There are a lot of things to love about oak trees. They are tall, beautiful, and very hardy. They can even house hundreds of different species of birds, insects, and other critters. Unfortunately, oak trees can also house many harmful or destructive varieties of fungi.
To prevent fungus from affecting your oak tree, apply mulch, prune your oak during the dormant season, and avoid any injury to the tree that exposes the inner layers. For active oak tree fungus, prune affected branches and apply fungicide.
Reading on further will give you the information to identify, treat, and prevent some of the most common fungi you may see on your oak tree. Some oak tree species are resistant to certain fungus, while others are very vulnerable.
What Does Oak Tree Fungus Look Like?
There are three different ways you can tell if there is a fungus on your tree. The most obvious is seeing mushrooms growing out of the tree or around its base. Fungi may also look like a dusting over the bark
Other signs of fungus invading your tree are unusual growth, discoloration, and wilting of the leaves. The bark may have cankers, scabs, or discoloration as well.
If you notice any of these things, your best bet is to call in a professional. A professional arborist will be able to diagnose and treat the tree properly without all the guessing work on your part.
Fungi is not the only issue your tree may encounter. To educate yourself on the most likely culprits, check out our article: What’s Wrong With My Oak Tree?
How Did My Oak Tree Get Fungus On It?
Your oak tree has fungus on it for a variety of reasons. For starters, fungi is EVERYWHERE. There will always be fungus near your tree. It is a part of the ecosystem.
Fungal spores travel to your tree by wind, rain, improperly cleaned tools, and animal and human movement. Fungus can attach to the bottom of your shoes and travel all over your yard and oak trees as you walk around. The possibilities for spreading fungi are endless.
So instead of wondering how to prevent fungus from coming near your oak tree, since that is impossible, your best bet is to keep the oak tree’s “immune system” as healthy as possible.
Next up is a list of some of the most common types of fungus and what to do about it if your oak tree has it.
Types Of Oak Tree Fungus And How To Prevent And Remove Them
There are a variety of fungi that affect oak trees that mimic each other. This means it is very important to identify which type it is before treating it because there are different treatments for different fungus.
I’ve written some information for you below about the species, identification, ways to cure oak fungus (when possible), and ways to prevent fungus from coming back. You will be more prepared once you are done reading!
Oak anthracnose, or apiognomonia errabunda, is known as a type of leaf spot or leaf blight disease. They love the cool and wet weather of spring.
The effects of the fungus look awful, but luckily the damage never fully eliminates the tree. However, repeated attacks by this fungus will leave your tree vulnerable to other problems.
The fungus begins on the leaves and is dormant during the winter months. Once it warms up a little, the spores release and travel to other leaves.
The fungus will then produce more spores and spread to other leaves until the weather heats up and becomes dry. This will usually slow down or stop the fungus.
Light rain will also increase the spread of the fungus by carrying spores through the droplets that splash up when they hit the ground.
According to the University of Minnesota, you can tell if your oak tree has this fungus through the leaves. The leaf veins will become brown or black and look like they have been scorched.
You will see the leaves of the lower branches of the tree become discolored first. Then it will spread upwards. Young leaves may be distorted or fall off depending on the severity of the anthracnose.
Anthracnose spreading among oak trees is just one of the ways oak trees can cause damage.
How Do I Fix Anthracnose On My Oak Tree?
To stop the fungus from spreading to other parts of the tree, you should properly prune off the affected branches or twigs. Fungicide is not necessary unless it is a long-term probelm. It will do nothing once the leaves have become discolored.
You can prevent oak anthracnose from coming back next year by raking up all the leaves from your yard. The fungus will live and produce spores on the fallen leaves if they are still there come spring.
Ganoderma applanatum or artist’s conk is a decaying fungus affecting any size oak that rots the heartwood of the tree. The heartwood is the most inner part of the tree trunk. As it decays the lowest part of the trunk, the tree becomes a hazard for falling over or being uprooted.
