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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Deciduous Trees > Black Walnut > Sunken, cracked or discolored areas along branches or trunk

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Black Walnut > Trunk/Branches > Sunken, cracked or discolored areas along branches or trunk

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  • Image: Perennial nectria canker 1
  • Image: Perennial nectria canker 2
  • Image: Perennial nectria canker 3

Perennial nectria canker
Neonectria ditissima

  • Early canker symptoms are small and difficult to see, usually forming a darkened, depressed area beneath smooth, young bark
  • Sunken round to oval cankers with target shaped ridges of barkless wood on large branches or main trunk
  • Red to reddish orange raised cushion like bumps can occasionally be seen on the edge of the canker
  • Dead branches and twigs killed by girdling cankers
  • More information on Perennial nectria canker
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  • Image: Fusarium canker 1

Fusarium canker
Fusarium solani

  • Cankers are elongated strips of cracked sunken bark on lower trunk of young trees
  • Wood is stained dark brown to black under bark in cankers
  • Occasionally cankers will form higher on the trunk or on branches
  • Wilting, canopy dieback and basal sprouting may accompany cankers
  • Common on trees with cracks from cold damage
  • More information on Fusarium cankers
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  • Image: Frost canker 1
  • Image: Frost canker 2

Frost Cracks

  • Vertical splits or sunken dead areas of trunk or branches that are primarily on the south and southwest side
  • Occurs during winter, often noticed early spring
  • More information on Frost Cracks
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  • Image: Thousand canker disease 1
  • Image: Thousand canker disease 2
  • Image: Thousand canker disease 3

Thousand canker disease
Geosmithia morbida

  • Leaves on one to several branches in the canopy turn yellow, wilt and turn brown
  • Dead branches appear in the top of the tree, the tree eventually dies from the top down
  • Groups of young green shoots often form on the lower trunk or branches of infected trees
  • When the bark is peeled back, numerous gray to black oval cankers can be seen, often with borer galleries
  • Bark surface may show no symptoms or may exhibit an amber stain or cracking immediately above cankers
  • 1/32nd inch or smaller exit holes from the walnut twig beetle may be visible on dead and dying branches
  • Currently not found in MN. If suspected, report it to the Minnesota Department of Agriculture at the "Arrest the Pest" Hotline: 651-201-6684 (metro) or 1-800-545-6684 (Greater Minnesota)
  • More information on Thousand Cankers Disease

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