Question
I live in Western South Carolina near Augusta Ga.   Eighteen months ago I moved into a new house on the banks of a lake.   I strip sodded much of my 1.2 acre lawn with centipede grass and installed a well with a large sprinkler system.   I am very pleased with the beautiful lawn that is developing; however, a couple of small areas (about 10 sq. ft. each) have begun to turn slightly yellow with brown grass appearing under the new grass outgrowth. What can I do to correct this problem?  

Answer
Hi Don Barnes,

Without a visible inspection of your lawn situation please realize the limitations here in providing a precise diagnosis and specifics for your situation.
Thank You for the information you have provided so far.

"...slightly yellow with brown grass..."

Be sure there have been no chemical spills causing the turf-grass appearance problem.  This time of years chlorinated swimming pool water is a major cause of turf-grass yellowing and decline.

Anything blocking the sun-light even temporarily for a few hours or days during warm weather could also cause the symptoms you mention.

Dig-up some of the sod to see if there are GRUB-WORMS feeding on the grass roots.  These can cause localized vegetation appearance problems.  Use an appropriate insecticide to eliminate a grub-worm pest in the root-zone.

Lawns can also be infected with bacteria, viruses and fungi.  Fungi are the most common pathogenic agents and these can sometimes cause the symptoms you mention.  Take a closer look at the grass foliage to see if there is any indication of a microscopic fungus affecting the leaves.  Garden centers will usually have a FUNGICIDE to treat these types of problems.  There are no treatments for bacterial or viral problems, and the lawn should be destroyed if these are diagnosed.

Otherwise, the main cause of turf-grass vegetation yellowing (a condition called 'CHLOROSIS') is due to a deficiency of ionic IRON in the top-soil.  However, this is usually more disseminated in areas rather than localized to well-defined areas.  Perhaps the top-soil is not uniformly defined in its physics and chemistry in your case, so there is localized iron-deficiency.  You safely treat the entire lawn or the affected areas with iron supplements or commercial preparations such as 'ironite'.
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ABOUT "HOT-SPOTS" in SUMMER LAWNS.

Every year, as the heat approaches, look for the "Hot-Spots" in the lawn.  These are areas that will weaken and look punk as temperatures rise above 85 degrees F. (~30 C.) or so.  Depending upon your grass type, you can often cover these problem areas with some commercial packaged soil amendments such as potting soil or compost.  The grass will eventually fill in or can be re-seeded.  With larger problem areas, you may want to truck-in commercial high quality top soil and rich-mix top-soil blends. Adding soil amendments and increasing the humus and organic matter content of the top soil will help it and the root-zone to conserve moisture during the warm, windy and dry times when moisture is either absent or rapidly lost to the air.  Schedule to have your lawn lush and well fed and the top soil optimized BEFORE the summer hot weather arrives.  Eventually, your top-soil will become more able to support a well-hydrated stand of turf during the heat.
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ABOUT WATERING:

OVER WATERING is a main cause of FUNGAL DISEASES and Mushrooms-Toadstools.

Regular "Clock-timed" watering causes a "spoiled, shallow and weak root system" unable to cope with hot weather conditions.


Unless you have a COMPUTER CONTROLLED IRRIGATION SYSTEM, i.e. one which automatically accounts for not only how much water rains are supplying to the lawn but also keeps a record of quantities applied to the lawn, DO NOT totally water your lawn with clock-timed regularity.  This can be a big mistake.

It is a common error with watering and sprinkler systems in particular to water with clock-timed regularity .  Lawns are best watered on a visually inspected and "as needed" system.  You should know how much water your sprinkler system delivers and also have a rain-gauge to help keep watering to within 1-3 inches per week.  Climate and weather factors of humidity, barometric pressure, winds, and micro-climates, soil drainage-physics etc., can make clock-timed watering more than in-efficient and un-reliable. A well hydrated stand of turf grass should bounce back when compressed by foot traffic; it should also be able to go several days between soakings in mild weather...this promotes deeper rooting and helps to get by in dry times. A single good deep soaking is better than frequent smaller waterings.

