An Extended Guide to Tree Diseases

We cherish our trees here in North Texas. They surround us with natural beauty and protect us from the summer sun. When properly cared for, trees can also increase property value. However, like all living things, trees can succumb to diseases that affect their attractive appearance and may even lead to death.

Although our trees here in Texas require the same maintenance as other trees around the world, they are more susceptible to certain tree diseases than in other areas.

Having a basic knowledge of these tree diseases can help you become aware and treat them promptly. Unfortunately, many of these diseases are incurable, so once they have taken hold, the tree will need to be removed. Still, even in these instances, disease prevention and management are attainable goals.

To make you better aware of which tree diseases you need to look out for, we will take you through each disease one by one. In the descriptions, we will cover which trees are most susceptible to the disease, what symptoms to look for, and how the disease can be treated or prevented.

Hypoxylon Canker

Hypoxylon canker disease is common during periods of drought. It typically attacks trees that are already weakened by environmental conditions.

  • Trees most susceptible: Many native trees are vulnerable to hypoxylon canker. You will especially want to keep an eye on oaks, pecans, sycamores, and elms.
  • What to look for: Branch dieback, also known as the stag-head condition. This condition is where the uppermost branches of the tree look like a stag’s antlers. The branches are usually leafless and dead. You may also notice sapwood decay, bark peeling off of the limbs and trunk, and dark-colored spores visible on where the bark has peeled off.
  • Treatment: Hypoxylon canker disease cannot be cured. The condition is fatal and may end up killing the tree quite rapidly. At that point, the only option is to call a service to remove and dispose of the tree. Prevention is the key. Protect your trees with ample water and tending of any wounds during the drought season.

Oak Wilt

Nitidulid beetles and root grafts can spread Oak Wilt disease to other trees, so timely diagnosis is vital to keep the infection from spreading.

  • Most susceptible trees: The name says it all. Oak wilt affects oak trees. Some oaks like White, Chinquapin, Mexican, and Bur oaks are more resistant than others.
  • What to look for: Keep an eye out for browning of leaves and dropping of leaves.
  • Treatment: No known chemical treatment is capable of curing the disease, but fungicide research is continuing. Oak wilt must bemanaged through an integrated approach so that it does not spread.

Fire Blight

Fire Blight is caused by bacteria, and it spreads quickly. Cankers that develop on the tree protect the bacteria during winter. In the spring, the bacteria ooze out and spreads to other parts of the tree and trees nearby.

  • Trees most susceptible: It usually affects fruit trees. Apple and pear trees are specifically vulnerable.
  • What to look for: Foliage and blooms that blacken at a rapid pace. Shoot tips bend into a hook-like shape. Occasionally cankers develop on blackened branches
  • Treatment: When trees go dormant in winter, use sanitation pruning to remove infected wood by cutting an infected branch 4 to 6 inches below the visible injury or canker. It is crucial to avoid spreading bacteria during pruning by using a 10% bleach solution to sanitize the pruning tool before each cut.

Bacterial Leaf Scorch (BLS)

Insects like leafhoppers spread BLS bacteria. When a tree develops bacterial leaf scorch, the flow of water between its roots and leaves chokes. BLS not only harms the affected tree, but it makes the weakened tree highly susceptible to other infections or pests.

  • Trees most susceptible: Elms, oaks, box elders, and sycamores are all vulnerable to BLS.
  • What to look for: A yellow band between green tissue and the scorched tip of the leaves, defoliation of the leaves, branch dieback are all symptoms.
  • Treatment: There is no cure for BLS, but the disease can be managed, and the tree stabilized. For more information on how to create a management plan, visit this TNLA article


Anthracnose is a fungus that develops on lower branches, following a cool, wet spring.

  • Trees most susceptible: It commonly develops on ash trees.
  • What to look for: Lesions appear on leaves.
  • Treatment: Anthracnose disease does not directly kill trees, but repeated infections can weaken trees, making them vulnerable to other problems. Prune out dead wood and destroy infected leaves. Using a copper-based fungicide can be helpful, but you must be careful. Copper can accumulate to toxic levels in the soil and kill valuable earthworms and microbes.

