Plant Answers  >  Oak Tree With Symptoms of Environmental Effects of Construction and Drought

Oak Tree With Symptoms of Environmental Effects of Construction and Drought

QUESTION:
Could you help me determine what might be causing this leaf pattern in oak trees. The trees are located on a ranch south of Menard.

Live oak wilt is in the county, but so far has not been seen in this area plus, looking at the patterns on the leaves, I don’t think this is Live oak wilt unless it is the very early stages. Two years ago they remodeled their house and this tree stands in their front yard. There was a lot of activity with trash piles in the yard near the house which has since been cleaned up. There was some root damage from putting in the carport drive next to tree from two years ago. Plus, the tree was stressed from last year extreme drought. Did not see any bark damage or insect bores, etc. Symptoms are now appearing on another tree the other side of the carport.

ANSWER:
The leaf pattern is not typical for oak wilt, so you can cross that off your list of possibilities. Oak wilt would show yellowing along the veins, progressing to brown, but not yellowing between green tissue at the veins.

Construction negative effects on trees often takes 2 to 5 years to be expressed. From your summary of recent work around this and other trees, loss of roots and drought stress are consistent with the leaf symptoms. One photo shows that major lower limbs were removed (or stubs removed) recently, and the large unhealed pruning wounds tend to weaken a tree (increase moisture loss initially, allow heart rot fungi an entry point). Grade changes, digging for utilities and foundations/slabs, and impervious paving destroy roots, and there seems to be more symptoms in proximity to the recently constructed carport.

The good news is that live oak probably has more abilities to re-grow root systems than most other native trees.

Suggestions:

Place a high priority on irrigating trees with leaf dieback symptoms--at the drip line or where construction probably damaged roots; you may be able to re-grow some of the root system even this summer.

If you are able to irrigate aggressively, there is still time for at least 1 application of a low rate of Nitrogen fertilizer to help the tree build up stored reserves in wood and roots before the winter.

Remove any nearby competitive vegetation such as mesquite, native juniper, and other native brush that has lower priority than live oak.

Apply mulch (4-6", renewed yearly at least until tree recovers) within the drip line of the most endangered trees. Spread without use of heavy equipment if possible (wheel barrel is okay), to avoid damage to root flares and roots at/near the soil surface. Almost any locally available low cost organic material is suitable (leaves, hay, wood chips from utility company right-of-way maintenance, cedar shavings, etc.) as long as it doesn't have high salt or nitrogen content or seeds of invasive plant species.

Eliminate/minimize foot/animal/equipment traffic within the drip line or wider area, to avoid further root damage from compaction, etc.

Do not use weed-and-feed lawn fertilizers (with herbicide) because tree roots can absorb enough to further weaken the tree.

In the future, avoid disturbing tree roots as much as possible. Live oak roots often extend 2.0 to 2.5 times the distance from the trunk as the tree is tall. Consider permeable paving materials to allow oxygen exchange and penetration of rainfall/irrigation.

Mark C. Black, Professor and Extension Plant Pathologist

 


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