We love the vibrant colors of maple trees in the fall. These deciduous beauties bring not only great color but also a recognizable leaf shape and (our favorite) whirlybird seeds that helicopter their way to the ground. So naturally, we want to protect these gorgeous trees at all costs by keeping them free from disease. To keep your maple trees healthy, learn how to spot maple tree diseases and find out what to do about them.
Common Maple Tree Diseases
Hopefully, your beloved maple tree will never be struck with disease. But if they are, you can start your diagnosis with these common maple tree diseases.
- Maple wilt
- Anthracnose
- Tar spot
- Sapstreak
- Phyllosticta
- Powdery mildew
- Scorch
Maple Wilt
One of the most common maple tree diseases is maple wilt, which is caused by soil fungi called Verticillium albo-atrum or Verticillium dahliae. Be on the lookout, as the problem can be serious and even kill established trees.
What to Look For
A tree with maple wilt may have browning or scorched-looking leaves, and diseased branches will have small amounts of sick-looking leaves. Sometimes olive-colored streaks will be found in the sapwood of an affected tree. Cut the bark and look for these streaks, then take the bark to your county Extension Office for confirmation.
How It Spreads
The disease starts in the root system and spreads up through the sapwood into the upper branches of the tree, causing big limbs to start dying.
Prevention
A healthy, vigorous, well-established tree may be able to beat maple wilt, but most trees will die within a season or two of showing symptoms. Unfortunately, the best way to control the disease is to destroy infected trees to prevent it from spreading. If that's not an option, or the tree is not seriously infected, pruning out affected branches may help the tree survive. Keep the tree well-watered while it's trying to heal.
The disease is most common in Norway maples, but it's also found in silver, sugar, red, sycamore, and Japanese maples.
Related: How to Save a Tree With Damaged Bark
Anthracnose
Anthracnose (Colletotrichum gloeosporioides) is a group of diseases caused by fungi. It can affect many shade trees. Similar fungi attack other trees such as sycamore, white oak, elm, and dogwood trees. They cause a loss of leaves and are usually relatively harmless when the disease only strikes once.
What to Look For
This type of fungus is particularly common after unusually cool, wet winters and can affect bud formation, kill small twigs and leaves, or cause premature and repeated early leaf loss. On maple trees, it causes brown or purplish-brown spots and stripes near the veins on the leaves. The tree may lose its leaves prematurely. If the disease cycle repeats year after year, the tree may become stunted or deformed because it can't keep its leaves long enough to grow.
How It Spreads
Anthracnose spreads by airborne fungus and is especially prevalent during a wet or rainy spring. In maple trees, it's spread in April or May in most gardening zones. The wind blows through the infected trees and spreads spores onto new maple trees. Wet springs provide the ideal conditions for anthracnose spores to take hold.
Prevention
It's important to rake up all the fallen leaves each fall and compost or burn them (if your area permits burning). Fallen leaves provide the ideal breeding ground for anthracnose. Another option is to have an arborist spray the trees with a special fungicide containing mancozeb. If the damage continues year after year, it could predispose the tree to other problems.
Tar Spot
Another common maple tree leaf disease is tar spot, which can be caused by one of two different fungi: R. punctatum or Rhytisma acerinum.
What to Look For
Tar spot is an ugly but mostly harmless disease that strikes several maple species. As its name implies, tar spot disease looks like big black tar spots on the top of the leaves.
How It Spreads
Infection typically begins in early spring and continues into the early summer. The fungus is able to take hold when there are prolonged periods of wet weather that prevent the leaves from drying off. Leaf spots start out yellow and evolve into a dark, tar color.
Prevention
Treatment is generally not recommended for tar spot because it is usually not a serious problem; however, raking up fallen leaves will keep tar spot at bay.
Sapstreak
Sapstreak (Ceratocystis coerulescens (C. virescens)) is a fungal disease that affects sugar maples. It's a fatal disease that discolors the wood, so salvage is not possible. This disease is mostly seen in parts of North Carolina, Michigan, Wisconsin, and Vermont.
What to Look For
The disease causes foliage at the crown of the tree to become smaller, and bald spots often appear.
How It Spreads
Over time, this dwarfing spreads, and the tree ultimately dies. When the tree is cut down, a radiating pattern will be seen in the wood of the lower part of the tree.
Prevention
The only way to get rid of sapstreak is to cut down the tree as soon as possible after noticing the problem. Sapstreak can spread with the help of insects through wounds on the trees, so removing infected trees is important to keep other trees healthy if you have multiple maples.
Phyllosticta
Like anthracnose, phyllosticta leaf spot (phyllosticta minima) is caused by a fungus.
What to Look For
Phyllosticta causes raised tan or dark brown leaf spots. The spots may turn dry and brittle and crumble away, leaving holes in the maple leaves.
How It Spreads
As with anthracnose, the fungus that causes phyllosticta spends its winters hiding among fallen leaves on the ground. It waits until the spring when damp conditions give it the opportunity to spread. Breezes carry the spores to new hosts.
Prevention
Rake up fallen leaves each autumn and discard them properly to prevent fungal diseases such as phyllosticta.
Powdery Mildew
Powdery mildew, which can be caused by several different fungi, dulls the appearance of maple leaves (and that of many other plants as well), but it isn't life-threatening.
What to Look For
If you notice your maple leaves are looking dull instead of bright green or have a powdery white substance or spots on them, it's probably powdery mildew.
How It Spreads
Powdery mildew tends to happen in very humid locations, and the spores spread on the wind.
Prevention
You can't do much about relative humidity where you live, but you can avoid overwatering your tree and surrounding landscape, which can create a damp environment in which powdery mildew thrives. You should also rake up any leaves or other debris so it doesn't have a damp spot to take hold.
Scorch
Leaf scorch isn't so much a disease as it is damage to the tree that occurs in the hot summer months when the temperature is high and the precipitation is low. It can damage trees that are already unhealthy, but it won't do irreversible harm to healthy maples.
What to Look For
You'll notice browning around the edges of the leaves and yellowing between the leaf veins. This usually occurs during the hottest months of the year (July and August).
How It Spreads
Leaf scorch doesn't spread from tree to tree, but it spreads throughout a tree when it's very hot, and the soil around the tree doesn't have enough water either due to drought or insect damage.
Prevention
Following the right watering routine can help prevent scorch. You should begin your watering regimen in the winter, soaking the roots about once a month when it's not icy or snowing, and continue watering deeply about once a month all year long. Don't water more often if scorch occurs — simply maintain your watering routine, allowing the soil to dry out between waterings.
Preventing Maple Tree Diseases
The best thing you can do to protect your trees from maple tree disease is to take good care of them before they develop a disease. That means watering them regularly, fertilizing them annually, keeping the area around the trees clean, pruning when necessary, and seeking help immediately if you notice your tree looking ill or having problems.
