Spots on maple leaves


Maple Tree Tar Spot – Managing Tar Spot Of Maples

Your maple trees are absolutely gorgeous yellow, orange and red fireballs every fall – and you look forward to it with a great deal of anticipation. When you discover that your tree is suffering from tar spot of maples, you may start to fear that it spells the end to beautiful fall scenery forever. Never fear, maple tree tar spot is a very minor disease of maple trees and you’ll have plenty of fiery falls to come.

What is Maple Tar Spot Disease?

Maple tar spot is a very visible problem for maple trees. It starts with small yellow spots on growing leaves, and by late summer these yellow spots expand into large black blotches that look like tar has been dropped on the leaves. This is because a fungal pathogen in the genus Rhytisma has taken hold.

When the fungus initially infects a leaf, it causes a small 1/8-inch (1/3 cm.) wide yellow spot. As the season progresses, that spot spreads, eventually growing up to 3/4 (2 cm.) inches wide. The spreading yellow spot also changes colors as it grows, slowly turning from a yellow-green to a deep, tarry black.

The tar spots don’t emerge right away, but are typically obvious by mid to late summer. By the end of September, those black spots are at full size and may even appear to be rippled or deeply grooved like fingerprints. Don’t worry, though; the fungus only attacks the leaves, leaving the rest of your maple tree alone.

The black spots are fairly unsightly, but they don’t do any harm to your trees and will be shed when the leaves fall. Unfortunately, maple tree tar spot is spread on the wind, which means that your tree can get reinfected next year if spores happen to hitch a ride on the right breeze.

Maple Tar Spot Treatment

Because of the way maple tar spot disease is transmitted, complete control of maple tar spot is virtually impossible on mature trees. Prevention is the key with this disease, but if nearby trees are infected, you can’t reasonably expect to totally destroy this fungus without community support.

Start by raking all your maple’s fallen leaves and burning, bagging or composting them to eliminate the closest source of tar spot spores. If you leave the fallen leaves on the ground until spring, the spores on them will likely reinfect the new foliage and start the cycle again. Trees that have trouble with tar spots year after year may also be struggling with excessive moisture. You’ll do them a great favor if you increase the grade around them to eliminate standing water and prevent moisture build-up.

Young trees may require treatment, especially if other trees have had a lot of their leaf surfaces covered by tar spots in the recent past. If you’re planting a younger maple in an area prone to maple tar spot, though, applying a fungicide, like triadimefon and mancozeb, at bud break and twice again in 7- to 14-day intervals is recommended. Once your tree is well-established and too tall to easily spray, it should be able to fend for itself.

black spots on maple tree leaves

These spots are from a fungal disease called anthracnose that is caused by the long periods of wet conditions in May. It is not something that can be treated for at this point and as we get into warmer and drier conditions in summer the spread of the fungus will stop. It is generally not a disease that is sprayed for since it takes just the right environmental conditions for the disease to spread. We see this yearly on many silver maples and those that are crossed with red maples but it is usually so minimal that it goes unnoticed. Usually the tree still has the majority of leaves and they continue to function and it has little impact on the tree. Maples continue for awhile to push out more leaves in early summer and these will likely not be impacted since the conditions are different from spring. One of our pathologists wrote an article on this topic in 2009 when conditions were very similar. Please click on the following link to read her article:

What Are These Black Spots On The Leaves?

Walking to my garage this morning I happened to notice these yucky black spots on the fallen leaves from my maple tree.

What are they?

Is it the tree diseased?

Will it spread to the other trees around it?

It looks really gross.

According to Chicago Botanic, these spots are a fungus called “maple leaf tar spot, known scientifically as species of Rhytisma fungi.”

Will it hurt my tree?

Gardening Know How says that “the fungus only attacks the leaves, leaving the rest of your maple tree alone.”

Whew! That’s a relief.

What can be done about it?

Because the fungus is spread by the wind blowing the spores around, totally eliminating it is impossible. Well that stinks.

However, the article says to prevent it from spreading I can start by raking up the leaves and either burning them or bagging them up for compost.

