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Friday - September 05, 2008

From: Plano, TX
Region: Southwest
Topic: Trees
Title: Bur oak defoliation
Answered by: Joe Marcus

QUESTION:

I have a bur oak that was planted in 1993. In 2000, I had mortared stone edging (approx 5 inches deep) installed around the trunk from 4 to 6 feet away. In the last 3 years, the tree seems to be declining (early defoliation, almost dead leaves on one side at the top, khaki-colored foliage in July). I am willing to remove the edging if it will help. My questions are these: 1) Do you think the edging is the problem? 2)If it is removed, will the tree roots grow out or have I created a bowl where the roots will continue to grow circularly?

ANSWER:

The mortared edging you installed eight years has almost certainly had no part in creating on the condtion you've described. However, we are not sure just what is causing the problem. Well-established bur oaks rarely suffer from diseases, those they are notably susceptible to cotton root rot (Phymatotrichum omnivorum) and Strumella canker (Strumella corymeoidea). Cotton root rot is a particulary common problem in your area in North Texas. The most common and troublesome oak disease in Texas, Oak Wilt, does not often affect bur oaks, though it can and does occasionally. Finally, various insects and mites can attack bur oak foliage, disfiguring and even killing the affected leaves.

Environmental changes in the root zone can cause tree defoliation and decline. If you have made any major changes to the soil within the root zone of the tree - especially changes in watering, herbicide applications, any trenching, or any changes in soil depth in the last couple of years, those changes could be the cause.