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Anna, Teacher, writer, biologist
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Anna, My large Maple tree has black spots on the leaves

Customer Question

Hi Anna,
My large Maple tree has black spots on the leaves again this spring? Last year was the first year this happen and I rake all the down leaves and burned them before cutting my grass. This year the black spots have spread to two other large maples in my yard? Also some of the stuff I,m reading say that the leave will fall durning the fall but on my trees the really spoted up leaves fall all summer long. Is there anything else I can do besides rake up the leaves. I dont want to loose my tress but I also dont want to rake up leaves every time I cut the grass?
Submitted: 2 years ago.
Category: General
Expert:  Anna replied 2 years ago.
Hi Mark. Thank you for requesting me. I apologize for the delay. I was not online at the time you posted your question. I just logged on and saw it.
By far the most common cause of black spots on maple leaves is something called maple tar spot. It is caused by a fungus. It actually starts out earlier in the spring with tiny yellow spots, which most of us don't notice. By summer, the spots have become black, and more noticeable. The spots can be different sizes. Maple tar spot is considered a nuisance, rather than a threat to the tree. It doesn't do permanent damage or cause the tree to die. Usually, the best course of action is to do nothing. It's not necessary to rake the leaves all summer unless you want to do it for cosmetic reasons. The fungus overwinters in fallen leaves, so you can decrease the chances of infection the following spring by raking up and destroying the fallen leaves. However, in many areas maple tar spot is so common that most of the trees are infected. You can confirm this information on Purdue University's website:
Heavy infestations of maple tar spot cause the leaves to fall. Sometimes the fungus can be controlled with applications of fungicide that completely cover the tree. The spraying has to be started at bud break and repeated several times each summer. Once the black spots have appeared, spraying will do no good during the present growing season. It also may be a waste of time when other maples are infested in the neighborhood. If you choose to spray, it is very difficult to do a thorough job, so the best course of action is to hire an arborist to do that. This site has a directory of arborists:
Anthracnose is another fungal disease that can cause spotting, but the spots are usually brown, rather than black, and the leaves often have brown, curled edges. It, too, is mostly a cosmetic problem, but if you want to treat, it would be the same as for tar spot.
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Customer: replied 2 years ago.
Ok thanks This is the second year this is happening. Will this occur every year? Last year I keep the leaves picked up.
Expert:  Anna replied 2 years ago.
Yes, it will keep happening. Even if you choose to have the trees sprayed, you'll have to repeat the spraying three times each season every year. Raking up and destroying the leave sin the fall helps mostly when only one tree is infested. In most parts of the country, a large percentage of maples are affected by this disease, and the spores are carried on the wind. That makes it impossible to eliminate the disease. In most areas, this is just a fact of life with maples.

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