Question
I live in Phoenix, AZ and about a year ago I put in Bermuda sod in my backyard. Slowly a portion of the area began to yellow and then die. I have tried treating it with lime and the dead spot got gigger and bigger. Then I tried mulching it. I reseeded it with Bermuda seed, I tried watering at differnt times. I tried reseeding it and remulching heavily but it has never came back. I am baffeled as part of the lawn is fine and this area just will not grow. I am unsure if I should re sod or could there be a fungal problem?

Answer
The patchy, uncooperative Grass you described is a classic symptom of There-Used-To-Be-A-Tree-Here Disease.

Homeowners LOVE to plant Trees smack in the middle of the Lawn, right behind the house.  Back decades ago, there was that very popular poem, 'I think that there will never be, a poem as lovely as a Tree,' so when people finally managed to buy a house, one of the first things they did was plant a Tree there.  It was in the planning stages for YEARS.

So, the Tree grows.... and grows.... until there is only a massive Tree back there.  And eventually it may have been damaged, and then got sick and died, or it outgrew the location.  And someone 'removed' it...  Almost!

Unfortunately, if you don't remove a tree PERFECTLY, you live with the results for the REST OF YOUR LIFE.

That goes for any Tree.  Maple, oak, spruce, pine, sycamore.  ANY Tree.

Deep removal of the entire trunk is the ONLY way to stop the trunk from rotting for the next 100 years under your lawn.  Fungi in charge of decomposing it suck all Nitrogen from the Soil, leaving NOTHING for the Grass upstairs.  It causes wide, ugly, dead patches where the Tree used to be.

Sure, they may even have ground down the stump.  Not good enough.  Anything left must still rot -- SLOWLY -- consuming Nitrogen molecules by the ton.

Ever hear of White-Rot Fungi?

Here's a cheat sheet you will find of interest:

www.hawaii.edu/abrp/Technologies/fungus.html

Trees are wood.  Wood is Lignin.  It takes YEARS for Lignin to decompose.

Underground, it takes MORE YEARS.

The Joint Genome Institute points out that White-Rot Fungi -- so named because they turn tough Brown Lignin into soft White Cellulose -- 'are the only microbes capable of efficient depolymerization and mineralization of Lignin':

genome.jgi-psf.org/whiterot1/whiterot1.home.html

Get to know and LOVE your White-Rot Fungi.  They and they alone are in charge of making your invisible Tree stump vanish and your Grass grow Green again.

Some quick notes on Fungi: They are ALL aerobic.  They ALL need moisture to work.  Wood decays fastest at higher temperatures; below 50 degrees F, decay slows considerably as the Fungi metabolism drops, and at lower temps, all Fungi go dormant and their work comes to a halt.  If you roll out a Green Lawn over that site, the Grass in the area will progressively vanish.  You can replace it again and again, but this unfortunately is going to happen until there is NO MORE STUMP left there.

The only way to solve this problem is to remove every last piece of ground and un-ground stump from the Soil OR grow something else there.

Cornell University scientists at the School of Engineering have studied ways to speed up the way Fungi break down the Lignin in wood.  The school published their findings, 'The Effect of Lignin on Biodegradability', and posted them online:

compost.css.cornell.edu/calc/lignin.html

They state: 'Adding small quantities of Nitrogen to woody materials can increase Lignin degradation rates.'

Other authorities point out the Sugar is the perfect White-Rot Fungus food; 'feeding' those areas will help to accelerate the breakdown of Wood.

If you're thinking you can solve this with a covering of more topsoil over those areas, understand that submerging the area under more Soil will slow down decomposition (your great grandchildren may still be dealing with this problem) by severely limiting the Oxygen available to those aerobic Fungi.

I think that I will never see,
Turfgrass tough as White Rot Fungi,
If you don't get the whole tree stump,
you'll deal forever with that bump,
Nitrogen may do some good
to melt the Lignin in the wood.
But if you want Grass in the same place,
you'll have to get every last trace.

Good luck.

Thanks for writing.

THE LONG ISLAND GARDENER