Tree Diseases to Watch for in Dallas

Hypoxylon canker on a tree

We love our trees for the beauty they add to the landscape and the value they add to the property. Sometimes it’s easy to take a big hardy tree for granted while we tend to lawn and garden, but even the sturdiest tree can fall victim to disease. If you want to keep your lofty shade-bearers, you need to show them a little love. Janet Laminack, a Texas A&M AgriLife Extension Horticulture Agent, keeps an eye on tree diseases in the Dallas Metroplex area. Here are some of the worst tree diseases to watch out for in Dallas.

Hypoxylon Canker

This disease (pictured above) with the peculiar name makes the top of the list for two reasons: It can kill trees in Dallas quickly, and there’s no cure for it. “It’s widespread. It attacks trees that are already in decline,” Laminack said. Hypoxylon canker occurs most often during a drought – and Dallas is no stranger to droughts. It strikes oaks primarily, but can also infect sycamore, elm, and pecan, all popular in the region. Stress can make it worse. “Recently we’ve had drought and then flooding, which is very stressful to trees,” Laminack said. Telltale signs of the disease are bark peeling off the trunk and branches, the appearance of dark spores, and loss of leaves beginning on the upper branches.

What you can do about it

Because there’s no cure, preventive maintenance is your best bet. Make sure your trees get adequate water during droughts or dry spells. Also, see that your tree gets proper “wound care” if it has broken branches, cuts, or scrapes. Don’t apply tree paint/sealer, though — that’s an outdated practice. Research shows it does harm to trees.

Fire Blight


Fire bight
These wilted leaves come to you via fire blight. Credit: Ken Johnson, Oregon State University Extension, CC by SA 2.0

This is not actually caused by fire, but rather by bacteria. It gets its name because the leaves of infected trees appear scorched. Other symptoms include cankers on branches that ooze a sticky substance. The disease most often attacks fruit trees such as apple and pear and can spread to other trees by birds and bees. If you planted a Bradford pear, one of the worst trees in Dallas, you may consider fire blight a blessing. But for everyone else, it’s a disease that can spread rapidly and incurably. It’s not necessarily fatal to the tree, if it’s spotted and treated.

What you can do about it

Prune away infected limbs, ideally in the winter. Treating your tree with fungicides before the buds open can reduce bacteria. Get rid of leaves that have dropped.

Oak Wilt

Oak wilt
The effect of oak wilt on leaves. Credit: Shutterstock.

As the name implies, this disease strikes oaks. “It’s a bad one. It’s very devastating on red oak and live oak. It clogs up their vascular systems,” Laminack said. Signs of oak wilt are leaves turning brown and then dropping off. If you don’t treat it, it can kill your tree. The disease has devastated portions of the heavily wooded Texas Hill Country. It’s spread from tree to tree through roots, spores, and by insects.

What you can do about it

Systemic fungicides are effective against oak wilt. You can also prune infected branches between December 1st and February 1st, or between July 1st and October 1st when beetles are not feeding on the sap. Cover the pruning wounds with tree paint. You should also dig a deep trench between the infected tree and other nearby oaks.

Dutch Elm Disease


Dutch elm disease
Evidence of Dutch elm disease Credit: Joseph OBrien, USDA Forest Service. CC by SA 3.0

This disease has popped up only sporadically in North Texas but makes the list because when it gets a foothold, it’s devastating. It has wiped out most of the native elm population in the Northeast and Midwest. Recently cases have been reported in Flower Mound, Southlake, and North Richland Hills. The popular Cedar Elm is susceptible to it. The disease spreads by several species of bark beetles. Symptoms include withering and yellowing of leaves starting at the top and working downward. Ultimately, roots become infected, and the tree dies.

What you can do about it

The commercial products Arbotect and Alamo have shown some effect. But by the time most people notice the disease, it’s usually too late for treatment, and the tree must be removed.

Prevention is Key

Janet Laminack
Janet Laminack

Laminack, the Denton County extension agent and a Texas A&M graduate with a master’s degree in agricultural education, says the best way to protect your trees from disease is prevention.

She advises to keep an eye out for signs of disease, such as wilting or loss of leaves and shedding bark. Tree “wounds” also invite disease, and she warns against unnecessary pruning because cut limbs invite pests that carry disease. “People over-prune – I don’t know why. Maybe because it makes it easier to mow under trees.”

She also emphasizes the need to mulch around trees. Mulch moderates soil temperature, retains moisture and “keeps trees from getting nicked by the weed-eater.” Proper watering is also vital, especially for new young trees. “Water deeply, but infrequently,” Laminack said. “New trees will need supplemental watering for at least the first three years.” She recommends buying smaller trees when you add new ones to your yard. They’ll become more resistant to disease as they grow.

Lynn Walker

Lynn Walker

Lynn Walker has been writing for radio, TV and newspapers for more than 50 years, and has expertise in news, features, humor, history, weather, genealogy, science, archaeology and government.