Common Oak Tree Diseases of the Leaves and Twigs

The oak tree is a versatile plant. It provides shade, acts as a windbreak and produces acorns, which, in turn, feed wildlife. Unfortunately, the mighty oak is subject to some diseases. Some oak tree diseases are nothing more than mild annoyances while others can cause the death of the tree. In this article, we’ll focus on oak tree diseases that affect the leaves and twigs.

Oak Tree Blister

You can see this disease on the top and on the bottom of the leaves. On the surface of the leaf, you will see blister like areas that can be as large as the size of a quarter. One the other side of the leaf, you can find a gray-colored depression that matches up with the blister. As this oak tree disease progresses on the leaf, the blister turns brown, the leaf curls up and dies and it will drop prematurely. Oak tree blister does not cause tree death, but it makes the oak tree look rather unsightly.

The causes of the oak tree blister are environmental. For this disease to occur, the weather must be unseasonably mild, wet and humid in the spring. If these factors occur during the spring or your neighbor has a tree with this disease, it’s possible that yours can become infected. Why? The spores of the disease are easily transported through wind and rain.

To reduce your chances of getting this oak tree disease, you need to clean up your garden space. Remove all the fallen leaves and throw them away. If you have had the disease, do not compost your leaves. The spores will remain in the compost. 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 is first seen as a browning of the leaves and twigs that eventually die back. You can also see it present as cupping and browning along the leaf veins in slightly older leaves. Mature leaves are typically not affected by anthracnose. Another characteristic of this oak tree disease is the presence of small fruiting bodies on the underside of affected leaves. These fruiting bodies usually follow the vein of the leaf. Anthracnose is fungal in nature and survives in twigs and plant debris. The disease loves mild winters so it can remain active. Wind and rain are how it spreads from one twig or branch to another and one tree to another.

Your tree may look untidy if it’s affected with anthracnose, but it’s not a deadly oak tree disease. To avoid this problem or help a tree affected with it, you should make sure the tree is properly fed. Next, prune back the lower branches of the oak tree. This increased air circulation around the branches. This helps dry out the immediate environment around the tree. Since fungi like moist environments, by pruning you are helping to keep the environment healthy for your oak tree. Rake up the leaves and twigs that fall from your tree. Dispose of the leaves by placing them in the trash or burning them.

Tubakia Leaf Spot

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

If the winters are mild, the fungus can live in twig and leaf debris. Like all fungi, it thrives on wet, warm and humid air. Although both white oaks and red oaks can get this disease, the red oak seems to be more susceptible to tubakia leaf spots.

Don’t worry if you find tubakia leaf spots on your oak trees. You can treat them with a few simple steps. First, make sure your oak is in good health. You want to ensure that it’s receiving proper nutrition via fertilizer. You also want to give your tree enough water. It’s a good idea to improve air circulation around the tree. This is done by pruning back the lower branches. Finally, you’ll want to clean up underneath the tree and dispose of leaves and twigs in the trash. This will reduce the chances of a reinfestation of the fungus.

Powdery Mildew

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

A cool, moist spring is a wonderful environment for powdery mildew to grow in. 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 powdery mildew, you should remove any fallen leaves and/or twigs. You should water your tree in the morning only and prune away any deformed branches or leaves.

As you can see, oak tree diseases can be pretty problematic. Next week, we’ll focus on insect-caused oak tree diseases. If you have questions about the health of your oak tree, please give us a call at 512-341-8888. We’ll be happy to help you.

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