Brown Patch Fungus Active in St. Augustine Grass Lawns

Brown Patch Fungus Active in St. Augustine Grass Lawns

Brown Patch Fungus Active in St. Augustine Grass Lawns

The day/night temperatures the past few weeks (early November) have favored development of the turfgrass fungal disease called “Brown Patch”. This disease of lawns is caused by a fungal pathogen, which has the scientific name of Rhizoctonia solani. Turfgrass affected by brown patch generally will exhibit circular or irregular patches of light brown, thinned grass. Under conditions that favor this disease, these patches can coalesce increasing the size of the affected area. Understanding this disease, which is all too common in the fall on St. Augustine grass, includes the following.

How it looks (symptoms) and conditions that encourage development.

  •  Patches form up to several yards in diameter commonly develop in the fall, winter and spring when lawns are approaching (fall) or emerging (spring) from winter dormancy.
  •  Evening temperatures are typically below 68 degrees, rainfall usually increases, the lawn is over-watered and/or heavy morning dew formation is common.
  •  Active infections are noticeable by yellow leaves at the edges of patches.
  •  Leaf sheaths become rotted, and a gentle tug on the leaf blade easily separates the leaf from the runner (stolon). This can be used for early detection of this disease, before patches become severe, allowing time to treat before there is much damage.
  •  Brown patch usually does not discolor roots, as would Take-All Patch. Take-All Patch (a different disease) is more of a problem late spring to summer, with different symptoms.
  •  Brown Patch fungus develops most rapidly when air temperatures are between 75 and 85 o F and moist/wet conditions are present.
  •  Brown Patch activity generally subsides when air temperatures rise above 90 degrees F or with chilling late fall and winter-like temperature.

What can be done to minimize Brown Patch?

  •  Water infrequently, only as necessary to prevent wilt. Water early in the day to remove dew and allow the grass to dry quickly.
  •  Avoid over fertilization in spring and fall.
  •  Improve the lawn health and correct poorly drained areas to reduce damage caused by brown patch.
  •  Fungicides to control Brown Patch are available to the home consumer at most garden centers. These products are most effective when used on a preventive basis (when the disease might be expected based on grass type and weather condition). Multiple applications may be necessary. Always follow pesticide label directions.

What to expect this fall, winter and next spring?

  •  St. Augustine grass lawns typically recover from this disease; however, Brown Patch activity has occurred late this year due to high temperatures and dry conditions extending into early fall.
  •  If fungicides are applied effectively now, it can protect the unaffected lawn areas and stop the fungal activity in the diseased areas.
  •  There is very little growing season left for St. Augustine grass to make a full recovery this fall as chilling temperatures will slow its growth before it goes dormant at the first frost.
  •  With the onset of chilling temperatures the fungus activity will decline.
  •  For improved lawn quality, be prepared to treat the areas with a fungicide next spring if the patches are slow to green-up or the weather conditions favor prolonged disease activity. Encourage spring re- growth with appropriate application of fertilizer.

David Chalmers, State Extension Turfgrass Specialist, 
Texas Cooperative Extension

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