Yellow, brown mottled live oak trees

[MReed53]

We have a live oak in our front yard in San Antonio that was planted by the developer. Most of our neighbors' oaks of similar size and age (approx. 12' high, 5-years since planting) have dark green leaves, but our tree's leaves are yellowish and brown-mottled. I took a sample to a nursery fearing it was oak wilt, and was told it appeared to be "environmental," but got no additional information. I also tried emailing our area extension agent with photos and got no reply. I thought perhaps it was an iron deficiency and scattered some fertilizer with iron, but I am groping in the dark. Here are some photos of the tree and its leaves. I don't see why it should be environmental when trees growing in the same soil on our block as well as wild trees in the green belt behind us appear to be fine. Any help would be greatly appreciated.

 

[treeseer]

if you pull away mulch and dirt and take a pic of the base and topmost roots that may help find the problem.

 

[MReed53]

I'll take a look

I'll see if I can pull away some of the St. Augustine turf and expose any roots. There is no mulch piled around the tree, though. Some of the people around here did pile up mulch high onto the trunk, but we made a point to avoid that. I have chinquapin oak I planted on the other side of the yard about three years ago and it's been going great guns from day one.