Brown Patch/St. Augustine Fungus #156007 - Ask Extension


Brown Patch/St. Augustine Fungus #156007

Asked October 07, 2013, 11:31 AM EDT

I have a circular brown patch, approximately 24 inches in diameter. This is along the property line in a residential lot which is lower to accommodate drainage. I have reduced irrigation but I cannot persuade my neighbors to do the same.

What is a good fungicide to treat this area?

Fort Bend County Texas

Expert Response

Hello and thanks for submitting your questions to eXtension online.  I am the horticulturist with Texas A&M AgriLife Extension in Fort Bend County.

With fall night temperatures starting to drop, conditions for large patch (brown patch) fungus to take hold are here.  St. Augustine needs three things to happen for this fungus to flare up: cool nights, lengths of damp soil conditions, wet foliage during dark hours.  If you or your neighbor are guilty of watering at night, this is adding to the problem.  This time of year, if rainfall is average, as it is, you don't need to irrigate more than once maybe twice per week.  Watering every day, or every other day is too much, and this will keep the soil saturated, lending to more incidence and spread of disease.

Another thing with fungus is that people tend to think the condition is nutrient deficiency at first and then apply a fertilizer.  The new growth that occurs soon after is very susceptible to fungal growth. Quick release fertilizers are bad news during large patch season.  If you are applying any fall feeding, I'd go with either finished compost, a blended organic lawn fertilizer (some include beneficial fungi for disease prevention), or a light application of slow release fertilizer.

Fungicide applications are curative in nature, not preventative.  The best way to stop lawn fungal diseases is by changing your habits to lessen the conditions for development.  Curative applications will stop the active spread of the pathogen.  It won't fix the damage that has been done to your grass, and it most likely won't get rid of the fungal development or spore populations in the area.  Meaning, fungicides are a quick fix and need to be re-applied every couple weeks during the active season for disease spread.  Most garden suppliers offer a range of products: Bayer, Scotts, Ortho, Bonide, Spectricide, etc.  Products listed as "systemic" may give you a little longer control. Products with active ingredient Myclobutanil offer systemic qualities, but look on label for "systemic" control.  For active disease growth, I would recommend a liquid form, has a quicker action than granule.

Below are links to some good reading on common lawn disease and how and why they occur.  They might be good reads to pass on to your neighbor.

Best of luck and good day,


Boone Holladay Replied October 07, 2013, 2:17 PM EDT

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