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Wednesday - August 20, 2008

From: Frisco, TX
Region: Southwest
Topic: Diseases and Disorders, Planting, Soils, Trees
Title: Damage to native elm in Texas
Answered by: Barbara Medford

QUESTION:

We had a major landscape renovation done over the winter. One of the trees, an elm about 10 yrs old, remained in the bed although plants around it were removed. The tree has suddenly started turning yellow and dropping leaves in the last week. I had removed some of the over mulching around the trunk, but only about 3 inches. The oaks surrounding it appear fine. Bed drainage is good - if anything, it wasn't getting enough water. I've since watered it. The tree was fertilized last fall with "spikes" and then again in the spring.

ANSWER:

Although there are worse things that can happen to an elm, this sounds more like damage done during the landscaping. Ulmus alata (winged elm), Ulmus americana (American elm) and Ulmus crassifolia (cedar elm) all are likely candidates to be the elm in your garden, found as natives in your part of the state.

However, to start with the "worse things", these elms are all susceptible to Dutch Elm Disease, which has decimated elm populations in many parts of the United States. This Oklahoma State Cooperative Extension site on Dutch Elm Disease lists symptoms and treatments. Let's hope that is not what is wrong with your tree, because treatment pretty much involves removing the tree before any others around it are infected. Some trees are susceptible to powdery mildew, causing varying degrees of leaf color changes in Fall, right before leaves drop. Mites can yellow the foliage but usually cause no permanent damage. Scale insects can infest elms along branches.

Roots of trees are mostly in the upper 6 to 12 inches of the soil. Roots are typically found growing one to three times the height of the tree and may be smothered by adding soil or increasing the grade. It only takes a few inches of added soil to kill a sensitive mature tree. In the process of removing other plantings, your tree may have been exposed to higher levels of sunlight, particularly during this very hot summer in Texas. Your tree could have been stressed by one or more of these situations and could therefore be more prone to disease and pest infestation.

Irrigation and drainage: Improper drainage needs to be repaired. A long soak over the entire root system is preferred. Make sure surface water drains away from the tree. Apply a 2 to 4 inch layer of organic mulch such as compost, shredded bark or pine needles over the root system as far as is practical-not deeper than 4" and not piled against the trunk. Don't fertilize until the tree recovers. This website from the USDA Forest Service on Ulmus alata (winged elm) gives a pretty good summary of the various pests and diseases of the different species of the genus Ulmus. If you still are unable to determine the problem with your elm, contact the Texas A&M AgriLIFE Extension office for Collin County.