When maple tree leaves turn brown, it could be because of scorch, too much watering, or not enough watering.

More specifically, there could be root damage, fungus, or problems with the soil that’s causing your maple tree’s leaves to turn brown.

There are several reasons your maple tree leaves could turn brown. A thorough inspection of the tree itself and the surrounding ground can help you understand what is causing the problem. If you can’t figure out what the problem is, you may need to consult with a Certified Arborist who can help save your trees. (A link to locate a local arborist is provided at the end of this response.)

No matter what kind of maple tree you have, when the leaves are turning brown before they should naturally, there’s a problem that needs to be addressed.

1. The Leaves Are Scorched

While this can happen nearly any time during the growing season, it typically happens during the heat of summer. Scorch happens when the moisture in the leaves is removed faster than it can be replaced. The most common cause of leaf scorch is improper watering of the tree. Though you will not be able to save the leaves that are already impacted by leaf scorch, the good news is that with proper water management your tree can recover by the next growing season.

Extreme heat can cause the leaves to dry out before the tree can pump more water into them, which will cause dried and brown outer edges, while the rest of the leaf turns yellow. As the problem continues to get worse, eventually the entire leaf can turn brown, and then it will fall off.

High winds can cause the same damage, though it’s not typically as devastating as extreme heat combined with drought. Wind scorch happens when dry air hits the leaves with damaging gusts, causing the moisture in the leaves to evaporate out.

Scorch can also happen if there is enough damage to tree roots or the tree trunk. When the tree cannot send water from the roots up to the leaves, the environment can dry out the leaves, leaving them susceptible to damage, which will cause them to turn brown.

Once leaves have been damaged by scorch, they won’t repair themselves. Dried out, brown leaves will never turn green again, so don’t worry about making them look healthy again.

What you can do is water your tree with a deep drenching. You want the water to penetrate up to two feet into the ground so the roots can get plenty of hydration. Be sure not to over-water the tree, because this can be as bad as the tree getting no water.

Watering a tree about once a month to once every three weeks is sufficient during dry months as long as the water truly goes deep into the ground. Keep in mind tree roots surpass the canopy. Sometimes they grow several times as large as the top of the tree, so water these areas as well.

https://extension.colostate.edu/topic-areas/yard-garden/leaf-scorch-2-911/
https://extension.usu.edu/planthealth/ipm/ornamental-pest-guide/abiotic/leaf-scorch
https://www.oregonlive.com/hg/2021/11/what-can-we-do-for-this-leaf-scorched-maple-ask-an-expert.html

Even though it is most likely that your maple tree has Leaf Scorch, there are other reasons your maple’s leaves are turning brown.

2. Fungus Can Cause Brown Leaves

Brown and spotted maple leaves with holes and damage.

There are a few fungal infections that can cause a tree’s leaves to turn brown and unsightly. Some of these are not life-threatening to the tree and will clean up on their own, while others may need expert help.

Anthracnose Fungus
Anthracnose is one fungus that causes maple tree leaves to brown prematurely. It can also make the leaves curl up, become distorted, have brown patches across the leaves, and make them drop early.

This fungus typically shows itself in the lower and inner areas of the tree, but it can work its way farther into the higher branches. Wind or splashing water containing anthracnose spores can spread the fungus.

If your maple tree is showing symptoms of this fungus, there’s not much you need to do unless it has infected your tree for a few years in a row, and shows significant leaf damage. When your tree has a prolonged experience with severe anthracnose and shows no signs of getting better, call a tree expert to treat it.

Follow these steps when treating this tree malady; water your trees sufficiently during the growing season, but keep water from splashing onto the leaves. Prune affected branches and leaves, and trim to allow more light to penetrate from the canopy. Then destroy any infected fallen leaves, as well as the trimmed leaves, to prevent the issue from reappearing.

Keep your tree as healthy as possible through this time and it should get better on its own. Just be sure to limit fertilization unless soil tests find the ground lacking in key minerals.

Tar Spot
Tar spot is another fungus that can cause leaves to turn brown, in small circular spots, and then fall off early. This is another non-lethal leaf affliction, especially in larger, established trees.

The spots may start about ⅛ of an inch in diameter, and look yellow or brown, but they can grow a little bitter as it spreads. Aside from giving the leaves an ugly appearance and causing them to fall early, this fungus doesn’t do lasting harm to the tree.

To prevent the spread in the next growing season, rake the leaves up and dispose of them. They can be burned—assuming where you live allows for the burning of leaves—buried, or composted. The compost needs to be warm enough to eradicate the spores if you choose this method.

Make sure your compost pile gets at least 140℉ and you turn the pile frequently to make sure all the leaves get “cooked.”

Fungicides don’t need to be used to treat most cases of tar spot.

Verticillium Wilt
Verticillium wilt is something that can permanently damage a tree as there is very little that can be done about it. This is a soil fungus that enters through the tree’s roots, then prevents water and nutrients from flowing up through the tree to the leaves.

Another problem with this affliction is that it can mimic other less destructive symptoms like scorch. Verticillium wilt can occur at any time during the growing season. It also can show up one year, then lay dormant the next year, but it won’t go away on its own.

Unfortunately, no current fungicides work against verticillium either.

Other symptoms of this fungus include loss of foliage on a single branch, which then stops living. It may infect a whole side of the tree. It can also cause stunted growth, and leaf wilting.

Once it enters the plant, there is no real cure. If the tree is small and new, it is best to remove it and not plant anything in that area until the soil is treated. If the tree is sturdy and established, you can give the tree the best care you can to help it be able to fend the fungus off.