Also, it stated that your trees suffer from this every year, they are quite possibly in an area of heavy moisture.

A way to combat it is to grade the area to get rid of extra moisture and standing water.

Hmm… we have had a lot of rain this past spring and basically all summer so I’m wondering if this is the culprit?

I’m glad to know it isn’t going to kill my beautiful maple tree. I love its shade in the spring and summer and of course its colors in the fall. I would hate to loose it from my yard.

If you see this on your trees leaves, now you know what it is and what to do about it.

As they say “the more you know, the more you grow.” Knowledge is Power.

Ok. Enough of my after school PSA, continue on with your day.

why would maple tree leaves curl in one day and be brown the next

The leaves curled and turned brown from not enough water in the root area. Even though you have two maples, they are not twins or clones. One may have a smaller root system or some defect below ground that is exacerbating the problem.

Not knowing how much rain your area received, it is possible that a few deep watering events were not enough. A lawn irrigation system is useless when conditions are dry… under one inch of water per week falling out of the sky. If the lawn irrigation system is set up correctly, it only puts down enough water in a week to dampen the top 2-3 inches of soil. Most of your tree roots are in the top 18-24 inches of soil. So it is possible that there was not enough water or not often enough or deep enough.

The leaves on the tree were probably a lighter green before they curled and turned brown. By the time they were curling, they were dead and dry. Brown is just the end and brown leaves never come back to life. If the leaves were a lighter green, they could have been dead then.

If you think it was the lawn company, then all your trees would be doing exactly the same. Most companies divide applications into small amounts because they are charging you by the visit, not the gallons or pounds applied.

With new trees, you need to water them for several years. They do not develop a big enough root system in one year to handle life in general. Some trees adapt more rapidly than others. Purchase a rain gauge. Any time we have under one inch of water a week (that’s to one inch of soil below) you need to make that up. If you can dig in the soil and cannot find any damp soil in the top 4-6 inches of soil, the tree is dry.

Trees should be mulched and not have grass around them… but no mulch piled on trunks. There needs to be three inches deep of mulch that comes out farther than the ball when it was put in. You are trying to keep the soil cool and damp to enable root growth to go beyond the ball.

Do not fertilize the tree. You could finish it off. Check on moisture and mulch both trees. Right now, trees are making buds for next spring but if there is insufficient water, the tree is not going to fare well. This may just be the weaker of the two maples.

Brown edges or margins on leaves are fried. This means there was not enough moisture getting into the tree. Whether it was lack of available water or a compromised root system or a combination, it does not matter. Maples have many roots very close to the soil surface and if there is a lack of water, they are going to know about it immediately.

This is based on whether the trees were planted correctly… not above or below grade. You should be able to find big roots in the top one or possibly two inches of soil at the trunk. no deeper. If not, planting may be a problem. If there is burlap seen on the soil surface from the ball, that’s a big problem, too.

Maple Leaf Blister: Black Leaves on Maple Explained

A foliar disease called leaf blister has been common on silver and red maples and their hybrids during the past few weeks. The causal agent is the fungus Taphrina carveri. The disease may go unnoticed until a large number of leaves are severely infected and begin to fall from the tree. Symptoms include grayish brown-to-black irregularly-shaped, slightly-raised but not always obvious blisters on the leaves. The leaf blisters turn black, often lighter-colored in the center. (Fig. 1) Multiple infections will cause the leaf to become distorted. (Fig. 2) The rounded shape of the spots and blistering distinguish this disease from maple anthracnose, which produces irregularly shaped brown spots or blotches that follow the veins of leaves and is caused by a different fungus. Leaf blister and anthracnose can occur on the same tree and even on the same leaf.

Taprhina spp. overwinters on bud scales. Infection occurs on developing leaves early in the spring when buds open if environmental conditions are favorable for the disease. Optimal conditions for this pathogen are over 12.5 hours of leaf wetness and temperatures below 61 degrees F. Severe infection, along with defoliation, may occur if these weather patterns persist. Less severely affected leaves may remain on the tree all season. If defoliation does occur, the lost leaves will almost always be replaced by new ones within several weeks to a month. The high-risk period for infection is when leaves are very young; later in the season, leaves become resistant to the fungi, so there are no repeat cycles of infection in the same season.

