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Fungal Disease Turns Autumn Leaves Black

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CANTON - Instead of vibrant autumn colors, many of the north country's maple trees are covered with large black spots this season.
Other tree species, including ash and oak, have been hit with a fungal disease that's causing leaves to turn brown and drop off weeks earlier than usual, according to Paul H. Hetzler, horticulture and natural resource educator for Cornell Cooperative Extension of St. Lawrence County.
While unsightly, maple tree tar spot does not usually damage or kill the trees, Mr. Hetzler said.
"As long as the tree was vibrant and healthy to begin with, tar spots won't cause significant damage," Mr. Hetzler said. "Red leaf maples seem particularly susceptible to it."
During June, Mr. Hetzler said he started to receive numerous calls from north country residents concerned about black spots on their maple leaves.
The disease is caused by a fungal pathogen and is prevalent when there's been a wet spring like the north country experienced this year with record rainfalls recorded in some areas, he said.
"I've seen it throughout the region. The rainfall pattern we had was widespread from March through May," Mr. Hetzler said. "It starts when the leaves are budding in the spring."
Although all maples are susceptible, tar spot mostly affects Norway Maple, Silver Maple and Sugar Maple.
Some maple trees, as well as oak and ash trees, have been hit with anthracnose, another fungal disease.
Anthracnose looks similar to tar spot, but may causes more extensive damage. The spots are usually much smaller than tar spots, but there are more of them.
Often leaves dry out, turn brown and drop off early.
"Anthracnose has been much, much more common this year. It can impact many different types of trees," Mr. Hetzler said. "I've never seen a season like this. We've had quite a few calls."
The fungal spores can remain on leaves over the winter and are easily spread by the wind to other trees.
The disease can be controlled for next year by throwing out dead leaves, rather than mixing them in with compost.
"Raking up and disposing of leaves helps keep the spore count down," Mr. Hetzler said.

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