Keep the tree watered well, but not over-watered, fertilize it with a high-phosphorus content fertilizer and remove any branches that are no longer showing signs of life.

You may be able to treat the soil by a process that is called soil solarization. Soil solarization heats the soil using the sun’s heat to burn off bacteria, fungi, insects, nematodes, and other soil pests.

First, remove any grass or plants from the area. Then water the ground well. You want the water to create steam from the hot sun. The heat from the steam is what will rid the soil of the fungus.

Next, cover the area with a thick, preferably clear, plastic. Then bury the perimeter to keep it from blowing off and to keep the humidity and heat inside. Leave the plastic to “bake” for at least four weeks during the hottest days, then remove the plastic.

3. Drought Leads To Thirsty Leaves

Trees going through an extended drought can cause leaves to brown and eventually fall off. While trees are more tolerant than grasses and flowers, they can still succumb to the drying effects of a long dry summer.

Usually, the leaves will wilt when water becomes scarce, followed by a yellowing. If the lack of water continues, then the leaves will brown and eventually fall off.

Some species of maples are more tolerant of drought than others. The sugar maple is one tree that doesn’t do well in either dry or hot environments and will require more watering.

If your area is experiencing less than normal rainfall and the soil is becoming hard and dry, you probably need to water your trees to keep them from dropping their leaves. Watering your trees when the leaves have started wilting can bring them back, but once they turn brown, the leaves won’t get green again.

4. Too Much Water Can Cause Browning

Just as too little water can flip your green leaves to crusty brown, so can too much water. It can be difficult to overwater your trees, especially if you are watering your grass, but in times of extreme rains or floods, this can happen.

If the environment is to blame for dumping too much water onto your trees, there’s not much you can do. You might be able to go out and implore the clouds to move on to other, drier areas, but I doubt they’ll listen.

Too much water from rain most likely won’t permanently ruin your trees. Unless root rot sets in which a strong, established tree can usually overcome in the next season. All you can do is wait for the next growing season to see if the tree comes back or if it needs to be removed.

5. Your Maple Tree Could Be Iron Deficient

Iron is an essential block in the formation of chlorophyll. Since chlorophyll gives plants their green color, when there is a distinct deficiency of iron, the leaves can become discolored.

A mild lack of iron could cause the leaves to turn yellow or white, but if the nutrient is absent for an extended period, then the leaves will transition to bland brown. Since other issues can cause the leaves to change color, the only surefire way to tell if your soil is lacking iron is to do a soil test.

To get extensive soil results such as pH levels, and several nutrients including iron, submit a specimen. Soil tests are available online at https://shop.msu.edu/products/soil-test-mailer?_pos=1&_sid=74ef9fc82&_ss=r. Home soil tests are currently $26.

A severe iron deficiency in your tree could become expensive to treat. If it’s caught in time, you can probably treat it with an iron supplement such as Southern Ag Chelated Liquid Iron. When a tree, especially a large tree, is severely lacking in iron, you may have to get a professional arborist out to treat it.

They may do a deep iron soak by tapping into the soil about two feet and pumping in a liquid supplement, or they might add the mineral directly into the tree. After you rule out insects, water problems, leaf scorch, or fungus, then you might have to resort to iron supplements.

6. Overfeeding Can Lead To Brown Leaves

Spots on the leaves of a diseased maple tree

Adding too much fertilizer can stress the tree and cause more damage than good. In fact, most trees don’t need extra feeding because they get enough nutrients from their vast network of roots. Unless your soil is in terrible condition, tree fertilizers aren’t necessary.

Mulching your grass and leaves into the ground and adding mulch to the base of your trees gives them plenty of nutrients to stay strong and healthy. Testing your soil will let you know if you truly need to add any extra nutrients to your yard.

If you need to add plant food for your trees, be sure to follow the recommended doses so you don’t accidentally feed it too much and cause problems like root rot, slowed growth, and brown leaves.

7. Root Damage Harms Maple Leaves

As well as the rest of the tree. When the roots get damaged, it prevents nutrients from reaching the leaves, which can cause brown leaves.

Most trees, especially big, established specimens, can easily withstand a bit of root damage. When large sections get damaged either by digging, insects, or fungus, the tree can become stressed. If too much of the root system is torn up, then the entire tree might cease to live.

While you will be able to tell while digging if you damaged the roots of a tree, insect damage might be harder to spot. Some insects can bore into a tree and down to its roots, causing damage. This can prevent nutrients and water from reaching the foliage.

To spot insect damage, especially from boring pests, look for small round or D-shaped holes along the base of the tree or around the trunk. You might even see small piles of sawdust on the ground as well.

Insects can damage smaller saplings much faster than mature trees, but a large enough infestation can create serious damage to the mightiest of trees. If you notice boring insects and they seem to cause a lot of harm to your tree, seek the advice of a professional tree service.

You might be able to treat them yourself, but if you don’t get them all, another generation of insects could come back and infect the tree again.

If you do have root damage on your tree, then it may be a good reason to cut down your maple when you have the chance.

The following articles may also be helpful:
https://hgic.clemson.edu/factsheet/maple-diseases-insect-pests/
https://hortsense.cahnrs.wsu.edu/fact-sheet/maple-leaf-scorch/
https://content.ces.ncsu.edu/common-disease-pests-of-maple-in-north-carolina

You may also find it helpful to engage a Certified Arborist to assess the tree and provide a treatment plan. I recommend a Certified Arborist because they must pass a test and must acquire continuing education. You can locate such individuals at http://www.treesaregood.org/findanarborist/findanarborist.aspx