This fungus impacts the leaves of the tree and forms black spots on the topside.

Black fruiting pods may appear on these leaves, which then cause leaf fall.

Read on to learn what this disease is and how to protect your maple trees against it.

The solution to eliminating black spots on maple

Gather and burn all the leaves to eliminate any chance of having the fungus survive.

You can also put them in the compost.

What causes maple leaf black spot?

A fungus called Rhytisma acerinum is responsible for this. It’s commonly called “tar spot” or “black tar spot” because it’s black as pitch.

The fungus doesn’t infect the inside of the tree, and it doesn’t have any severe parasitic action. The worst impact of this fungus is that it shuts down normal activity on leaves at the spot itself – that reduces the leave’s ability to photosynthesize and convert sap and sun to nutrients and energy for the tree.

The visual effect makes the tree look much sicker than it actually is.

Why raking up leaves under the maple is important for black tar spot

This particular fungus has three main phases in its life cycle –

  • in spring, microscopic spores are released which are airborne. The wind carries them over a distance and some of them land on maple tree leaves.
  • the sticky spores open up and start colonizing the leaf, and the imbalance resulting from this causes the maple leaves to form yellow spots.
  • the fungus keeps growing when leaves fall off for as long as the weather stays moist – which, for fallen leaves, is all winter long.

Over the winter, the fungus forms capsules which contain many new spores that will burst open when temperatures rise again after winter, starting the cycle all over again.

Removing the leaves before winter ensures that most of the hibernating spores are destroyed.

Composting leaves infected with maple black spot also works because the spores will be buried and will die off or be broken down before being exposed to air again.

Smart tip about black maple spot

It isn’t necessary to treat the tree with chemicals. Let’s avoid contaminating our planet.

Read also:

  • Black spots, but not on maple? Treating black spot disease on leaves
  • Organic ways of dealing with fungus in the garden

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Black spots on maple leaf by Petra Karrasch ★ under license

Have the leaves on your gorgeous maple tree become blotted with ugly, dark brown spots? If so, you’re probably thinking that your once beautiful maple tree has become an eyesore. Never fear. The Mr. Tree arborists are here. We’ll tell you exactly what’s causing those troublesome spots and just how to fix them!

Let’s first get to the root of the matter and talk about the cause of those blemishes. Brown spots appearing on maple tree leaves or on the leaves of box elder trees are typically caused by something known as tar spot. This fungal disease gets its name from the fact that the dark brown spots resemble tar. The good news is that while this disease causes blotchy brown spots to pop up on the tree’s leaves, it doesn’t impact the tree’s overall health. The bad news is that in addition to the fact that the spots aren’t exactly aesthetically pleasing, tar spot often causes the tree’s leaves to prematurely fall.

So what should a homeowner look out for when it comes to tar spot? You’ll want to begin checking your maple trees in early spring. If a maple tree has become diseased, you’ll begin to notice light green or yellowish green spots. The spots will gradually become larger and darker until they begin to resemble tar, usually around late September.

Now that we’ve diagnosed the problem, how exactly do we fix it? Since tar spot causes the tree to lose its foliage, you’ll want to be diligent in raking and destroying the fallen leaves by burning, burying, or composting them. This removal process will reduce the chance that the diseased leaves will infect new spring foliage. Without properly disposing of the leaves, however, you run the risk that the fungal spores will be carried on the wind and spread back to the tree’s new foliage.

While destroying all the infected leaves should do the trick, there are certain situations that may call for additional measures. Perhaps, for instance, tar spot has been a persistent problem on your maple tree and you’re looking for a more permanent solution. If this is the case, you may want to contact your local arborist at Mr. Tree to apply fungicide to your maple tree. While it may be possible to tackle this as a do-it-yourself project on smaller trees, larger trees often require a professional fungicide application.

To rid the tree of tar spot, the fungicide must cover every leaf on your maple tree. For mature trees, this can be quite the task. The last thing you want is to take the time and effort to apply fungicide, only to have tar spot return again next year. In order to ensure that the fungicide is applied properly and that every leaf is sprayed, you should contact your local arborist to professionally treat your maple tree.

If you do decide to treat the tree with fungicide yourself, remember that you’ll have to perform multiple sprays in order for the fungicide to be effective. You should perform the first application at bud break and then twice more after a period of seven to fourteen days.

Since tar spot is often a recurring problem, it’s best to try to prevent it altogether. There are several steps you can take in order to decrease the likelihood your maple tree will become infested with tar spot. First, remember that diseases often flourish in wet conditions, so be careful not to overwater your tree. A good rule of thumb is to water the tree so that only six to eight inches of the soil is moist. The soil should be completely dry by the time of the next watering.

