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Past Articles Library | Trees | How to Diagnose and Treat Common Oak Tree Diseases


While there are numerous plant diseases that can hit any of the 60 varieties of oak tree, a few of the more common ones will be covered.  Below is a description of what the plant disease looks like and what you can do about it.

Diseases of the Leaves and Twigs (Fungus)

When looking to diagnose a plant disease, a good start is to look at the leaves.  This can tell you a lot about the health of the tree. 

Oak Tree Blister

This plant disease can be seen on the top and bottom of the leaves.  On the surface of the leaf, you will see blister like areas that can be as big as a quarter.  On the other side of the leaf, one will find a gray colored depression that matches up with the blister.  As the disease progresses on this leaf, the blister will turn brown, the leaf will curl up and eventually the leaf will drop prematurely.  While this disease does not cause the tree to die, it does make it look unsightly.

The causes of this disease are environmental.  It takes a combination of factors for this disease to take off even though it can be stored in the twigs and buds of the oak tree.  To encourage the growth of this disease, the weather must be unseasonably mild, wet, and humid in the spring.  If these environmental factors play out in your area and you or a neighbor has an existing case of oak tree blister, you will probably develop the disease in your remaining oaks.  Why is this?  The reason is that the spores are easily transported through wind and rain. 

To reduce the chances of getting this plant disease or to control it, only requires one simple step and that is to clean up the garden space.  Remove all the fallen leaves and throw away.  If you have had oak tree blister, do not compost the leaves.  The spores will remain in the compost and when you go to use it, you will be reincorporating the spores back into the environment. 

Anthracnose

This plant disease typically hits new shoots and twigs.  It can be seen as browning of leaves and twigs that eventually die back.  Or, this disease can be seen as cupping and browning along the leaf veins in slightly older leaves.   Mature leaves are typically not affected.

Another characteristic of this disease is the presence of small fruiting bodies on the underside of affected leaves.  These fruiting bodies normally follow the vein of the leaf. 

This fungal disease survives in twigs and plant debris.  It also loves mild winters by which it can remain active.  Wind and rain are means by which anthracnose spreads from one twig or branch to another. 

While your tree my look untidy, this plant disease is normally not fatal.  To reduce the chances of developing this problem or treating an already existing case of anthracnose, one must make sure that the tree is being properly feed.  Next, one will need to prune back the lower branches of the oak tree.  This will increase air circulation around the branches, which will help dry out the immediate environment around the tree.  All funguses like moist environments and doing the later step will reduce that moisture.  Lastly, one will need to rake up all the leaves and twigs that have fallen.  Dispose of the leaves by placing them in the trash or burning them. 


Tubakia Leaf Spot

This oak tree disease appears as brown to reddish brown blotches on young leaves.  On older leaves, the tubakia leaf spot appears as spots of dead leaf tissue.   Fungal fruiting bodies can be seen on top of these lesions.   If the tubakia leaf spot sets up on or along the veins of the leaf, the leaf itself will cave in due to the blockage of water up and through the vein.

If winters are mild, this fungus can live in twig and leaf debris.  It thrives in areas that are wet, warm and humid.  While both red and white oaks can get this disease, the red oak is more susceptible. 

If you happen to find this in your oak, do not fret.  It is easy to treat with a few simple steps.  First, make sure your oak is in good health.  What does this mean?  Well, you need to make sure that your oak is receiving proper nutrition through a fertilizer program along with enough water.  Next, you will need to improve air circulation around the tree.  This is done by pruning back the lower branches.  Finally, clean up underneath the tree and dispose of the leaves and twigs in the trash.  This last step will reduce the chances of a reinfestation of the fungus. 

Powdery Mildew

This plant disease can occur in other plants besides oaks.  The common characteristic of the disease is a white, powdery growth on the top of the leaves.  During the late summer to fall, one can also see small, black fruiting bodies growing up through the powdery growth.  If the infection attacks buds and/or shoots, the growth will be more like the leaves of a holly, which is long and pointy. 

A cool, moist spring is a wonderful environment for powdery mildew.  It survives in the leaf debris left from the fall.  Wind can spread the spores to new vegetation but they will only take hold on dry leaves. 

To reduce your chances of developing this problem, remove any fallen leaves and/or twigs.  Water only in the morning and prune away any deformed branches and/or leaves.    

Insect Caused Oak Tree Diseases

Bacterial Leaf Scorch

This disease is carried by leafhoppers and spittlebugs.  It can also be transferred through contact with other oak roots.  The symptom of this disease mimics plant stress due to lack of water or drought conditions.  Oak leaves will turn brown along the edges in response to any drought but what separates plant stress from disease is a reddish or yellow border between the brown leaf margin and the green portion of the leaf. 

Once you have proper diagnosis of bacterial leaf scorch, you will need to remove the effected tree.  Oaks do not recover from this plant disease and while the scorching on the leaves may be minor it will continue to spread throughout the tree.

After the tree is taken down, replace the oak with a bacterial leaf scorch resistant variety.   Also, keep weeds at bay.  This will keep insect populations down.  Finally, set up a fertilization and irrigation program that will enhance the health of your tree. 

Oak Wilt

This disease starts in the top of the tree and appears as a brown and/or bronzing of the leaves along the margins.  This discoloration continues toward the center of the leaf until the leaf dies prematurely.   This dieback of the leaves will continue down the tree until the tree is dead.  This can occur as quickly as four weeks to a few years. 

This oak tree disease is spread through root grafts and oak bark beetles.  While it can live in leaf litter, if the environment gets above 90 degrees Fahrenheit the disease is killed. 

To control this disease, one will need to cut the tree down.  Trenching is suggested around oak trees so that root grafting cannot occur. 

Fusiform Rust

This disease is not caused by an insect instead it is caused by other trees.  These trees are the loblolly and stash pines.  The symptoms on an oak are orange to yellow pustules that appear on the lower branches during the summer and fall.  It can cause premature leaf drop and an unsightly appearance but it will not kill the tree. 

The process of this disease starts in the spring when pine galls open up and release spores.  These spores are carried by the wind to oak trees.  Pustules on the underside of the leaf open up in the late spring and release spores that are carried to pines.  Once in pines, the spores attack the new growth.  

There really is not control except making sure that there are no pines in your local area.



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