect for southwest injury.
  • Avoid cutting into the collar area of the branch where it meets main branches or the trunk of the tree. When the collar area is injured or cut, the healing process is delayed or impaired, because wound-healing periderm tissues are located primarily in the collar region.
  • Perform surgery on younger trees during June and early July. Remove all diseased bark around the canker and about 3-5 cm of healthy tissue from around the sides and ends, respectively. The resulting wound, when finished, should have a smooth margin and be slightly rounded above and below to favour rapid wound closure.
  • Leave surgery sites uncovered without wound dressing. Some pruning paints seal in moisture, which prevents healing and provides an ideal environment for fungal infection.
  • Prune on warm, dry days at bloom time or shortly after.
  • Remove all dead wood and poorly angled-branches.
General recommendations:
  • Apply nitrogen fertilizers early (March, April) to bearing trees or consider split applications for nitrogen in spring and early summer.
  • Avoid late applications of manure.
  • In June, remove dead wood and lightly thin out new growth.
  • Manage oriental fruit moth, peachtree borers, plant bugs and brown rot.
  • Protect trees from rabbits and mice.
  • Re-apply a fall paint to protect against southwest injury until the tree is five years old.

Some of the information above is excerpted from:

Photo source: