Oak Wilt: What’s With Those HOA Warning Signs?

On the way out of the house, this morning, you noticed that your Live Oaks could use a bit of trimming.  Now, you’re on your way home from work.  You’re thinking of calling Happy Tree to do that trimming, since they did such a great job, last time around.  Suddenly, there it is:  A BIG sign posted by your HOA:  “Avoid Oak Wilt! Do not trim your Oaks from mid-February through mid-June!”  What is going on?  Should you forget about having your Oaks trimmed, since it’s the middle of April?

Oak wilt is caused by the fungal pathogen Ceratocystis fagacearum.  This fungus invades oaks, mainly Red Oaks and Live Oaks, via root grafting from previously infected trees, and by having fungal spores deposited in open wounds and cuts by a vector agent, the Nitidulid Beetle.  In the case of spore deposition by the beetle, once the spores germinate in the sap and conductive tissue of the tree, the fungus circulates throughout the tree.  When the growing fungal pathogen is established in the conductive tissue, the leaves of the tree can no longer transport sugars throughout the tree, and water transport is also inhibited.  This results in very rapid death, in Red Oaks, and a downward mortality spiral, in Live Oaks.  White Oaks can also get oak wilt, although there is some evidence that they have more resistance to it than the aforementioned Red and Live Oaks.

Signs of oak wilt infection are fairly clear in Live Oaks:  Veinal necrosis, a pattern seen in leaves where the veins are orange, spreading out in a diffuse orange to the surrounding green leaf tissue, is a fairly reliable confirmation of infection.  Live Oaks can survive an infection for a period of years, with more and more leaves showing the veinal necrosis symptom until the time that most leaves have fallen and are no longer replaced by the tree.  Death follows. Foliar symptoms of oak wilt on Red Oaks are less distinct. In early spring, young leaves simply wilt, turning pale green and brown, usually remaining attached for a period of time. Mature leaves develop dark green, water-soaked symptoms, or turn pale green or bronze, starting at the leaf margins and progressing inward. This can begin on one branch and quickly engulf the entire tree. Red Oaks generally die within 4-6 weeks.

Red Oaks develop fungal mats during the infective process.  These mats are composed of groups of spore-bearing bodies that grow under the bark, raising it, slightly, in areas, normally on the trunk.  The mats put off a distinctive odor, similar to Juicy Fruit gum, as I perceive it.  The nitidulid beetles can smell this odor from a good distance away, depending on prevailing wind conditions.  They land on the tree, eat the fungal mats, and pick up spores in the process.

Now, we’re getting back to the first paragraph of this article:  When you cut an oak limb, and fail to paint the cut within the first fifteen minutes, you are sending an olfactory “come and get it” to every nitidulid beetle in the area.  The beetles are attracted to the sap that exudes from fresh cuts in oak trees.  If the beetles have previously eaten from a fungal mat, as above, and they land on the fresh cut, to feed on the sap, the spores on their bodies, from the fungal mat, can become mired in the sap, and germinate there, to infect the tree with the new cut.

So, why the warning sign, from your HOA, with the time period for no trimming?  Nitidulid beetles are known to be active from the middle of February to the middle of June.  By convention, before that, it’s too cold, after that, it’s too hot.  Thing is, with the weird weather patterns we now have in Central Texas, nothing is certain, anymore, when it comes to nitidulid beetle life cycles.  They may be around before February and/or after June.  Nobody can be sure.

When your HOA warns you about not trimming oaks, what is the reality of the situation?  If you cut a tree, sap will exude from the cut.  If the cut is not painted, as above, there is a chance that nitidulid beetles will be attracted to the cut.  There is a chance that the beetles landing on the cut, to feed, will have oak wilt spores on their bodies, from previously feeding on infected Red Oaks.  There is a chance that some spores will germinate on the cut and infect your tree.

OK, so, what’s your best course of action?  Should the HOA sign dissuade you from trimming your trees during the time frame they post? The simple answer: YOU should NOT trim your trees, during that time.  The good news is that Happy Tree can trim your trees, year-round.  We paint all cuts, in all oaks, and in that way we protect your trees from nitidulid beetles feeding on the sap exuding from the cuts we make.  Since we climb up to many cuts we make at great heights, heights that you will not have access to, and we have pole painting rigs to assist us in painting cuts we can’t get right up to, Happy Tree makes sure that your trees maintain their optimal health, year-round.

It should be noted that root grafting is a major cause of oak wilt spread in neighboring trees.  If a tree in your area has been identified as having oak wilt, and you have oaks that are within 100’-150’ of that tree, it is a good idea to have your healthy oaks injected with the chemical propiconazole that will help protect them from the disease.  At Happy Tree, we have a Texas Licensed Pesticide Applicator who can do this job.

Should you have any questions about oak wilt, please contact us at Happy Tree.  Our Certified Arborist, Miles J. Lefler, is also a Certified Oak Wilt Specialist, ISA.  He will be happy to answer your questions.

At Happy Tree, we want to make sure that your trees stay happy and healthy.  Give us a call at: 512-212-0010.  Thanks!


By Miles J. Lefler

Certified Arborist at Happy Tree Services

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