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Thousand Cankers Disease Checklist

Is your tree a black walnut? (See Photos)

  • The Eastern black walnut is a species of flowering tree in the hickory family that is native to eastern North America.
  • Under forest competition it develops a tall, clear bole and the open-growth form has a short bole and a broad crown.
  • The bark is gray-black and deeply furrowed.

Early symptoms (late June to late August) may appear anywhere in the tree crown (upper, middle or lower)

  • A portion of the crown may look thin
  • Look for yellowing and/or wilting leaves ("flagging") in the crown
  • Attached, wilted and brown leaves may be observed in the older portion of the affected crown
  • Leaves may appear smaller than normal

Actively declining crown symptoms

  • Over several weeks, there is a rapid wilting and "collapse" (of foliage) on affected limbs
  • Cankers may be observed on branch below wilting foliage
  • Dead limbs are relatively recent, usually died within the same season but not more than one year
  • Tree affected the previous growing season has little live crown the next growing season

Late symptoms

  • Affected black walnut trees die in less than 3 years after the very first flagging symptoms are observed
  • Branches > 1 1/2 inches have numerous tiny holes (smaller than pin hole borer type holes)
  • When outer bark is carefully scraped to reveal inner bark tissue, small cankers are observed on branches. Once coalescing of cankers occurs, large, dead (cankered) areas can be found on branches and main stem
  • Numerous, meandering tunnels and galleries of the walnut twig beetle may be observed in the bark
  • Both the fungal cankers and the walnut twig beetle are found in the bark down to the cambial region (not into the wood)

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