Bug Master Bulletin

Brown Patch Disease in St. Augustine Grass

Q. What is Brown Patch?
A. Brown patch is caused by the fungus Rhizoctonia solani. It can infect all grasses grown in Florida. In our area, St. Augustine grass is the most affected species. This fungus is worldwide infecting a wide range both ornamental plants and food crops.

Q. Why do I only see it during the cooler months?
A. Rhizoctonia is present year round in the soil, but is most active from October through March when night temperatures begin to fall. Higher spring and summer temperatures cause the disease to go dormant but it is still present in the soil and thatch layers.

Q. Does Brown Patch kill my grass?
A. No, the fungus kills leaf blades, not the roots.

Q. What can be done to control Brown Patch?
A. Since the pathogen (Rhizoctonia) and a host (the grass) are always present, it is environmental conditions that trigger disease development. That main trigger is temperature for which there is no control. Factors that increase disease severity are excess moisture, soluble nitrogen and stress such as shade, compaction and mowing.

Below are some tips to help reduce Brown Patch severity:
1. Reduce irrigation during the cooler months, water only as needed.
2. Raise the mowing height, use sharp blades and mow diseased areas last.
3. Only mow areas that need it, shaded or areas on the north side of house may not need to be mowed as frequently.
4. Do not apply excessive amounts of highly soluble nitrogen fertilizers, if Bug Master fertilizers your lawn, we do not use liquid fertilizers and our granular blends contain slow release Nitrogen.
5. Highly compacted turf areas can be core aerated to relieve compaction.

Q. What about fungicide treatments?
A. Applying the right fungicide can arrest the disease and decrease its severity, however following the above recommendations helps in the control. We apply the most effective fungicides available and rotate products to reduce potential resistance buildup.

Q. Why do I still see brown spots even after a treatment?
A. Fungicides do not promote the growth of turfgrass. The symptoms of the disease will not disappear until the grass has replaced those diseased leaves. Since new growth is very slow to occur during the cooler months when Brown Patch is active, the symptoms may not disappear until spring. Raking the affected areas to remove the dead leaves can improve turf appearance


Written by:
Brian Combs, General Manager, M. Ag. CPH, CCA, CPO,
Certified Professional Horticulturist - Certified Consulting Arborist
Member of the American Society of Consulting Arborist