Leaf blister is an occasional problem in Iowa and elsewhere in the Upper Midwest (see University of Minnesota Yard and Garden Line News, July 1, 2002

Why are maple trees losing their leaves?

Anthracnose is the more serious of the diseases affecting the plants.

“If Anthracnose gets started in June or July and causes significant defoliation, then if it is a wetter growing season again the following year, a homeowner may want to treat the tree to protect the foliage,” said Sandra Jensen, a diagnostician with the Plant Disease Diagnostic Clinic at Cornell University. “Trees are resilient, so one year of early leaf loss may be tolerated, but you don’t want two or more consecutive years of early defoliation. If the disease occurs late enough in the growing season however, mid-August or later, the tree has already stored adequate energy so it’s less of an issue.”

Mathers said he noticed Anthracnose trees on silver maples earlier in the season.

In regards to tar spots, it is unlikely there are severe infestations in two consecutive years because the leaves fall early and should be buried underneath uninfected leaves.

In addition to maple trees, Mathers said other trees and plants are facing negative conditions.

“Hawthorn and crabapple trees have lost a lot of leaves,” Mathers said. “I was driving and I could see through the canopy of a tree that before I couldn’t normally see through.”

Follow @MSteecker on Twitter.

What are these ugly bumps on my tree’s leaves?

Galls galore

Plants often develop bumps or other odd growths that might remind one of a science fiction movie, but there’s no need to be alarmed. These unusual, and often ugly, growths are called galls and are usually more of a cosmetic problem rather than a health crisis.

Galls usually form in response to the presence of some insects or mites and may appear as balls, knobs, lumps or warts, each being characteristic of the specific causal organism. In addition to their unusual structure, galls may draw attention due to their range of colors: red, green, yellow or black.

While leaf galls are the most commonly seen plant galls, galls can occur on twigs, buds and roots. Galls can be induced by viruses, bacteria, nematodes and fungi as well as insects and mites. Factors such as weather, plant susceptibility and pest populations affect the occurrence of galls on plants from year to year.

Common galls

Michigan State University Extension experts commonly receive questions about the following galls on trees.

Maple bladder galls result from abnormal leaf growth due to stimulation or “irritation” from the feeding of mites. Tiny growths, approximately 0.125 inches in size, occur primarily on the upper surfaces of maple leaves. Newly formed galls are yellowish-green, but later become pinkish to red and finally black.

Maple bladder gall on silver maple.
Photo credit: MN Dept. of Natural Resources Archive, MN Dept. of Natural Resources,

Maple spindle galls are also caused by mites. The galls are about 0.2 inches long, as thick as pencil lead and stand erect.

Maple spindle gall.
Photo credit: E. Bradford Walker, VT Dept. of Forests, Parks and Recreation,

Oak apple galls are 1- to 2-inch diameter round growths on oak leaves and are caused by wasps. The “apples” are filled with a spongy mass that contains a single, hard, seed-like cell. As the galls mature they become papery.

Oak apple gall. Photo credit: Steven Katovich, USDA Forest Service,

Gouty oak galls and horned oak galls are two twig and stem galls caused by wasp infestations. The resulting solid, woody gall masses can grow over 2 inches in diameter and girdle branches. Heavy infestations are uncommon, but high numbers can be especially devastating to young trees.

Horned oak galls develop on the twigs of black and pin oaks. Small horns protrude through the gall surface and a small, stingless wasp develops in each horn. Photo credit: John A. Weidhass, Virginia Polytechnic Institute and State Univ.,

Gouty oak galls are smooth and occur on scarlet, red, pin and
black oak. Photo credit: Rebekah D. Wallace, Univ. of Georgia,

Cooley spruce galls are a 1- to 1.5-inch, cone-shaped overgrowth that appears on the tips of the spruce branches in early June. If cut open, one will find numerous tiny gray aphids (adelgids) inside. The galls open in August and September, and the adults emerge to lay eggs. The young adelgids overwinter on the buds and twigs of the host tree.