You should also prune your tree on a regular basis to increase the amount of sunlight it receives and improve air circulation through the tree’s canopy. Ornamental trees, such as maple trees, should be pruned every year. Finally, add a layer of mulch to your tree on an annual basis as well. The layer should be three to four inches deep and located at least two inches away from the tree.

It’s also a good idea to perform a soil test on your tree from time to time to make sure it’s adequately nourished. A soil test will determine if and what nutrients are lacking. Applying fertilizer can provide nutrients for your soil if there is a deficiency and it is also a good preventative measure for maintaining the overall health of your tree. Soil nutrients should be added to trees every one to three years. While even properly maintained and cared for trees can become diseased, taking these preventative measures will greatly reduce the risk that a tree will become infected.

In addition to properly caring for your trees, it’s also important to have them regularly serviced by a certified professional. Our expert arborists are able to assess your tree’s health and provide honest feedback and recommendations for its upkeep. Not only will regular service appointments increase your tree’s longevity, it will also save you more money over time. Improperly maintained trees will require more attention and may even need to be removed altogether.

While it may be upsetting to see unsightly, brown or black spots on your maple tree’s leaves, you can be assured that this is a problem that can be fixed with just a little time and effort. Your tree’s overall health likely won’t be compromised and with a little TLC, your tree’s leaves will return to normal by the next growing season.

If for some reason the problem persists, just give us a call. We’re more than happy to help you get rid of those pesky spots for good!

Tagged as: caring for Maple trees, Maple leaf spots, Maple leaves spots, Maple tree care, Maple tree disease

Frequently Asked Questions About Black Spots on Maple Tree Leaves

Every spring and summer, we get calls from Milwaukee area homeowners concerned about black spots on the leaves of their maple trees. The spots appear on leaves in the spring as small, light green to yellow spots with bumpy, dark discolorations inside them and progress over the spring and summer into larger and thicker black spots about half an inch to an inch in diameter. It looks like the leaves have been splashed with tar. Hence the name: Tar Spot.

Here’s what tar spot looks like:

In spring/early summer, tar spot appears as dark, raised bumps within light green to yellow splotches. By midsummer, the tar spots have become black splotches 1/2″ to 1″ in diameter and 1 to 2mm thick.

What Causes Tar Spot on Maple Tree Leaves?

Tar Spot is a fungal disease caused by fungi in the Rhytisma acerinum genus. It infects silver maple, sugar maple, red maple and Norway maple trees, and the related box elder tree. Trees in damp, sheltered spots tend to be the most prone to tar spotting.

Is Tar Spot Unique to Wisconsin?

No, tar spot is common on maple trees throughout the US.

Is Tar Spot Anything To Be Concerned About?

In most cases, tar spot doesn’t cause any damage to the tree (other than cosmetically), although heavy infections of tar spot can cause leaves to drop well before fall arrives.

Is There Any Treatment for Tar Spot?

Tar spot can be treated with fungicides, but it’s rarely successful—especially if the trees are mature. Usually, we recommend managing the infestation by raking and destroying/disposing of fallen leaves from the tree in the fall. This minimizes the chance of fungi spores that survive on the fallen leaves infecting the tree again in the spring. The problem is that if leaves from other afflicted maples in the neighborhood aren’t also destroyed, the fungus can easily spread to your tree again.

Although some sources say the leaves can be mulched and composted, this requires frequent turning of the leaves to ensure the compost pile stays hot enough to destroy the spores on the leaves. If you are not prepared to do this, you’re better off raking them for the seasonal leaf pickup.

Bottom line: Don’t worry if your maples have tar spot. Just make a concerted effort to rake up all the leaves in the fall. Some sources say the spores will die if the leaves are mulched and composted, then turned regularly. If you’re really concerned about tar spot, though, you probably don’t want to take any chances. Your best bet is to get all the fallen leaves to the curb for pickup in the fall.

There’s one other thing you can do: If your neighbor’s trees are also affected with tar spot, let them know what you’ve learned here. If you all clean up the fallen leaves every fall, there’s a chance your trees won’t be reinfected in the spring.

Have a question about your trees? Contact our Milwaukee certified arborists now for help.

Why Are There Brown or Black Spots on My Maple Leaves?

Ah, the iconic maple leaf! It’s one of the most recognizable tree leaves out there, and it usually looks fresh! The leaves shimmer green in spring before putting on a show and turning yellow, orange, and red in fall.

But what if your maple leaves develop unsightly brown or black spots in summer? Is your tree in trouble–or even a goner?

Take a deep breath! While those spots look worrisome, it’s just tar spot–a fungal disease that isn’t a big issue to your tree’s health. Learn more about maple tar spot and how to help your tree rebound below.

