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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Deciduous Trees > Elm > Discolored bark on branch or trunk

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Elm > Trunk/Branches > Discolored bark on branch or trunk

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  • Image: Wetwood 1
  • Image: Wetwood 2
  • Image: Wetwood 3

Wetwood or slime flux
Several species of bacteria

  • Streaks or columns of water-soaked discoloration of bark on the trunk or branches that is gray to yellow-brown when dry and black to brown when wet
  • Discoloration commonly starts at bark cracks, wounds, or branch unions
  • Fluid may ooze or bleed out of openings in the bark and may have a yeast-like odor
  • Avoid wounding the tree
  • Protect the tree from other stresses, especially soil compaction from vehicles or pedestrians
  • More information on wetwood
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  • Image: Sooty mold 1
  • Image: Sooty mold 2

Sooty mold

  • Black, brown, or gray soot-like covering on leaf surfaces, or twigs
  • Sticky, shiny secretions on leaves from sap-sucking insects (aphids, leaf hoppers, psyllids, etc.)
  • Insects or signs of insect damage (distorted, pin-prick feeding marks, etc.) may be seen on leaves above the worst affected moldy areas
  • More information on Sooty mold
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  • Image: Botryodiplodia canker 1
  • Image: Botryodiplodia canker 2

Botryodiplodia canker
Botryodiplodia ulmicola

  • Reddish brown to black water soaked cankers form on branches 4 inches in diameter or smaller
  • Sap wood underneath the canker is reddish brown
  • Leaves growing beyond the canker turn yellow and wilt (Siberian elm) or fall off (American elm)
  • Clumps of sprouts or shoots develop below cankers on large branches
  • Tiny raised pimple like fungal structures form on branches killed by the canker, causing bark to look rough
  • Damage is most severe on trees stressed by other factors
  • More information on canker

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