Mushroom Root Rot (or Oak Root Rot)

This parasitic fungi infects the roots of trees and eventually causes death, wood decay, and growth reduction. These fungi infect and kill trees that have been weakened by competition, other pests, or environmental factors. The fungi also infect healthy trees, either killing them or predisposing them to attacks by other fungi or insects.

  • Trees most susceptible: A wide range of trees like oaks and hickories, as well as many hardwoods and conifers, are susceptible to root rot.
  • What to look for: Mushrooms at the base of the tree, white fungus under the bark, symptoms may not show up for months or even years.
  • Treatment: There is no effective preventive or curative fungicide treatment for mushroom root rot. Once the tree dies, remove it and any adjacent trees that may be infected. Remove stumps root pieces from the soil. Make sure to clean all soil off of your equipment. Consider replanting only species that are not susceptible to root rot.

Powdery Mildew

Powdery mildew comes from millions of tiny fungal spores that are spread on the air currents. Symptoms usually appear late in the growing season. The fungus is most prevalent during periods of high relative humidity, in crowded conditions that prevent air circulation, or in the shade.

  • Trees most susceptible: Mildew affects all kinds of trees. It is common on cedar elm in the fall.
  • What to look for: A powdery appearance on leaves.
  • Treatment: Although common, mildew does not significantly affect the health of the tree and generally does not require management. However, to prevent the spread of mildew, do not compost any infected plants. Fungicides that effectively treat powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate.

Dutch Elm Disease

Dutch elm disease is a fungal disease spread by the elm bark beetle.

  • Trees most susceptible: As the name suggests, elm trees are vulnerable to Dutch elm disease.
  • What to look for: Wilted, yellow branches and curved twig terminals resembling a shepherd’s crook are signs of Dutch Elm disease. When cut crossways, twigs show discoloration or browning of water-conducting tissues in the sapwood.
  • Treatment: Infected trees may die in a single season or live for several years. Affected trees must be treated proactively before the disease is present. Treatment on diseased trees may not be effective because the disease progresses so quickly. A trunk injection of Propizol Fungicide is recommended as a proactive treatment or at the earliest stages of infection.

Oak Leaf Blister

Oakleaf blister is a fungus common in cool, moist conditions. It is usually seen as leaves are forming in spring.

  • Trees most susceptible: Oak trees are vulnerable to oak leaf blister.
  • What to look for: Blisters, bulges, depressions, cupping, and twisting on leaves is common. Defoliation is also common.
  • Treatment: The disease does not seriously affect the health of the tree, but the tree’s aesthetic value will be diminished. Apply a single application of a fungicide in the spring when buds are swelling to prevent oak leaf blister. Use a power sprayer to coat buds and twigs thoroughly. Chlorothalonil (Daconil) and mancozeb are fungicides that are registered for use in controlling oak leaf blister.

Cotton Root Rot

Cotton root rot is caused by a soilborne fungus that lays dormant in the soil for many years. Although this fungus has had a reputation for destroying entire cotton crops, it also affects trees.

  • Trees most susceptible: Apples, pecans, and ornamentals are most vulnerable.
  • What to look for: Leaves will yellow or bronze of leaves, wilt, and die quickly. Leaves remain firmly attached to the tree.
  • Treatment: Remove the affected tree. Because the fungus can survive in the soil for many years, you should only choose tolerant or resistant species as replacements.

And the list of tree diseases goes on and on…

As you can see, it isn’t easy to keep up with or detect all the tree diseases that could affect the trees you love. It’s also challenging to determine and implement the best management and prevention techniques for the most infectious diseases. That’s why we’re here! Our certified arborists know exactly what to look for and how to care for your backyard beauties.

If you have any concerns or questions about your trees, call us for a consultation –we’ll be happy to help!

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