You will know your tree has this fungus if the leaves are yellow, wilted, or smaller than usual. You will also see the mushroom, or conk, grow around tree limbs, the base of the tree, and any exposed roots. The conks grow in shelves that are brown with white or gray edges.
Unfortunately, if you see these mushrooms or cankers appear on your tree, then the death of the tree is coming in 3-5 years. There is no way to cure artist’s conk. The best thing to do is to remove the tree, its roots, and the soil from the area.
How Do I Prevent Artist’s Conk On My Oak Tree?
You can prevent artist’s conk or Ganoderma root rot from making your oak tree its home in three ways:
- Maintain the amount of water your tree gets
- Line the tree with mulch
- Use soil care products to improve the health of the tree will all help protect your tree
Avoid injuring the oak tree as the wound will leave it vulnerable to the fungus.
Armillaria Root Rot
Armillaria root rot is also known as shoestring root rot, mushroom root rot, or toadstool. Armillaria mellea loves wet summers and moist soil and grows quickly when plants are over-watered.
It is parasitic to other plants as well, including lilac and daffodils. It spreads and damages oak trees by the roots. The fungus reaches across to affect neighboring roots. Once it touches the root, it decays the wood and destroys the oak bark by dissolving it.
The first sign of armillaria root rot is when the shoots are stunted, oak leaves become discolored, and an unusual number of leaves fall. Honey-colored mushrooms pop up around the base of the tree during late summer and fall.
If the tree’s root system has been taken over by armillaria fungus, then you should remove the oak tree and its stump immediately, or else you will spread it to other plants.
How Do I Prevent Armillaria Root Rot On My Oak Tree?
To prevent this from taking over your oak trees and landscape, you should first make sure you are not over-watering them. Check your oak trees often for signs of ailments.
Do not plant one of the host plants in your yard either. You create a breeding ground for the fungus to grow and spread that way.
Fungi will grow easier on stressed-out trees. Reduce oak tree stress by mulching around the tree (only 2-3 inches high), taking care not to wound the tree with lawn tools, avoiding over-watering, and pruning in the dormant season. This is the best way to keep this fungus at bay!
Check out our piece Best Time To Trim Oak Trees + Trimming Calendar And Tips to learn more about proper pruning! It is a very important step to keeping your tree healthy.
Sudden Oak Death
This type of fungus is known as Phytophthora ramorum formed by a water mold. It is known for the mass damage it has caused to oaks along the West coast.
It even affects other plants like rhododendron and around one hundred other species. According to the Ohio State University, it was introduced to the country through rhododendrons sold in retail stores. Crazy!
Any plant hosting this oak tree fungus planted six feet or less from an oak tree may be affected. There is not a lot of evidence explaining how the fungus spreads, but scientists guess it is spread through rain, wind, and humans or animals as they travel through forests.
If you have white oaks, have no fear! Only red and intermediate oaks can be affected by this fungus.
How Do I Know My Oak Tree Has Sudden Oak Death?
It is a little difficult to identify sudden oak death because it mimics a lot of other oak tree afflictions.
You should keep an eye out for trunk cankers, which look like red-brown or black wounds oozing red or amber sap. You will see these cankers anywhere from 4 to 6 feet above the soil line.
Some other signs of sudden oak death are leaf loss over time or sudden browning and falling of leaves. It can take 2 years or less for the oak to perish.
Unfortunately, there is no cure for sudden oak death. You can use a fungicide to lighten the symptoms, but it will just delay the inevitable.
If you think your tree has this, call a local arborist as soon as possible to diagnose and prevent spread.
What Do I Do If My Oak Tree Has Sudden Oak Death?
If your tree has sudden oak death, you can either delay it from happening or remove the tree altogether.
If you are delaying it and want to enjoy your oak longer, immediately prune any affected branches. Spray the cankers and other affected areas with fungicide.
When you prune, sanitize the pruning tools you used with bleach to prevent the spread.
I recommend using the Reliant Systemic Fungicide (Agri-Fos/Garden Phos) on your tree to extend its life because it has phosphonate, which is very effective against this specific fungus. Some experts suggest using a fungicide injection to put into the trunk.
