Brown Patches in St. Augustine in Katy, TX

Large Patch in St. Augustine Grass
Diseased leaf

In home owner efforts to maintain a healthy lawn in the summer of 2011 we had to irrigate a great deal during the drought.  Now temperatures have come down, humidity is increased, and daylight hour is reduced in October, we are beginning to see small yellowish patches in an otherwise healthy St. Augustine lawn.  this is referred to as Brown Patch Disease.  The scientific name is Rhizoctonia solani.  The actual name, for purposes of insecticide labeling is, Large Patch.  Brown Patch is the disease of Zoysia grass.

The symptoms, as seen on the photo upper right hand corner, are irregular yellowing colored areas in St. Augustine grass with a slight orange tint along the outer margins of the patches.  These patches can be between 1 foot to 10 feet in diameter.  You will see grass within the infested area that is green.  For true diagnosis lift an infected leaf and it will easily slide out of the plant shaft and you will see the blackish fungus, per photo in right corner.  The disease typically does not affect the roots or the stolons (runners) of the turf.  consequently if temperatures rise above 85 F, the grass recomvers rapidly.
Homeowners first go to the Big Box stores and buy a fungicide.  I disagree.  I think the proper approach should be through cultural practices.  If you use a fungicide and don’t correct the over irrigation or drainage problem the diseae will quickly reinfest.  There are few fungicides that have long resdiual or adequate curative properties.  The grass leaves that are now brown do not turn green again.
I suggest instead the following:
1.  Reduce irrigation time to my recommendation on this blog.  This will be changing regularly in the fall.
2.  Discontinue nitrogen fertilizers to only a half pound of “N” per 1000 square feet with higher last number on the bags called Potassium but don’t exceed 1 pound of “K” per 1000.
3.  Core areate.
4.  Apply compost or a compost tea that has beneficial bacteria, Streptomyces and beneficial fungi called Trichoderma.
5.  Mow the grass at 3 inches and bag it.
6.  Apply sulfur products to reduce pH of our soils.
7.  Correct drainage problems.
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