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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Deciduous Trees > Black Walnut > Tiny to small holes in trunk or branches

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Black Walnut > Trunk/Branches > Tiny to small holes in trunk or branches

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Yellow bellied sapsucker
Sphyrapicus varius

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Flat headed apple tree borer
Chrysobothris femorata

  • ¼ inch oval-shaped exit holes present
  • Older tunnels cause cracks in bark, froth oozes from openings
  • Infected areas of tree show sunken, darkened areas of bark
  • Larvae tunnel under bark of large branches and trunk
  • Can cause dieback or entire tree can be killed, especially young trees
  • Larvae is yellow with no legs
  • Adult is ¼ to ½ inch long, flattened beetle, ranging from metallic brown to dull gray
  • More information on Flat-headed apple tree borer...
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Thousand canker disease
Geosmithia morbida

  • 1/32nd inch or smaller exit holes from the walnut twig beetle may be visible on dead and dying branches
  • 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
  • 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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