How to Treat St Augustine Grass Fungus and Get Rid of Brown Patches

Joseph Gilpin
By Joseph Gilpin • Last Updated: June 24, 2022
Signs of fungus in st augustine grass

Brown patch fungus is a common problem on grass like Bermuda grass and St. Augustine grass. It’s caused by soil compaction, humid weather, and lack of direct sunlight in shaded areas.

St. Augustine grass, a warm-season grass that grows well in humid conditions, copes poorly against brown patch fungus. Although it has resistance to fungal diseases, it’s still prone to lawn fungus.

The most effective way of naturally treating St Augustine fungus is to cut out irregular patches in your lawn grasses before it spreads. It is best to apply chemical fungicides with azoxystrobin, flutolanil, Consan 20 or thiophanate-methyl as the active ingredient if that isn’t enough.

Grass fungus leaves large brown patches on your grass blades, rust-like growth, and the lawn fungi eventually kill any bit of lawn it touches.

It doesn’t matter whether your lawn is afflicted by Rhizoctonia or Pythium blight fungal growth. You can still treat fungus or prevent brown patches from spreading.

Let’s go over some of the common methods of preventing brown patches and treating them. These include fungicides, core aeration, and other DIY methods.

Signs of St Augustine Fungus

We must first know how to spot brown patch disease on St. Augustine Grass lawns. While there are other possible causes of browning and dead grass, here are the most common signs of fungal infections on St. Augustine lawns:

  • Stolons (horizontal stems connecting plant growth) turn yellow and later brown.
  • Brown spots on your St. Augustine lawn
  • Random yellow leaf spots appear on grass blades.
  • Dark brown fungi coat the stolons and dead grass.

St. Augustine turf can go from a beautiful lawn to a lawn overwhelmed by dead spots because of fungal diseases. These manifest as circular patches of irregular brown spots a few inches to several feet.

Aside from this, fairy ring disease causes dead patches to surround patches of vibrant green blades. Fairy fungus encircles healthy lawns and can overwhelm them if left unattended.

Fungal diseases can also affect St. Augustine grass by attacking leaf blades. They cause dark brown coloring along the edges and hard-to-control gray leaf spot resembling burnt cigarettes.

When your lawn shows signs of Augustine grass fungus, but you are unsure of what caused it (grub infestations and pet urine also eat at grass), it is best to call a lawn-care professional to confirm.

You can also call your county extension offices for laboratory contact information. You can send a sample of grass clippings and soil conditions to the labs to see which fungal disease is afflicting your lawn.

St. Augustine Grass Fungus - How to Treat and Get Rid of It

Causes of Brown Patch Disease

Brown patch disease is more likely to devour your St. Augustine lawn under high humidity and extreme rains that cause stagnant or standing water.

This is why Coastal regions like California and Florida are more prone to lawn fungus on their St. Augustine grass. It most commonly grows in the early spring.

The most common causes of brown patch disease in St. Augustine lawns are:

  • Prolonged periods of rain and muddy water in the shade
  • Overfertilizing and overwatering.
  • Too much shade. Not enough sunlight.
  • Compacted soil, not enough circulation

Cool nights and early morning temperatures between 70-90 degrees Fahrenheit are the perfect conditions for gray mold, leaf spots, and lawn fungus in St Augustine grass.

Aside from cold, damp weather, poor lawn care also contributes to brown patches spreading across your grass. Lawns that are neglected with clay soils constantly trampled on are most likely to get infected.

St. Augustine Grass Fungus

How to Treat St. Augustine Grass Fungus

Now that you know how to spot fungus and what causes it, we can go to steps on how to treat it.

St Augustine fungus treatment will depend on what type of fungus you’re dealing with. First, you will need to identify which fungus affects your lawn, whether it’s downy mildew or gray leaf spot.

Once you know the fungus affecting your lawn, you can solve your fungi problem.

Here are some of the best ways of saving your St Augustine grass from lawn fungus:

1. Replace Affected Grass With New Grass Blades

Fairy fungi form a ring of lifeless grass around green patches. Replacing this area of the lawn is the most effective against this.

