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  • Writer's pictureMedrano's Tree Service

Oak Tree Health in the City: How To Tell an Oak Tree Is Dying and What to Do

In an urban environment, oak trees provide valuable shade, greenery, and wildlife habitat. They are moderate water users and generally low maintenance. But like any other living thing, oak trees do sometimes get sick and die. However, if you know what to look for and what to do about it, an oak tree can be saved to provide many more years of beauty.


So today we’re taking a look at both the signs of an oak tree dying, what kills an oak tree, and how to save a dying oak tree.


Symptoms: How to Tell if an Oak Tree is Dying

Before an oak tree is dead, it has to go through the process of dying. In many cases, if caught early enough and addressed the right way, a dying oak tree can be brought back from the brink to provide beauty for many more years.


Here are the signs of an oak tree dying:




  • Cracked bark or bark falling off

  • Yellow or brown discolored leaves

  • Out-of-season leaf drop

  • Delayed leaf production

  • Stunted leaves

  • Oozing sap

  • Holes or cankers in bark

  • Dying branches or branch tips

  • Dropped branches

  • Holes from boring insects



Three things are generally responsible for oak tree death: compromised bark, insect infestations, and oak tree diseases such as bacteria and fungus. We’re going to take a look at the signs and solutions for each of these problems.


Cracked or Peeling Bark


One of the easiest-to-spot symptoms of a distressed oak tree is cracked or falling-off bark. Cracked bark on oak trees is primarily caused by environmental issues, not disease or pests. 


What causes oak bark to crack or fall off? Long periods of inadequate watering will sometimes cause shrinkage in the live wood beneath the bark, creating a crack in the outer bark. This dehydration is usually paired with the death of one or more branches, as the tree works to conserve resources. 


On the other hand, a tree trunk planted by grass that is constantly wet from lawn sprinklers will start to rot and peel from the moisture. This rot is dangerous, since it can eventually spread to the living wood and slowly kill the tree.


Another common culprit of cracked bark on oak trees is temperature! In wintertime, the bark on the south-facing side of the tree trunk often experiences large temperature swings from the cold nights followed by the warmer days. When the sun’s rays hit the trunk and heat it even more, the bark experiences a freeze-thaw cycle where tissues contract in the cold but expand in the heat. This often results in cracked outer bark and sometimes even cracked inner wood.


Lastly, mechanical damage from lawnmowers, weed whackers, heavy machinery, and car accidents can crack bark and cause it to separate from the cambium.


Cracked bark is different from a bark canker, which is a symptom of bacterial and fungal disease, which we will also cover later in this article.



Solutions for Cracked or Peeling Bark


If the oak tree bark is cracked from a lack of water, more frequent and deeper watering will help it recover from the stress of dehydration. The bark itself is not able to heal, but the live wood beneath should be able to create a seal to keep out moisture and insects.


If the bark falling off your oak tree came from too much water sprayed on the trunk, immediately adjust your sprinklers to redirect the spray away from the trunk. Remove rotten or tenuously attached bark so that moisture, fungus, or bacteria don’t build up against the living wood. 


Oak trees that are affected from the freeze-thaw cycle benefit from tree wrap in the wintertime. This is simply white fabric, plastic, or paint applied to the trunk in the wintertime. The color white reflects sunlight instead of absorbing it, allowing the tissue of the bark to maintain an even temperature instead of freezing and thawing. 


In cases of  mechanical damage, the inner wood should be regularly inspected for fungus, insects, or disease, and protected from sunscald in the same way with a white paint or covering.


Do not use sealant on the cracked bark! This is more likely to seal in fungus and bacteria than it is to seal them out. Instead, provide care to your oak tree to prevent stress and support its natural defense mechanisms. A certified arborist can help you determine what your specific oak tree needs to thrive.



Insect Infestations


An oak tree can also be badly affected by boring insects. These pests often take advantage of a stressed or damaged tree to burrow into the heartwood, where they  feed on the tissues as adults and larvae, and hollow out chambers to lay eggs in. They can cause enough damage to compromise the living tissues of the tree that carry water and nutrients between the crown and the root, as well as making it more susceptible to bacteria, fungus, and disease.


