How to Treat St Augustine Grass Fungus and Revive Brown Spots

By: Ken Wilson

After battling crabgrass and chinch bugs in St Augustine grass, you may face a new adversary, a grass fungus called Rhizoctonia solani, commonly known as brown patch.

Fungicides formulated to fight off brown spot fungus in St Augustine grass will kill the fungus. Ensuring the grass dries properly, is well-aired, and receives ample sunlight will further kill the fungus and revive the brown spots. Refrain from applying fertilizers containing nitrogen.

The first signs of brown patch fungus in St Augustine grass are the appearance of off-colored patches. These patches rapidly expand outward, changing from yellow to reddish brown, brown, and straw-colored. Therefore, early detection is vital in combating St Augustine grass fungus.

How to Treat St Augustine Grass Fungus

Fortunately, several ways exist to treat St Augustine grass fungus, reducing the damage and restoring it to its former glory. The most important things to do upon discovering the fungus.

  • It is crucial to dry out the grass as much as possible. Wait to apply water until the grass has dried out. Fungus develops when the grass endures extended periods of rain, excessive irrigation, or high humidity. Drying out the grass will expedite its recovery.
  • Refrain from fertilizing the grass since fertilizers contain nitrogen. Fungus feeds on nitrogen hence fertilizing the grass will only worsen the condition.
  • Add slow-release potassium to the grass to aid restoration. Potassium stimulates root growth that, in turn, aids in recovering the grass.
  • When mowing, do not mow the brown spots. Mow around them. The fungus will be transferred to other lawn parts if you mow the brown spots and do not clean the blades afterward. If mowing the brown spots is deemed necessary, mow them last and ensure cleaning the mower blades to remove any traces of fungus.

How to Control the Moisture of St Augustine Grass

Excess moisture is the root cause of St Augustine Grass fungus. Water your lawn in the early morning, allowing nature to naturally dry out the grass via the sun's warmth.

Do not water grass in the evening since it will stay moist for too long, creating the perfect breeding ground for the fungus. Therefore, controlling the moisture of St Augustine grass is crucial to prevent fungus. Providing the moisture could be controlled, and the grass had time to dry out, the fungus will die out due to lack of moisture.

How to Treat St Augustine Grass Fungus Using Fungicide

It is impossible to control the weather. In cases of unpredicted rainfall and prolonged high humidity levels, it may be necessary to use a fungicide to kill St Augustine grass fungus.

The best way for lawn owners is to purchase a fungicide formulated to eradicate brown spot or large spot fungus. Look out for combination fungus control products that specify brown spot fungus, are easy and safe to use, and are accompanied by proper instructions. Dry granular fungicide such as Fluoxastrobin 1 is an excellent, easy-to-use product.

Follow the steps on the container, apply as directed, and your grass should start recovering in a few days.

How to Revive Brown Spots

After eradicating the St Augustine grass fungus, the brown spots will remain until the grass has had time to fully recover. It is customary to apply a layer of soil over the brown spots where the grass thinned out. Spring is the ideal time to cover patches with fresh soil since it gives the damaged areas of the grass time to grow out and be mowed away.

It is possible to revive the brown spots quicker by placing plugs or a few pieces of sod in the areas with brown spots. Once again, it is advised that this is done during spring. Prepare the areas for plugs or sods by applying a generous layer of good quality lawn soil such as Scotts Turf Builder Lawn Soil.

The sods or plugs can be laid directly on the soil, lightly press down, and water. Water the new grass daily for the first week and only as needed afterward. Given time and care, the new grass will quickly fill the thinned-out areas.

How to Prevent and Control St Augustine Grass Fungus

Beware that St Augustine grass fungus can survive the harshest of summer temperatures to reappear once the seasons change. The fungus survives the hot, dry summer conditions as spores and fungal mycelium stick to dead foliage beneath the thatch layer.

Once the moisture and humidity levels rise, the spores the fungus produced will spread in various ways. It is, therefore, essential to do everything necessary to prevent the fungus from reappearing in your lawn.

Below are seven ways to prevent and control St Augustine grass fungus:

  • Reducing the thatch layer will allow sufficient water to reach the roots swiftly.
  • Do not use post-emergent weed killers on lawns infected with fungus.
  • Only mow the grass when it is dry.
  • When mowing the grass, ensure to bag and dispose of the grass clippings if fungus is present.
  • Ensure enough air circulation as well as light levels on the grass. Shaded areas must be cleared to allow more sun and air to reach the grass. Prune back nearby shrubs and cut away overhanging tree branches to allow for better air circulation and more sunlight to dry out the grassed areas.
  • Do not use fertilizers when dealing with the fungus since the fungus feeds off the nitrogen in the fertilizer.
  • Only irrigate once a week with one inch of water. Only irrigate in the early morning for the foliage to dry during the warmer time of the day.

Will St Augustine Grass Fungus Go Away by Itself?

If left untreated, St Augustine grass fungus will return. Therefore, take care to eradicate the fungus timeously. In addition, ongoing maintenance should be in place to keep the grass healthy and fungus free.

A proper treatment plan will cure St Augustine grass fungus and revive the brown spots. However, left untreated, once the fungus reaches the crown after destroying all the leaves, it will eventually kill the plant.

Final Thoughts

St Augustine grass recovers from fungus with proper care, although it may take a few weeks to recuperate. Once the fungus is eradicated, the brown spots left by the fungus will dissipate, and new grass will sprout. (Related article: 6 Steps To Caring For St Augustine Grass So It Grows Lush)

About the author 

Ken Wilson

Long time career in the home services industry from remodeling to patio construction. Currently residing to in SWFL and active contributor to multiple home & garden publications.