You should also put mulch around the tree (2 to 3 inches high) and fertilize it. Do not let the area get too wet, there should be good drainage.
However, the best choice for dealing with an affected tree is to cut it down. Eventually, it will become a falling risk.
Then, check the plants in the area for symptoms. Spray the phosphonate fungicide around host plants and trees, but only if the affliction is present already. Paying attention to your oak is key to stopping the spread of the fungus to other trees.
Oak Leaf Blister
Oak leaf blister, also known as taphrina caerulescens, commonly affects many oak tree species. Red oaks are notorious for this fungus! You’ll see oak leaf blister in the spring during cool, wet weather.
Oak leaf blister spreads by wind and rain onto buds and twigs of the tree. It will lay dormant in the winter and grow when the spring hits and new leaves have sprouted.
You will notice this fungus on the leaves of oak trees in early summer as raised greenish-yellow spots on the top and gray depressions underneath. The leaf will then turn red or brow
Luckily, this fungus does not full eliminate injured oak trees. Instead, it deforms the appearance of the oak tree with discolored leaves.
How Do I Prevent Oak Leaf Blister On My Oak Tree?
Preventing oak leaf blister is quite easy. Apply a pesticide to the buds of the tree in early spring and it will keep it at bay. Fungicides do not work on this affliction if you use it after the buds have broken open.
Only use this method if you are dealing with a small tree. I strongly recommend hiring a professional if you are applying pesticide to a large tree. It is a very laborious and dangerous job, so consider your safety when deciding how to treat your tree.
Oak wilt, scientifically known as ceratocystis fagacearum, is a oak tree fungal affliction that was discovered in red oak trees 77 years ago and affects trees in over twenty states. It can affect every species of oak tree, but white oaks are more resistant to oak wilt than red oaks.
The fungus spreads through the roots of the oak tree and by sap beetles that feed on it.
Wilted, dull green, or brown oak leaves are the first sign of oak wilt, which is similar to drought-affected trees. Every color of leaves will have fallen at the tips of the branches. In some oaks, you will see brown streaks underneath the bark.
Once affected, red oak trees can parish as little as weeks later, while white oaks can last one to a few years after the fungus.
The most important thing you should do to stop oak wilt in its tracks is remove the affected tree from your yard. Do this before the beetles or roots can spread it to other trees.
How Do I Prevent Oak Wilt On My Oak Tree?
The most effective way to prevent oak wilt is to avoid pruning the tree once the spring temperatures reach 50 degrees. Sap beetles become active when it gets warm and fungi create fruiting structures, so the oak affliction spreads quickly when it is warmer.
Once you wound the tree by pruning, paint over the exposed areas with tree-wound paint so the beetles can’t get to the sap as easily.
You can do a lot of the steps above on your own, but the best option for inspecting, treating, and preventing fungi from invading your oak trees is to call a professional. They will take out any hassle or confusion when figuring out what is wrong with your tree.
Make sure your yard is free of fallen leaves and branches and affected, tree stumps. Many fungi will survive year after year if left unchecked, so follow the tips above to keep the annoying fungus from invading your oak trees.
If you’re interested, take a look at our guide: 10 Early Symptoms of a Dying Oak Tree: Prevention Guide to learn more about saving your oak tree!
Go forth and good luck!
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Koetter, Rebecca, and Michelle Grabowski. “Anthracnose of Shade Trees.” Lawn and Garden, UMN Extension, 2018.
Frankel, Susan J. “Sudden oak death and Phytophthora ramorum in the USA: a management challenge.” Australasian Plant Pathology 37.1 (2008): 19-25.
Popenoe, Juanita, et al. “Key Plant, Key Pests: Oak (Quercus spp.): ENH1332/EP596, 12/2020.” EDIS 2020.6 (2020).
Smith. “Rhododendron Plants, Walmart, Rural King and Sudden Oak Death!” Fairfield County Master Gardeners, The Ohio State University, 18 July 2019.
Southworth, Darlene. “Oaks and mycorrhizal fungi.” Oak: Ecology, types and management (2013): 207-218.