Question
I am preparing to lay a new Tall Fescue sod lawn on soil that previously had alot of bermuda grass.
So far I have removed as much of the bermuda as possible and tilled the soil with a 50% mixture of compost.
Before I lay the sod, is there a product(preferably organic)that I could add to the soil to keep the bermuda from reemerging ?
Thanks,
Matt
San Diego,Ca

Answer
By selecting Tall Fescue, you have picked a Grass that is at the center of some heavy research into the subject of Weed control.

In one test in 2007 at North Carolina State Unversity, Tall Fescue mowed at a height of 4 inches ended the season with ZERO percent contamination of Bermudagrass.

ZERO!

The same Grass mowed at 1 inch suffered from a 95 percent contamination in the same trial.

Mowing is EVERYTHING when it comes to maintaining a Weed-free Tall Fescue Lawn.  The higher mowing captures Sunlight up and down the blade, soaking up rays before they reach feisty, sun-starved Bermudagrass.  This is no small feat.  Bermudagrass is one of the top most terrible things that can happen to a homeowner's Lawn.  With Tall Fescue, scientists have figured out how to stop it.  I can't tell you how pleased I was to peruse the results of that latest trial.  Hot diggity dog!

But...

the trial of which I speak was conducted in one of the USDA Zones where Tall Fescue thrives: Zone 7.

This Cool Season species is not the Grass of Choice for your Zone 10 drought-threatened region.  April's average rain in San Diego is 0.75 of an inch in a good year.

'Worst drought in 500 years' is what the San Diego Union-Tribune called it back in 2004.  Even with no instant replay on the horizon, this is still not the best of times to be growing a Grass that grows best well-watered and cucumber-cool.  Not even with the record low temps recorded this year.  The National Weather Service's Climate Prediction Center predicts continued moderate drought in Southern California and for the rest of this month, at least, 'large parts of the western US are 10 to 20 degrees F below average:

http://www.cpc.ncep.noaa.gov/

On the bright side, figure that the Compost you have unleashed is going to do some really nice things for your new Sod.  Not only will it generate a balanced diet long-term (thank you Messrs Microbes), but it will get the Sod roots off to a terrific start by (hopefully) providing ideal conditions for the Neotyphodium coenophialum Fungus/Fescue friendship that renders this turfgrass so tough.  Believe me, this is a Fungus you WANT in your Lawn if you're growing Tall Fescue.  As the USDA website puts it:

'Agricultural Research Service scientists and their university colleagues have found that the N. coenophialum Fungus seems to perform an important ecological function, helping the plant store more organic Carbon and Nitrogen in the soil.  They have also found that it helps Fescue close its leaf stomates quicker to conserve moisture in a drought, as well as improve growth efficiency.

'In return, the Fescue gives the Fungus a home and a way to get water, energy, and nutrients.  It also gives the Fungus a way to propagate itself by infecting seed so it can live in the new plants.'

Although N. coenophialum lives in Fescue stems, the Fungus still appears to direct root growth toward maximum capture of water and nutrients.  And although farmers don't like this Fungus (it sickens livestock that eats 'contaminated' Fescue), it appears to be the key to super-efficiency of Fescue roots.  The Fungus-infected roots are far superior, capturing nutrients even in the poorest Soil and grabbing H2O under extreme conditions.  Soil with high organic content supports lush growth with less stress.  It can only help your Fescue exercise the kind of muscles it needs to deliver that knockout punch to wayward Bermudagrasses.

That's state of the art as of April 2008 as I know it, at least.  Resist 'fertilizing' your newly rolled Sod after touchdown -- it's been thru enough already, and the roots have much more to reap from beneficial association with Fungal friends than from a few shots of concentrated chemical Nitrogen that people love to pour on their new Lawns.  Stress it less with long, deep waterings, appropriate waits between drinks, and intelligent Lawncare.

Hope this was not overly technical.  I could go on and on and on...

Your comments invited.  Thank you for your question,

L.I.G.