Maple Tar Spot: A Tree Fungus You Can Regulate

What exactly is maple tar spot?

There are a couple types of fungi that cause those big brown or black spots on maple trees. They’re all called tar spot, and they most often affect:

  • Box elder
  • Norway maple
  • Oregon maple
  • Red maple
  • Silver maple
  • Sugar maple
  • Sycamore

As with most tree fungi, maple tar is more likely to happen if your area has been getting lots of rain!

When will I see maple tar spots?

The spots usually start developing in early-to-mid-June. Then, the dots are tiny and light green. So, you probably didn’t notice them.

Around August, those tiny spots become significantly wider and thicker. It will literally look like clumps of tar are stuck to the leaves. You may even see spots on the maple seeds – unless you were smart enough to plant a seedless maple without helicopter seeds.

Do those black spots on maple leaves hurt the tree?

Maple tar spot is mostly a cosmetic issue. The dots bring down the look of your tree – and can even cause early leaf drop.

But that’s about the extent of the issue. Maple tar spot rarely does any damage to the tree’s health.

Is there a treatment for black spots on maple tree leaves?

If you’re really fed up with the maple tar spot, you can have a certified arborist and pesticide applicator apply a fungicide next spring. This is typically only recommended if your tree continually gets maple tar or it’s a prevalent issue in your area. Most tar spot is considered aesthetic and this method usually isn’t necessary.

Plus, to be effective, the fungicide must cover every single leaf, which can be quite the feat on mature maples. That’s why it’s generally best to treat and apply a maple tar fungicide on smaller trees.

Can I prevent tar spot from happening again?

The best way to treat and prevent maple tar involves a little elbow grease! As the leaves fall, rake and destroy all leaves. Do your best to get every single leaf out of the area, which in turn will remove most of the tar spot fungal spores.

Black spot fungus on maple leaves

Without actually seeing the leaves, or not seeing a photo of them, it sounds like your maple has a fungal leaf disease called Tar Spot of Maple. If in fact this is what the problem is, the good news is your tree will recover with no ill effects. Tar spot can affect several types of maple, but Norway and silver maples are most susceptible to the disease. Infected leaves have ¼ to ¾ inch yellow blotches. A raised black spot develops in the center of the yellow blotch, which gives this disease its name. The black spot may look solid or may appear more diffuse. If you look closely in the tar-like area, you will see a pattern of lines or dots. The disease is caused by one of several species of the fungi Rhytisma. The fungi survive the winter on fallen leaves. In spring spores are produced that infect new leaves. Tar spot is a cosmetic disease. It can make the tree look bad in late summer but will not harm the tree’s health. The best way to significantly reduce or eliminate tar spot, and many other fungal leaf diseases, is a good fall clean up. Rake up all the leaves around your tree shortly after they drop and through the fall. Compost, bury or burn infected leaves to prevent spores from infecting maple leaves next year. The rake-up and clean-up method, if done meticulously, is so successful in controlling tar spot that fungicide treatments are rarely, if ever, needed. Having said that however, if you compost the leaves be sure that the temperatures get high enough to kill the spores (should be 130 degrees or higher for three days). There can be a problem with backyard composting however, in that even in the hottest of piles one can never be sure that the outside edges have heated enough. If you do decide to compost them, turn your pile or cover it in the spring as the new maple leaves begin unfurling. If you choose to use a fungicide, copper-containing fungicides are labeled for tar spot disease. Fungicides would need to be applied three times: once at bud break, once when leaves are half expanded, and once when leaves are fully unfurled. Hope this was helpful. If you do not think this is not the correct diagnosis, take some photos of the leaves and of the whole tree and send them in. We will do our best to diagnosis the problem.

If the tree has a decent amount of foliage as it may being that it is 40 years old, it can withstand this fungus. That said, taking action to control the spread would be good for aesthetics and the surrounding trees.

Maple leaves have black spots

Q. I noticed that the maples in my neighborhood have black spots on them. Are the trees sick?

A. Based on your description, it sounds like the trees are infected with maple leaf tar spot, known scientifically as species of Rhytisma fungi. Leaves that are infected with this fungal disease have round, light green to yellowish-green areas approximately ½ to 1 inch in diameter that eventually blacken. Heavily infested trees may lose their leaves prematurely. Trees infected with maple leaf tar spot are unsightly, but the fungal disease does not affect the overall health of the plants. Fungal spores can overwinter; therefore, it is important to remove all leaves as soon as they fall to lessen the impact of the disease next year. Because maple leaf tar spot is primarily a cosmetic disease, fungicide treatments are usually not necessary.

Please contact Plant Information Service at (847) 835-0972 or email [email protected] for a positive diagnosis and if you feel chemical treatment options are warranted.

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