Watering at nights is usually more practical and efficient.  The idea is to NOT lose water by winds and evaporation effects which are usually less intense at night.
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Tip:
Excessive moisture in a high nitrate-fertile cool top soil can cause fungal blooms and turf-grass diseases. Do not contribute to these conditions by over-watering or over-fertilizing your lawn when the turf grass is in a low metabolic state (temperate climate fall and winter seasons) and not actively using the salts.  Never fertilize a lawn during drought conditions.
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About Fertilizing:

DO NOT FERTILIZE a lawn during drought conditions!

Commercially bagged fertilizers (all are "salts") will usually be marked with their "NPK"  MINERAL ELEMENT per-centages.  This refers to the amount of N=NITROGEN, P=PHOSPHOROUS, K= "KALIUM" (ancient name for "potassium").  All of these elements (and several others) can be used-up, depleted,i leached or chemically bound-up in the root-zone and all are needed for normal grass and plant health.  A soil, as part of a unique multi-million year ecosystem, will have its own local "mineral structure," chemistry and physics.  A soil test can be informative and may indicate the best actions to take to get the lawns and gardens we want. Garden centers will often have a basic soil-testing kit at a reasonable price.

Using compost is a great way to insure your soil is constantly improving over the years and top-dressing with compost restores harvested (by mowing) and leached minerals in lawn soils. Commercially bagged high grade compost is cheap and readily available at any garden center or department stores like Home Depot.
Compost can also sometimes be purchased by the truck-load from local suppliers.

Function of Organic Matter in Soils:
http://www.ar.wroc.pl/~weber/rola2.htm

DO NOT FERTILIZE a lawn during drought conditions!

More about Nitrate and Nitrogen:
http://muextension.missouri.edu/explore/agguides/agchem/g09804.htm

Lawn Science Soil Fertility Web-page:
http://hometown.aol.com/eilatlog/fert/fertilex.html
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A Laboratory SOIL TEST may well define your top soil's chemistry and physics and prevent future problems by diagnosing them early. A good top-soil should be sufficiently "loamy" with good tilth-drainage and fertility factors and also proper acidity (pH).  A  expense for a soil test may save you time, work and money later on.  Some garden centers sell home testing kits.  (more about test-kits below)


Lawn and Garden centers will usually sell a variety of SOIL AMENDMENTS or 'conditioners'.


IMPROVE SOIL by top dressing and/or working in  SOIL AMENDMENTS: high quality top soils and 'Rich-Mixes' (from your local trucking suppliers), compost (commercial or home made), humus-organic matter/manures/peat-moss, and sand or Kaolin/clay (if there are drainage problems). You can do this to bare lawn areas easily.  Where lawn areas continually seem to suffer from poor soil quality, partial or total renovation may be in order. Roto-tilling amendments into the existing top soil is an excellent way to prep an area for seeding grasses or laying sod. The old grass may need to be eradicated before re-seeding or "up-grading" to a more care-free hybrid.

Learn About COMPOST...aka "GARDNER'S GOLD".
Using commercial or home-made compost is a great way to insure your soil is CONSTANTLY IMPROVING over the years.
Composting and adding organic humus will help the soil become more "sponge-like" so it can hold water better and need less water applied to it. Your lawn will be better able to survive droughts/stress with regular additions of compost to the mid-summer "Hot-Spots."

COMPOSTING can return nutrients and minerals to your lawn and save you money while improving the root-zone...don't trash your grass and herbaceous debris, RECYCLE it by composting!
Website: http://hometown.aol.com/eilatlog/lawnologycopost.html
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ROTO-TILLING the above top-soil AMENDMENTS into the existing top soil will help to mix everything to a uniform consistency for a balanced soil chemistry and physics.
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Tip:
If, after working to improve the existing top soil, you can get your top soil and root zone so structured to be healthy enough to support several pounds of mail-ordered earthworms,...these will work 24/7 and multiply exponentially to  help keep your soil fertile, aerated and ecologically well balanced.
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With a good fertile-loamy well draining top-soil, best quality hybrid grass type(s), 1-3 inches of water per week, plenty of sun-light, ...almost anyone can have an excellent lawn with a minimum maintenance effort.
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I Hope this has answered your question(s)!

Visit my Lawn & Gardens webpage for more Lawn and Garden Tips, Facts and Links:
http://hometown.aol.com/eilatlog/lawnol.html

Your Questions and Comments are welcome at ALLEXPERTS.com

___ Jim Gibbs,
    Microbiologist/Botanist