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Causes of Cankers on Limbs and Trunks

On this page
  • Black streak
  • Bacterial canker
  • Dothiorella canker
  • Phytophthora canker and collar rot
  • Sunblotch
  • Mechanical injury
  • Wildland fire
  • Sunburn
  • Vertebrates

Names link to more information on identification and management.

Click on photos to enlarge
Cankers on limbs and trunks caused by pathogens

Black streak
Black streak
Identification tip: Dark staining and powdery white exudate, typically occurring on trees stressed by insufficient irrigation and excess salts in water.

Black streak
Black streak
Identification tip: Infected cambium exposed by cutting under discolored bark.
Bacterial canker
Bacterial canker
Identification tip: Liquid or pale, dry ooze, often occurring in small patches in a row on bark.
Dothiorella canker
Dothiorella canker
Identification tip: Exudate and dark discoloring on infected green bark of young trunk.

Dothiorella canker
Dothiorella canker
Identification tip: Cankered graft union from young tree killed in the field by fungal infection caused by contaminated nursery stock.

Dothiorella canker
Dothiorella canker
Identification tip: Exudate and dark discoloring on older trees typically occurs on bark at least several feet aboveground.

Phytophthora canker and collar rot
Phytophthora canker and collar rot
Identification tip: Symptoms usually appear relatively low on the trunk.

Phytophthora canker and collar rot
Phytophthora canker and collar rot
Identification tip: Cracked, flaking bark from fungal infection near the root crown.

Sunblotch
Sunblotch
Identification tip: Rectangular cracking or checking on limb or trunk, called alligator bark.

Cankers on limbs and trunks, caused by abiotic disorders—Top of page

Mechanical injury to tree
Mechanical injury
Identification tip: Old wound from chemical injection into trunk.

Mechanical injury to tree
Mechanical injury
Identification tip: Hatchet cuts made before spraying chemical onto trunk bark.
Mechanical injury
Mechanical injury
Identification tip: Old wound closing as cambial tissue grows.
Mechanical injury
Mechanical injury from too tightly staking and tying a trunk.
Cracked, discolored bark
Cracked, discolored bark on trunk killed by wildland fire.
Sunburn, cracked and roughened bark
Sunburn
Identification tip: Cracked and roughened bark from heat damage to formerly shaded limb exposed to direct light after extensive pruning.
Cankers on limbs and trunks, caused by vertebrates—Top of page
Bark gnawed by rabbits
Rabbits
Identification tip: Bark gnawed by rabbits, similar to chewing by ground squirrels and voles.
Girdled bark
Ground squirrels
Identification tip: Girdled bark and soil burrowing from ground squirrels.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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