Oak Wilt Cause & Effect

Tips about Texas Trees and Lawns: AgriLife Extension Office hosts oak wilt, tree and lawn care workshop May 9 presented by Texas A&M Forest Service

CLIFTON – The Texas climate is not an easy one for plants, shrubs and trees; they have to contend with extreme dry and hot conditions as well as extreme cold snaps. And those wanting to maintain the health of their trees and lawns can always use some extra information on how to deal with these conditions.

Just days after flood waters in Clifton lapped against the Central Texas Youth Fair Home Economics building foundation after extreme heavy spring rains, interested citizens gathered for three very interesting talks by experts on Oak Wilt, general tree care and keeping a Texas lawn healthy.

Texas A&M Forest Service expert for the Hamilton region, which includes Bosque, Brown, Coleman, Comanche, Coryell, Hamilton, Hill, McLennan, and Mills, Robert Hawthorne informed those present on Oak Wilt, its cause and effect, detection, how to mitigate spread and cost sharing possibilities. Oak Wilt presented itself in Texas since the early 1960s, migrating south from the North, and wreaked havoc among the Central Texas live oaks.

Oak Wilt may reduce urban and suburban property values by 15-20 percent. The fungus that causes the vascular disease, spreads through the live oaks interconnected root systems. The rate of spread averages 75 feet per year through the root system. Sap beetles spread the spores above ground after eating from the fungal mat on Red Oaks.

“The fungus itself does not cause the tree to die,” Hawthorne said. “It is the trees reaction to the fungus, causing blockages in the vascular system that does.”

Starting with rapid defoliation within three to six months of infection the Live Oak dies. With a five – 15 percent survival rate in Live Oaks and 100 percent mortality – within four to six weeks – in Red Oaks, management before infection is therefore key. Veinal necrosis, vein banding, tip burn and marginal necrosis are all symptoms of the fungal infection.

Fighting Oak Wilt is of major importance and needs a multi-pronged approach:

Preventing new infections:
- removing and disposing of oak wilt-infected red oaks immediately
- avoid wounding oak trees, including pruning, from February through June.
- paint all wounds and fresh stumps immediately, regardless of season; also limb damage from storms
- Red oak wood that is suspected of infection should not be stored.
Diversifying the landscape:
- plant trees that are native and/or adapted to your area like Elm, Red Bud, Pecan, Texas Persimmon and Mexican Plum; avoid invasive species like Chinese Pistachio. Renee Burks from B&H Oak Wilt Services based in Hamilton also advocated for diversity in native trees and shrubs.

“I love me some trees, but some trees just don’t belong here, like palm trees and pine trees,” Burks said. “They just don’t like the cold or drought.”

favor a diversity of tree species.
Stop Spread through root connections:
- install a trench at least four feet deep and 100 feet beyond the perimeter of infection centers (last symptomatic tree) to break up root connections.
- cut or uproot all trees within the 100-foot barrier (except those injected with fungicide).
Inject high-value oaks with fungicide which has a 75-85 percent success rate:
- identify susceptible, high-value oak trees in proximity to expanding oak wilt infection centers.
- consult a trained and licensed arborist (with certified applicator’s license) for treatment of susceptible trees with macro injections of propiconazole. was present to offer information on tree care. She and her daughter Nola Hayes assist in Oak Wilt Prevention services.

These measures can be expensive, and there is a cost-sharing program in the Oak Wilt Suppression Project with the application paperwork going through Hawthorne’s office. Texasoakwilt.org is a great resource, offering background information, diagrams, illustrations, photos, and videos on how to take samples, how to prevent spread and best strategies.

Should you suspect Oak Wilt on your property, contact Hawthorne at (254) 386-3361 or robert.hawthorne@tfs.tamu.edu. He can also advise on which other trees to plant Recently Hawthorne was called in regularly by worried property owners because their Live Oak were struggling. In some cases the trees were suffering due to the past two drought summers followed by winters with harsh cold snaps. The only way to confirm Oak Wilt is by sending in a sample from multiple spots from the tree. Sample should be sent to: the Texas Plant Disease Diagnostic Lab.

Burks was the Hamilton region staff forester for 28 years before she retired and Hawthorne was appointed. She stated that a mature tree has a long past history on the site and has already lived through human interactions, drought, storms, insect and disease attacks. So, the best thing is to maintain the status quo.

“You either want a beautiful yard or you want trees,” straight-talking Burks said. “You can over water trees, minimize the root system and create a breeding ground for fungus. A thirsty tree is better than a drowned tree.”

Other advice Burks gave was: if you do water do it once a month in absence of rain; avoid sprinklers and do it slow and steady in the early morning; use rainwater if possible to avoid the salts in municipal water; avoid hitting the bark by watering away from the drip line; control weeds through mulch not plastic that suffocates the superficial roots; do not fertilize trees because it will create a larger canopy the tree cannot support; and only prune to free for mowing or clear branches off a roof.

McLennan County Master Gardner Mark Barnett went on to highlight lawn care after discussing the Texas horticulture heat map, precipitation zones, soil types and planting zones. Central Texas has gone from a zone seven to a zone eight. All these aspects factor into what type of grass to choose for your lawn. He also explained different types of grasses and their growing patterns, different types of weeds and different types of herbicides and insecticides.

“It is very limited on what [grass] does well in Central Texas conditions,” Barnett reiterated. “And if you can’t grow weeds in an area, grass won’t grow there either.” His general advice was “grow it, mow it, complain about how much work it is, and still insist on having it anyway. “Healthy grass prevents the growth of certain weeds, because certain weeds do not like competition,” Barnett explained.

Most lawn diseases are fungus based, which is why he warned against overwatering. He recommended mow consistently, and adjust the mower blade heights according to the grass’ runner type. Aerating clay soil or an older lawn will allow the nutrients and air penetrate better.

Should your lawn be struggling he advised to take soil samples to determine a possible nutrient deficiency and only treat for pests and disease after you have positively identified the problem. He advised to use targeted insecticides and herbicides and not to use general purpose products. He was also not a proponent of using the combination of weed killers with fertilizer as often advertised in the media. He explained that drought-tolerant does not mean a plant or grass is heat-resistant.

Barnett showed a lot of slides showing the effects of different agents, insects, grubs and fungi on lawn grass, which was very helpful. All in all, the workshop was very informative for both beginner and more seasoned Central Texas property owners with an interest in horticulture.