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Plant Diseases - brown spots on maple leaves
Expert: Jim Hyland - 11/4/2009
Question
I live near Philadelphia and have an almost 30-year-old maple tree in my backyard. This fall I have noticed a predominance of brown spots on the maple leaves, and it appears that the fall colors have been less brilliant than in previous years. I am eager to know whether this is disease condition of concern, and, if so, what I can do about it. I am attaching a close-up photo of one of the leaves.
Answer
These are leaf spot caused by a fungus. I am going to guess it is Phyllostict leaf spot. A leaf spot that infects late in the growing season causes very little damage except maybe the leaves will fall earlier than normal. If you want to control the fungus the leaf surface would need to be sprayed with a fungicide in the spring. A large tree would be difficult to spray and in my opinion not worth the effort since the damage to the health of the tree is slight.
Phyllosticta Leaf Spot of Maple. Pathogen: Phyllosticta minima
Like many fungal leaf spots, this disease affects a number of maple species, most prominently Amur, Japanese, red and silver maple. The disease causes little damage because the infection is localized. Spots are roughly circular and develop into tannish spots with purple to red borders. Later in the season the spots often contain black fruiting bodies of the fungus arranged in rings inside the lesion. Although this disease is quite noticeable in the landscape, especially on silver and red maples, and causes concern among homeowners, damage is minimal and fungicides are rarely necessary. If fungicides are required use a labeled product containing mancozeb or chlorothalonil.
Most fungicides are sprayed early in the spring to prevent leaf spots. You could try a fungicide it should keep the spots from spreading but will not make the ones that are there go away. Check with your local nursery for a fungicide for leaf spots on trees.
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