10 Oak Tree Diseases: Causes, Symptoms, Prevention, And Treatment

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Like almost all species of trees, oak trees can suffer from various diseases and pests.

Oak trees commonly face a range of diseases and issues, including Oak Wilt, a fungal disease that causes wilting and browning of leaves; Sudden Oak Death, which results in cankers and sap bleeding; Oak Anthracnose, characterized by dark spots on leaves; Bacterial Leaf Scorch, leading to scorched leaf edges; and Galls, abnormal growths caused by insects or mites.

On top of this, environmental stresses, pests like borers, and other fungal diseases can also contribute to their decline. Before getting out your chainsaw and cutting down a sick oak, learn more about these diseases and whether or not they are fatal for oak trees.

Oak Tree Sickness

oak tree diseases
Image: @nynjtc_conservationdogs

Most oak tree diseases and sicknesses can be easily observed, but some require specialist detection.

For example, this account shared:

…Our oak wilt project, piloted in 2019! We look forward to checking suspicious trees in the Hudson valley and continuing our understanding of dogs’ abilities to detect this tree disease. It’s one of our most challenging, but most exciting projects.

These are the primary reasons an oak tree may appear sickly:

1. Oak Wilt

picture of oak tree wilt
Image: @minnesotadnr
  • Cause: A fungal disease caused by Bretziella fagacearum.
  • Symptoms: Wilting leaves turning bronze, branch dieback, fungal mats under the bark.
  • Prevention & Treatment: Avoid pruning oaks during the active growing season when fungal spores are most prevalent. If an infection is confirmed, remove and properly dispose of the affected tree to prevent further spread. There are also fungicide treatments, but they may be expensive and their effectiveness varies.

This disease is particularly virulent in the Midwest of the United States. While all oaks are susceptible, red oaks are often hit hardest and can die within weeks of infection. Sap-feeding beetles play a significant role in its transmission as they carry spores from infected to healthy trees.

2. Sudden Oak Death (SOD)

what is sudden oak death
Image: @tree_source_
  • Cause: A disease caused by the pathogen Phytophthora ramorum.
  • Symptoms: Cankers on the trunk, bleeding sap, browning leaves.
  • Prevention & Treatment: Sanitation and quarantine are vital. Infected material should be removed and destroyed. There’s no known cure once a tree is infected.

First identified in California in the late 1990s, SOD has wreaked havoc on oak populations along the West Coast. Coastal conditions with moist environments provide a prime breeding ground for the pathogen, Phytophthora ramorum, which affects more than just oaks.

3. Oak Anthracnose

Oak Anthracnose pictures
Image: @wisdatcp
  • Cause: Caused by several species of fungi.
  • Symptoms: Dark spots or blotches on leaves, premature leaf drop.
  • Prevention & Treatment: Rake and dispose of fallen leaves. Fungicide applications can help, especially when done early in the season.

Although often considered a cosmetic issue because it primarily affects the appearance of leaves, severe infections can weaken the tree over time. The disease thrives in wet spring conditions, with new infections often originating from old leaf litter.

4. Bacterial Leaf Scorch

bacterial leaf scorch oak trees
Image: @candide08
  • Cause: Bacteria transmitted by leafhoppers and treehoppers.
  • Symptoms: Scorched-looking leaf edges, branch dieback.
  • Prevention & Treatment: Reduce stress on the tree and maintain its health. There’s no cure, but infected trees can sometimes survive for many years.

Unlike many tree ailments caused by fungi, this is bacterial in nature. Over time, it can cause significant decline and dieback, especially when trees are exposed to additional stresses like drought.

5. Galls

oak tree galls
Image: @redrubyrose
  • Cause: Various insects or mites.
  • Symptoms: Round growths or bulges on leaves, twigs, or branches.
  • Prevention & Treatment: Most galls are harmless. For severe infestations, consider insecticidal treatments.

Galls are the result of specific insects or mites stimulating the tree to produce abnormal growths. The type of gall often indicates the particular pest responsible. For instance, oak apple galls are large, round, and spongy, formed due to a wasp species.

The account that shared the image above said:

Oak galls form when the gall wasp larvae secrete chemicals that induce their growth. The larvae then has its own spherical gall home and chews its way out when hatched (you can see the holes in some of the galls where they’ve made their escape). These wasps are part of the biodiversity of a healthy oak tree with little or no impact on the tree’s health.

From a dyeing perspective, they have been used for millennia for colouring fabric, creating high-quality ink and in the process of tanning leather. The galls have a high tannin content without the same intensity of colour as other parts of the plant such as acorns, so they can be used in the mordanting process and also for the reaction with iron which turns the beige/brown to deep inky greys and black.

6. Oak Decline

why is oak tree dying
Image: @kewarborists
  • Cause: Combination of factors like drought, pests, and age.
  • Symptoms: Gradual dieback of branches, thinning canopy, reduced vigor.
  • Prevention & Treatment: Maintain tree health, provide water during dry periods, and manage pests.

A term that encapsulates a range of symptoms without a single causative agent, oak decline often results from a combination of factors including pests, diseases, and environmental stresses, especially in older trees.

