WSU Extension

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Caption: Maple tar spot
Photo by: R.S. Byther
  
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Maple : Tar spots
(revision date: 6/26/2015)


Biology
Tar spots are caused by a fungal infection that commonly attacks bigleaf maples and occasionally other species. In late spring to early summer, leaves develop small areas that appear water-soaked. The areas develop small, raised, glossy black tar-like spots on the upper side of the leaf between veins. The spots may develop in circular patches and are surrounded by discolored, yellowish to brown leaf tissue. Severe infections may cause some leaf drop. When leaves turn color in the fall, infected areas may remain greenish, giving a characteristic "green island" effect. Although conspicuous, tar spot infections do relatively little harm to plants.
Management Options

Non-Chemical Management
  • Rake and destroy fallen leaves.
  • Space plantings and prune to provide good air circulation.
  • Do not plant susceptible maples in moist, sheltered areas.
Select non-chemical management options as your first choice!

Chemical Management


None recommended.

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Caption: Maple tar spot
Photo by: R.S. Byther
Caption: Maple tar spot fruiting bodies close-up
Photo by: R.S. Byther