Tree Notes is about trees -- especially native trees, trees for wildlife, and trees in history.

Monday, July 28, 2008

Tar Spot on Maples

Maple fungus


I've been studying about tar spot, a fungus on maples, this evening, after reading an article in the Detroit Free Press. It seems that tar spot is a bigger problem recently in Michigan and throughout the Midwest. The article includes a really ugly photo of maple leaves with big black blotches on them. Tar spot was also a problem in heavily-mapled Massachusetts a couple of years ago.

Tar spot is caused by Rhytisma fungi. (There are a couple of types.) The fungus actually starts growing on the leaf early in the growing season, but it's a pale yellow then and not too noticable. In late summer, the fungus darkens to the tar-like color for which it is named and becomes a raised-up spot on the leaf.

The affected leaves usually fall from the trees early. After overwintering on the leaf, the fungus finally releases its spores in the spring -- just at the right time for the wind to carry the spores to an emerging tree leaf.

To interrupt the cycle, rake and remove the infected leaves as they fall in the late summer. Cornell University's fact sheet on tar spot says that composting the leaves will kill most of the fungus, but to be safe, cover or turn over the compost before the trees begin getting their leaves in spring.

We have quite a few maples on our little rural property, so I hope the fungus doesn't get started here. However, it's more of a disfiguration and inconvenience than a lethal threat. Healthy unstressed trees can withstand an infection of tar spot.

Related:
Images of tar spot

2 comments -- please add yours:

Chuck said...

Genevieve, I've only seen a few of your posts but I enjoy them; they're really varied and original. Are you thinking to post much more?

Chuck
www.arborday.org/blog

Genevieve said...

Thank you for the encouragement, Chuck. Recently, I've been devoting most of my writing time to my other blog, Prairie Bluestem.

However, I'm in the process of setting up an office in the bedroom my daughter no longer needs. There, I'll be able to leave things spread out until I am finished with them. It will be much easier for me to write in Tree Notes than it is now.

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"The power to recognize trees at a glance without examining their leaves or flowers or fruit as they are seen, for example, from the car-window during a railroad journey, can only be acquired by studying them as they grow under all possible conditions over wide areas of territory. Such an attainment may not have much practical value, but once acquired it gives to the possessor a good deal of pleasure which is denied to less fortunate travelers."

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Print references I frequently consult

Benvie, Sam. Encyclopedia of North American Trees. Buffalo, NY: Firefly, 2000.

Brockman, C. Frank. Trees of North America: A Guide to Field Identification. Ed. Herbert S. Zim. New York: Golden, 1986.

Cliburn, Jerry, and Ginny Clomps. A Key to Missouri Trees in Winter: An Identification Guide. Conservation Commission of the State of Missouri, 1980.

Collingwood, G. H., Warren David Brush, and Devereux Butcher. Knowing Your Trees. Washington: American Forestry Association, 1978.

Dirr, Michael. Dirr's Hardy Trees and Shrubs: an Illustrated Encyclopedia. Portland, Or.: Timber, 1997.

Elias, Thomas S. The Complete Trees of North America; Field Guide and Natural History. New York: Book Division, Times Mirror Magazines, 1980.

Grimm, William Carey. The Book of Trees;. Harrisburg, PA: Stackpole, 1962.

Hightshoe, Gary L. Native Trees, Shrubs, and Vines for Urban and Rural America: a Planting Design Manual for Environmental Designers. New York: Van Nostrand Reinhold, 1988.

Little, Elbert L. National Audubon Society Field Guide to North American Trees. New York: Chanticleer, 1996.

Martin, Alexander C., Herbert S. Zim, and Arnold L. Nelson. American Wildlife and Plants. New York: McGraw Hill, 1951.

Mitchell, Alan F., and David More. The Trees of North America. New York, NY: Facts On File Publications, 1987.

Randall, Charles E. Enjoying Our Trees. Washington: American Forestry Association, 1969.

Settergren, Carl D., and R. E. McDermott. Trees of Missouri. Columbia: University Extension, 1995.

Sternberg, Guy, and James W. Wilson. Native Trees for North American Landscapes: from the Atlantic to the Rockies. Portland: Timber, 2004.

Wharton, Mary E., and Roger W. Barbour. Trees and Shrubs of Kentucky. Lexington: University of Kentucky, 1973.

Wyman, Donald. Trees for American Gardens. New York: Macmillan, 1965.

Photos and text copyright © 2006-2010 by Genevieve L. Netz. All rights reserved. Do not republish without written permission. My e-mail address is gnetz51@gmail.com