The telltale sign of borer activity on a dying oak tree are the small round entry and exit holes that the adults and larvae make in the outer bark. You may also be able to spot sawdust around or beneath these holes.


Secondary signs include branch and crown dieback, wilted or discolored foliage, and increased squirrel and bird (especially woodpecker) activity.


Solutions for Insect Infestations


Infestations can be difficult to treat, and often it takes a couple of seasons to get a dying oak tree back to full health. 


The infested tree can be treated with a pyrethroid spray to kill off the existing population of borers, followed by a systemic root drench to prevent recurring infestation. Some of these chemicals need to be applied by a certified pesticide applicator. It’s also wise to prune out any dead or heavily infested branches.


The best treatment for insects is prevention: a healthy tree will be better able to fend off and recover from an infestation. Make sure your oak tree gets the water and nutrients it needs, and doesn’t suffer mechanical damage to its roots or bark.


Oak Tree Diseases


Oak trees can be affected by bacterial and fungal diseases, all of which create leaf discoloration and sometimes leaf drop. This is a non-exhaustive list of some of the most common culprits:


Oak Leaf Blister: caused by the fungus Taphrina caerulescens; creates light green or yellow “blisters” on leaves. Oak leaf blister is usually mild and needs no treatment other than clearing each year’s leaves to remove overwintering spores.


Bacterial Leaf Scorch: caused by bacterium Xylella fastidiosa, which attacks the xylem of the tree and limits its ability to transport water. Leaf edges become red or yellow, then the entire oak leaf will brown and drop. Often followed by dieback of the entire branch.


Actinopelte Leaf Spot: Tubakia dryina (formerly called Actinopelte dryina), and most problematic in chronic wet weather. This fungus creates dark or reddish leaf spots ¼ to ½ inch in diameter, leading to leaf drop.


Powdery Mildew: caused by several fungi (Erysiphe trina, Microsphaera alni, Phyllactinia corylea, and or Sphaerotheca lanestris) which form a powdery layer on leaf surfaces. Sometimes results in malformed foliage or dropped leaves, but is often a purely cosmetic issue.


Armillaria Root Rot: caused by the fungus Armillaria mellea, which thrives in wet soil conditions and decomposing wood. Oak trees dying from root rot experience a slow decline, with limbs dying off gradually. Armillaria sometimes forms honey-colored mushrooms on the soil surface following the outline of the major roots.


Sudden Oak Death: caused by fungus Phytophthora ramorum, which infects the bark tissue, kills the cambium around the tree, cutting off the crown from the roots and causing both to quickly die. Sudden oak death is hard to diagnose before it has killed the tree.


Solutions for Oak Tree Diseases


Oak tree diseases typically present fairly mildly, and then become more entrenched over several seasons as the bacteria or fungus spreads. Clear last season’s leaves from around your oak trees to prevent spores or bacterium on these fallen leaves from re-inoculating your trees in the spring. 


Bacteria can also be spread by leafhopper and spittlebugs, so keep an eye out for these bugs on nearby weeds or shrubs. 


Fungus on oak trees is almost always a result of frequent wet weather, which we can’t control, or overwatering, which we can! Oak trees don’t like having “wet feet” or constantly wet soil, so time your waterings to allow the first three to five inches to dry out.


Correct watering and fertilization will help prolong the life of a diseased tree, and antibiotic infections or sprays can help some trees with some diseases. But when it comes to bacterial leaf scorch and armillaria root rot, the oak tree will simply decline over five to ten years. However, pruning and trimming can keep a declining tree from becoming a hazard and keep it alive as long as possible. You can work with a certified arborist to get a positive identification of your oak tree disease, then form a treatment plan specific to your tree and its problems.


How Long Does an Oak Tree Live For?


Oaks are among the longest lived deciduous trees. One tree in Italy has lived to be about 1,000 years old! But how long an oak tree will live is dependent on its species as well as its conditions. A white oak can live up to 600 years, while a laurel oak may only make it to 60. Most oak species can make it to 150 years old–even oaks that deal with damage, pests, or disease.


If you think your oak tree might be dying or distressed, Medrano’s Tree Service can help. Call (919)3573376- today to schedule a consultation and treatment plan tailored to you and your trees!







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