Larry Meiller finds out how to make the most of these final warm fall days in the garden. Plus, information about disease and pest problems this season, and a preview of a special TV program celebrating the life of Shelley Ryan, Wisconsin Gardener.
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Maple Tar Spot Looks More Serious Than It Is, Horticulturist Says
Wisconsin homeowners might be alarmed to see a maple tree’s leaves developing dark spots — but according to Lisa Johnson, it’s likely not as bad as it looks.
Johnson, a University of Wisconsin Extension horticulture educator for Dane County, said that the fungal disease known as maple tar spot has been widespread in the state this year. The disease largely has no effect on a tree’s health, she said, and is mainly a cosmetic issue, though “it does tend to catch people’s attention.”
She said it presents itself in the form of “large, raised black spots on the leaves.” Those spots are often surrounded by “a little yellow halo around the edge of the lesion.”
Norway and silver maple are the trees most susceptible to the disease, Johnson said, but other varieties are vulnerable as well. She said affected leaves generally remain on the tree as usual, but a severe case can result in some leaf drop.
Since maple tar spot affects only the appearance of the tree and not its health, Johnson said that treatment is not necessary. Instead, it’s recommended that the homeowner rake up the affected leaves and dispose of them in a way that will prevent the fungal spores from overwintering. She said that hot composting is effective, but if the compost pile is not likely to reach necessarily temperatures, bagging the leaves and disposing of them is a safer route.
The University of Wisconsin-Madison Plant Disease Diagnostic Lab has a fact sheet on Maple tar spot here.
Episode Credits
- Larry Meiller Host
- Judith Siers-Poisson Producer
- Lisa Johnson Guest
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