Managing Tar Spot on Maples - Maple Tree Tar Spot Disease

July, 2004
David L. Roberts, Ph.D.
Michigan State University Extension

Managing Tar Spot on Maple
Tar spot on maple, caused by the fungus Tarus Spotius Maximilius (just kidding), has been quite conspicuous on maples in many areas of Michigan for several weeks now. This disease has been prominent for at least five years, especially in some areas where the disease was not common in previous years. Presumably, high levels of pathogen spores from infection in previous years accompanied by conducive environmental conditions this past spring initiated high levels of infections. This disease begins in the spring with pinpoint infections on the foliage -- you may have noted tiny, yellow spots in the spring and early summer. (Fig. #3) These small, yellow spots have now enlarged to large, yellow spots up to an inch or so in diameter over the course of the summer and have now become dark (Fig. #4) with the production of fungal mycelium and fructifications. (Fig. #1 & #2)

David L. Roberts, Ph.D.
Michigan State University Extension Southeast
28115 Meadowbrook Rd., Novi, MI 48377-3128
Campus:
Michigan State University
B17 Plant & Soil Sciences
East Lansing, MI 48824-1359
For comments or questions email: robertsd@msu.edu

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