7. Armillaria Root Rot

oak tree fungus root rot
Image: @seilundbeil
  • Cause: Fungus Armillaria mellea.
  • Symptoms: Yellowing or wilting leaves, reduced growth, mushrooms at the base.
  • Prevention & Treatment: Ensure proper drainage, avoid wounding the tree, and remove affected trees.

Also known as “oak root fungus” or “honey fungus,” this pathogen manifests as honey-colored mushrooms at the base of the tree. It’s not exclusive to oaks and can attack other woody plants, spreading through the soil and infecting neighboring trees.

8. Canker Diseases

cankers on oak tree trunk
Image: @50woodsidecottage
  • Cause: Various fungi.
  • Symptoms: Sunken or swollen areas on branches or trunk, dieback.
  • Prevention & Treatment: Prune and destroy affected branches, avoid injuring the tree, and maintain good tree health.

These diseases cause localized dead areas on the trunk, branches, or twigs. The infected areas might ooze sap or cause the bark to crack open. Different fungi cause canker diseases, and their severity can vary based on the specific pathogen and tree’s health.

9. Borers

borer in oak tree
Image: @irconservancy
  • Cause: Various insect larvae.
  • Symptoms: Exit holes in the bark, sawdust-like frass, branch dieback.
  • Prevention & Treatment: Maintain tree health, use insecticides if infestation is severe.

These are not a disease but a group of insects that burrow into the trunk, branches, or roots of oak trees. Examples include the two-lined chestnut borer and the oak borer. Their larvae feed on the tree’s inner bark, disrupting the flow of nutrients and water.

10. Oak Leaf Blister

oak leaf blister pictures
Image: @txplantclinic
  • Cause: Fungus Taphrina caerulescens.
  • Symptoms: Raised spots or blisters on the upper leaf surface.
  • Prevention & Treatment: Fungicide applications can help, especially when done early in the season.

This fungal disease is characterized by raised blisters on the upper surface of leaves, giving them a blistered appearance. While mostly an aesthetic concern, severe infections can lead to early leaf drop, but the tree’s overall health usually remains unaffected.

Prevention and Care

Maintaining overall tree health is the best defense against most diseases. This includes:

  • Proper watering.
  • Mulching to conserve moisture and improve soil health.
  • Pruning during the dormant season.
  • Regular inspections for early detection of problems.
  • Consulting with arborists or local extension offices for specific regional advice.

Once an oak tree gets sick, treatment effectiveness varies depending on the disease. In some cases, the best approach may be to remove and replace the tree, especially if it becomes a threat to nearby healthy trees.

Diseased Or Sick Oak Firewood

You can use sickly oak tree wood for firewood, but there are a few considerations and precautions to keep in mind.

1. Drying

Like all firewood, oak from a sickly tree should be properly seasoned, which means allowing it to dry for at least a year (often longer for dense woods like oak) before burning. Seasoning reduces moisture content, making the wood burn more efficiently.

2. Disease Transmission

If the oak tree was sickly due to a contagious disease like Oak Wilt, it’s crucial to avoid transporting the wood to new areas where it might spread the disease. Fungal mats from oak wilt, for example, can attract beetles which can then transport the disease to healthy trees.

3. Pests

Ensure the wood doesn’t have active pest infestations, like borers. If it does, burning the wood is a good way to destroy the pests, but again, avoid transporting infested wood to new areas.

4. Safe Burning

Even if the wood comes from a diseased tree, when burned, the high temperatures will neutralize most pathogens. However, always burn firewood in a controlled environment, such as a fireplace or wood stove.

5. Storage

If you’re storing the wood before burning, keep it away from healthy trees to minimize the risk of disease or pest spread.

6. Disposal of Waste

After burning, it’s good practice to clean out the fireplace or wood stove and properly dispose of the ashes, especially if the tree had a contagious disease.

While it’s generally safe to use diseased oak tree for firewood, it’s essential to take precautions to prevent the spread of diseases or pests. If unsure about the nature of the disease or the safety of using the wood, consulting with local forestry experts or arborists can provide clarity.

Problems With Oak Trees

oak tree sickness disease

Not everything that, at first, looks like a problem with oak trees, is a problem with oak trees. For example, the image above.

The account, @manorgardener, shared:

Inside each of these tiny silk-button spangles is a baby wasp!

The leaves of this Oak tree have become a nursery for the larva of a Gall wasp (Neuroterus numismalis). At first glance on a grey day this phenomenon may be interpreted as some sort of leaf disease, but wait for the sun to come out and allow the galls the courtesy of an up close study, and you will see neatly combed silky hairs of shining gold!

The gall drops to the ground (as pictured) after reaching a certain maturity, where it’ll remain overwinter to hatch out next Spring as an adult Wasp so minuscule you might mistake it for a Gnat!

So it is worth checking pictures of oak tree diseases, pests, and fungi before thinking the worst. Let us know if you have any questions down below!


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1 thought on “10 Oak Tree Diseases: Causes, Symptoms, Prevention, And Treatment”

  1. Most of the trees are Jack Oak and inside is hollow with black and look like lightening struck but all are like that


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