Cooley spruce galls on Colorado blue spruce in late summer. Note
openings where insects have emerged. Photo credit: Mary Wilson, MSU Extension

Homeowner actions

While the presence of plant galls on your favorite tree may be unsettling, chemical control is seldom suggested for their management. Consider the following tips:

Live with a minor infestation. Although unattractive, galls will probably not kill your tree and usually natural controls will reduce the population in succeeding years.

Use cultural methods to reduce the impacts of these infestations. Some fallen leaves may harbor various life stages of gall-producing pests. Rake and destroy all gall-infested leaves. Prune and destroy twigs infested with gouty oak gall and horned oak gall on small and lightly-infested trees to help reduce potential girdling. This action should be done when the galls are small and have just started to develop on the twigs.

Maintain tree health by watering during dry periods and fertilizing if needed.

Be a smart and environmentally-conscience gardener. Remember that infestations are unlikely to be controlled by chemical treatment. By the time galls become noticeable, the causal pest is confined within the gall and physically protected from chemical sprays. Attempts to control many plant galls may result in more harm to the plant or the environment than good, while achieving little actual success in eliminating the gall problem on the plant.

More information on galls of trees and shrubs can be found in the following publications:

For more information on a wide variety of smart gardening articles, classes and events, visit

Watering Young Maple Trees

A dying maple that has put on only a few leaves this year.

Young trees require additional attention during their first two years after planting as they struggle to survive in their new environment. Trees can lose 60 to 75 per cent of their roots during the digging process at the nursery. Newly planted trees require regular watering during periods when there is little rainfall. Some Arborists recommend watering young trees twice a week. Without new root development, they are less able to absorb water and nutrients. The first summer is the most challenging for newly planted trees. Watch for signs of drought stress which include wilting of leaves and new growth, scorching of the leaf edges and dry, curled leaves.


Besides keeping weeds down, covering the soil around the tree with an 8 to 10 cm deep layer of mulch material cools the root zone and reduces evaporation and creates a healthier environment for the soil organisms that are beneficial to the tree.

Check Caring for your Maple and consider the use of Wood Chips as described in this article: Mulches Help Trees Beat Weed Competition.

How Often and How Much Should I Water my young Maple Tree?

The timing, frequency and volume of water that is needed is dependent on the species and size of tree, the soil type (sand, loam, clay, silt), how well it drains, how long the tree has been planted and if the tree was mulched after planting.

There is no easy answer to, “How often and how much”? but there are some general guidelines.


Use a garden trowel or spade to dig into the soil (near the tree) to a depth of 10-15 cm. If the soil is cool/moist to your touch, watering is not needed at this time. Check the tree again in another 4-5 days to determine when to resume regular watering.


Watering early in the morning or late evening reduces evaporation and helps the water soak into the soil. Use a watering can or a slow steady stream from a lawn hose to completely soak the mulch (or soil) around the base of the tree to a depth of 20-25 cm. This takes time and lots of water.

An alternate method is to use a 20 liter bucket and drill 1/8 inch holes in the bottom. Place the bucket close to the base of the tree and fill 4 times (normal) or 8 times (drought) per week.


A general rule of thumb is to apply 45 liters (10 gallons) of water for every 2.5 cm (inch) of trunk diameter during normal watering conditions. The amount applied per watering remains the same but the frequency is doubled to twice a week during drought conditions. This gets the water deeper into the soil where the tree’s roots are and encourages the formation of deeper roots on the tree. This is beneficial to the tree as the availability of moisture increases with soil depth. Watering should moisten the soil to a depth of 20-25 cm. around the tree.

Sandy and loamy soils absorb water more quickly than heavier soil types and drain faster requiring more watering, more frequently. Compacted soils or soils with higher clay/silt content require longer times to become wet and stay wet longer. Care should be taken not to allow heavier soils to become in a constant “wet state” due to frequency and amount of water applied. Good soil aeration is required for healthy root growth and tree survival.

To help new trees get established, landowners have to make up for what Mother Nature is not providing. Helping young Maples through difficult times will encourage more growth when growing conditions improve.

