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Tarspot and Powdery Mildew on Maple
by Jennifer Llewellyn
October 3, 2004

There’s seems to be a record number of homeowner complaints about these diseases on maple trees this year.

Those homeowners who were blessed with Norway maples as city trees have the right to complain. Yes, they are both quite unsightly this time of year but let’s reassure those clients that no, tree health is largely unaffected. At this time of year, leaves are starting to senesce and are really not contributing much as an energy source.

Early leaf drop due to disease has very little consequence on viability this late in the season. There are no pesticides registered to manage tarspot (probably because there are none that are effective). There are a few fungicides registered to manage powdery mildew but they are most effective when symptoms are just beginning, back in late June/early July. Raking and removing fallen, diseased leaves or better yet, mulching with a mower and irrigating to accelerate breakdown are two cultural practices that will reduce disease incidence next spring.

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