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Extension > Garden > Diagnose a problem > What's wrong with my plant? > Deciduous Trees > Black Walnut > Leaves fall off prematurely

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Black Walnut > Leaves > Leaves fall off prematurely

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  • Image: Anthracnose 1
  • Image: Anthracnose 2
  • Image: Anthracnose 3

Gnomonia leptosyla

  • Leaflets have circular brown spots surrounded by yellow tissue
  • Infected leaves turn yellow, then brown on the margins, curl and eventually fall off
  • Dark brown to black spots or blotches form on nut husks
  • Nuts drop prematurely
  • More information on Walnut Anthracnose
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  • Image: Leaf spot 1
  • Image: Leaf spot 2
  • Image: Leaf spot 3

Leaf spot
Mycosphaerella juglandis

  • Small black spots scattered across leaf
  • Dark brown veins and leaf tips are common due to many spots forming on leaf veins and leaf tips
  • As the disease progresses, leaves yellow and fall off
  • In mid-summer leaves appear yellow from a distance
  • Occurs on black walnut and butternut
  • More information on Leaf spot
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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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