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Ministry of Agriculture, Food and Rural Affairs

Anthracnose canker

Anthracnose cankers begin to crack as they mature exposing long fibers which give a “fiddle string” appearance Anthracnose cankers begin to crack as they mature exposing long fibers which give a “fiddle string” appearance
Click to enlarge.

Beginner

Scientific Name
Pezicula malicortici, also known as nectria canker

Identification

  • Cankers appear as sunken lesions on limbs and trunks, surrounded by living tissue.
  • Infections from the anthracnose fungus appear in the fall as small circular reddish or purple spots that become elliptical and sunken the following spring.
  • Diseased tissue begins to crack and slough off, long fibers are exposed which give the canker a “fiddle string” appearance.
  • Cankers do not expand after the first year of infection,
  • Cankers produce spores on dead bark for several years.
  • Spores also infect fruit and develop into a bull’s-eye rot in storage.

Often Confused With

  • European canker - European canker occurs where the tree has been injured such as pruning wounds or leaf and fruit scars. Canker enlarges each year and often contains bright orange fruiting bodies during the winter. Anthracnose canker infects healthy wood and is small lesion that doesn’t grow in size and has a fiddle string appearance.
  • Fire blight canker - Fire blight canker becomes sunken with cracked margins with bacteria oozing out onto the surface of the canker. Cankers enlarge and can girdle the branch. Anthracnose canker infects healthy wood and is small lesion that doesn’t grow in size and has a fiddle string appearance.

Period of Activity
Infections occur from green tip right up to harvest during wet weather.

Scouting Notes
Monitor trees for cankers throughout the season. Mark infected trees with bright coloured flagging tape or spray paint to make it easier to find them and prune out infected limbs during the dormant season

Thresholds
 None established.

Advanced

Scientific Name
Pezicula malicortici, also known as nectria canker

Identification           
In general, canker refers to the symptom of sunken lesions on twigs, branches, crowns, stems or trunks, surrounded by living tissue. The impact of a canker on the health and productivity of a tree depends on the location, number and size of the canker. A canker on the main trunk of a tree results in the death of the tree if it expands or girdles the trunk. A canker on a branch causes the rest of the branch beyond the canker to die or become much less productive, without affecting the rest of the tree.

Anthracnose infections on limbs and trunks develop into small circular reddish or purple spots that become elliptical and sunken the following spring. As anthracnose cankers mature, cracks develop separating the diseased tissue from the healthy bark as the tree compartmentalizes the infection limiting the lesion expansion and begins to heal itself. As the diseased tissue begins to crack and slough off, long fibres are exposed which give the canker a “fiddle string” appearance. Although the anthracnose canker does not expand after the first year of infection, it can produce spores on dead bark for several years. The spores also infect fruit and develop into a bull’s-eye rot later on in storage.

Often Confused With

  • European canker - European canker occurs where the tree has been injured such as pruning wounds or leaf and fruit scars. Canker enlarges each year and often contains bright orange fruiting bodies during the winter. Anthracnose canker infects healthy wood and is small lesion that doesn’t grow in size and has a fiddle string appearance.
  • Fire blight canker - Fire blight canker becomes sunken with cracked margins with bacteria oozing out onto the surface of the canker. Cankers enlarge and can girdle the branch. Anthracnose canker infects healthy wood and is small lesion that doesn’t grow in size and has a fiddle string appearance.

Biology
 In general, cankers form when a pathogen infects and colonizes the cambium tissue under the bark of twigs, branches, trunks or crowns of trees. The cambium tissue eventually dies and the bark adjacent to the infected cambium becomes sunken, discoloured, cracked or sloughed off.

During prolonged periods of cool, wet weather in the fall, rain splashes spores from anthracnose cankers to trunk or scaffold limbs of adjacent trees where the pathogen overwinters.

Period of Activity
Infections occur from green tip up to harvest during wet weather.

Scouting Notes
Monitor trees for cankers throughout the season. Mark infected trees with bright coloured flagging tape or spray paint to make it easier to find them and prune out infected limbs during the dormant season.

Thresholds
None established.

Management Notes

  • Although fungicides reduce the spread of cankers, they are not effective at curing existing infections. It is best to prevent the establishment of cankers.
  • Keep pruning tools sharp to avoid ragged cuts or torn bark at cuts.
  • Prune during the dormant season in the winter before sap flow begins and when temperatures are too cold for the pathogen to be active. This minimizes the chance of disease organisms being spread on pruning tools.
  • Prune branches back to the collar, leaving the collar intact to heal the wound, but avoid leaving stubs.
  • Prune out all dead wood, it serves as a reservoir for the fungus.
  • Remove cankers promptly by pruning the branch several centimetres below the canker. Where cankers occur on the main trunk, it is sometimes possible to save the tree by cutting away diseased tissue and encouraging the bark to heal around the wound. Surgically removing cankers on main trunks of infected trees is time consuming and often not completely successful. 
  • Inspect alternative hosts such as crab apple, pear, quince, peach, serviceberry, apricot, cherry, flower quince, hawthorn, and mountain ash for cankers and remove cankers.
  • Burn prunings or remove them from the orchard promptly. If this is not possible, chopping prunings hastens their breakdown and reduces the risk of disease spread.
  • Inspect nursery stock carefully before planting and discard any trees with cankers.