  • Watering Your New Tree (PDF) – Kitchener’s Urban Forests –
  • How to Water Trees With Buckets – Amelia Allonsly, DM –
  • How much water does my tree need? – Deborah Benge-Frost –
Written by Carl Mansfield, Arboreal Consultant, Maple Leaves Forever
Setup and Editing by Mary Bella, Webmaster & Communications, Maple Leaves Forever

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

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.


Gabor Degre | BDN Gabor Degre | BDN Leaves of a norway maple in Bangor exhibit signs of “tar spots,” a fungus that has been aggravated by the wet weather early this summer. The infections, which are not fatal to the trees, cause the leaves to fall to the ground in the summer. By Lauren Abbate, BDN Staff • September 16, 2017 7:00 am
Updated: September 18, 2017 10:06 am

If you look closely at the trees, the Norway maples in particular, around where you live, you’ll likely notice the leaves aren’t looking so good. Covered in black blotches, the leaves’ sad conditions are a direct correlation to the overly damp start to summer.

The culprit? The black tar spot fungus.

“It’s unusually bad this year because of the wet and cool weather we had during the months of May and June,” Aaron Bergdahl, a Maine Forest Service pathologist, said. “Trees are just ghosts of themselves.”

The black tar spot fungus affects Norway maple trees, which are native species of Europe, not New England, according to William Livingston, a professor of forest resources at the University of Maine. However, the trees are prevalent throughout much of the northeast. This specific fungus does not impact the region’s native maple trees.

In August and until the trees start to defoliate in late September or October the fungus can be identified in the form of black spots on the leaves of the trees. The spots vary in size but can be as large as a nickel and are ringed by a yellowish halo.

While the fungus becomes more visible towards the middle and end of summer, the stealth disease claims the Norway maple leaves as its victims as the leaves are budding in the spring. At this time, any infected leaves that remain on the ground from the previous fall can release fungal spores that have remained dormant, Livingston said. Since fungi thrive in moist conditions, a wet spring can amplify the spreading of these spores, as it did this year.

Some tar spots are noticed on the leaves in lower canopy of trees, where conditions typically are the most moist, but Bergdahl said the conditions this year are much worse, especially in Greater Bangor and central Maine.

“This year it’s so bad, and we had such prolonged periods of moisture that entire trees are infected from top to bottom,” Bergdahl said.

Even though the trees look blighted with the blackened leaves, the tar spot fungus is generally not detrimental to the health of the overall tree, Bergdahl said. No one should run out and starting cutting down their trees. The harm is being done to the leaf itself.

“ just feeding on the leaf for its food,” Livingston said. “So it’s like mold growing on bread that’s getting food from the bread.”

If there are bad outbreaks of the fungus several seasons in a row, Bergdahl said, the health of the tree could be impacted. He said that situation is not likely.

Since the fungus is using the leaf for food, in some instances black tar spot fungus can lead to the early defoliation of trees, which Bergdahl said is happening. However, if this defoliation begins in September it is not a huge issue, given that by this time of year the trees have already generated about as much food as they are going to for the season, Livingston said.

In addition to the tar spot causing some premature defoliation, the dry conditions that have persisted through much of mid- and late summer also are “exacerbating” this year’s early defoliation, Bergdahl said.

Because the fungus is causing Norway maples to drop their leaves early, those trees might not be dazzling any leaf peepers this fall. But the early defoliation of leaves that carry the tar spot fungus could be beneficial to preventing further outbreaks in a forest setting, according to Bergdahl. With the tar spot leaves falling first, they will be covered on the forest floor by other leaves not carrying the fungus, which will lessen the risk that they could release their fungal spores if conditions are ripe next spring.

The best thing people can do right now with the blighted leaves is to rake them once they have fallen and either bag them and dispose of them or burn them in a safe environment, Bergdahl said.

“Hold out, and wait to see how come out next spring,” Bergdahl said. “Chances are they’re going to be fine, they’re going to be beautiful and they’re going to be much healthier than they are this year.”

Correction: An earlier version of this story misspelled Aaron Bergdahl’s name.

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