Plant Problem Diagnosis Key / Diseases
Disease
Tar spot of maple
Rhytisma spp.
A fungus that makes raised black spots on maple leaves in late summer. It is cosmetic: the leaves have done their work by then, and it does not hurt the tree.
Signs
- Raised, shiny black spots like drops of tar, up to about 3/4 inch across.
- Pale yellow-green spots earlier in summer that turn black.
- Mostly on maples; also willow, holly and tulip-tree. Heaviest in wet years.
What favors it
Wet springs; spores come from last year's spotted leaves on the ground.
Prevention
- Rake and remove maple leaves in fall.
Crops it shows up on
Shade & ornamental trees.
Often confused with
Sources
- Tar Spot of MapleUMass Amherst Extension
- Tar Spot of Trees and ShrubsUniversity of Wisconsin-Madison Extension
Treatment by crop
Cultural, biological and chemical options in the order to use them, and notes written for each crop.
Identification is free. Treatment is on the Home and Pro plans.
Questions in the key that lead here
- Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
No, only damage or discoloration - Where is the problem?
A tree or shrub - Which part of the tree or shrub shows the problem?
Leaves of a broadleaf tree or shrub - What do the leaves show?
Spots, blotches, bumps or a coating - What do the spots look like?
Raised, shiny black spots like drops of tar
Not a match? Start the key or describe what you see.
More photos
More from university Extension: search Extension pages on tar spot of maple, or find a plant diagnostic lab through your state's Extension.
Other diseases
- Anthracnose
- Apple scab
- Bacterial leaf scorch
- Bacterial leaf spot
- Bacterial wetwood (slime flux)
- Bacterial wilt of cucurbits
- Black knot
- Black spot of rose
- Bleeding canker
- Boxwood blight
- Canker diseases
- Cedar-apple and related rusts
- Crown gall
- Damping-off
- Downy mildew
- Dutch elm disease
- Early blight and Alternaria leaf spot
- Elm yellows (phloem necrosis)
- Fire blight
- Fusarium wilt
- Gray mold (Botrytis)
- Late blight
- Mosaic viruses
- Needle cast and tip blight
- Oak wilt
- Powdery mildew
- Root and butt rot
- Root rot (Pythium and Phytophthora)
- Rust
- Septoria leaf spot
- Shade tree anthracnose
- Sooty mold
- Tomato spotted wilt and impatiens necrotic spot viruses
- Verticillium wilt
- White mold (Sclerotinia)
- White pine blister rust