Removing the sections of white soil on the outer parts of the fairy ring fungus allows you to get rid of the infectious area. Once it’s clear, you can refill the excavations with a new layer of St. Augustine grass sods.

Fairy Ring Fungi

2. Apply Azoxystrobin to Kill Fairy Ring Fungi

Another great alternative to eliminate this type of lawn fungus is Consan 20, an indoor and outdoor fungicide and disinfectant.

Fairy ring fungi also manifest as circular patches of mushrooms and overgrown or dead leaves. To save your lawn, you will need to spray anti-ring fungicides such as azoxystrobin and flutolanil.

A great fungicide alternative for this type of lawn fungus is Monterey Consan 20, an indoor and outdoor disinfectant and anti grass fungi treatment.

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Monterey LG 3240 Consan 20 Concentrate Weed Killer
  • DISEASE CONTROL - Consan 20 controls many plant diseases like anthracnose, downy mildew, leaf spot, rust, crown rot, gray mold, black spots, algae, and wilt.
  • FOLIAGE & LAWN PROTECTOR is designed for ornamental plants, grasses, trees, roses, crepe myrtles, cactus, and orchids.
  • MULTI-PURPOSE DISINFECTANT - Monterey Consan 20 can be used to disinfect hard surfaces like walls, garbage cans, cutting tools, flower buckets, walkways and fountains.

3. Treat Grey Leaf Spot Fungus Using Thiophanate-Methyl 

Grey Leaf Spot is another fungal disease. It’s distinct for its splotchy, bleached-out patches on your turfgrass. Over-fertilization and humid weather cause it. You can treat it with high-quality fungicides. In this case, thiophanate-methyl and azoxystrobin work best.

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Southern Ag - Thiomyl - Ornamental Systemic Fungicide
  • Thiomyl Systemic Fungicide, Treats Bulbs After Digging For Over-Wintering
  • Controls many stem, root & crown rots and spots

4. Alternate Anti-fungal Products

Pythium blight, also known as grease spot fungus, is another type of infection. This time, it creates greasy and sticky leaf blades on your lawn.

This fungus is notorious for growing resistant to fungicide after a while, so you must use various anti-fungal brands. One of the most effective of these treatments is Southern AG Fungicide.

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Southern Ag Garden Friendly Biological Fungicide
  • Controls plant diseases in gardens, vegetables, ornamental and fruit trees, lawns, bedding plants
  • Controls Anthracnose, brown patch, dollar spot, powdery mildew, rust, and pythium on your lawn


Prevention is always better than cure. This applies to fungus in St Augustine turf as well. Although it is treatable, it is much better to keep the disease away from your lawn than wait for it to spread.

Prevention entails creating conditions that prevent infections from developing. It would be best if you deprived them of conditions to grow in. Here are some steps to stop the dreaded fungi from dead in its tracks.

Reduce Soil Compaction

Lawn soil is prone to fungi when too compact, as nutrients don’t absorb properly. You can reduce infection by using a plug aerator. Aeration de-compacts your soil and allows plants to grow healthy.

Boost The Soil’s Nitrogen Levels

Nitrogen makes lawn soil more resistant to fungal infections. Boosting soil nitrogen is possible by leaving shaved grass when mowing. The other way of boosting nitrogen is to use nitrogen-rich fertilizers.

One of the best nitrogen fertilizers is the Simple Lawn Solutions Maximum Green and Growth.

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Maximum Green & Growth- High Nitrogen 28-0-0 NPK
  • High Nitrogen Formula. Nitrogen aids in the formation of chlorophyll, encouraging vigorous growth for the development of a dense, attractive lawn.
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Compact soil can be identified by the amount of stagnant water in the soil. These will plug any potential holes aeration makes. You should also avoid aerating in the summer, as dry weather cakes the soil.

It is recommended that you apply four pounds of nitrogen fertilizer per 1000 square feet of lawn area. Do this during growth seasons for St. Augustine, every spring to summer.

Warm-Season Watering

Warm-Season Watering

It is important to water your plants well. It should not overflow, but your leaves should not be left to dry. This keeps soil from developing fungi. Water them during the early spring growing season.

Warm-Season Dethatching

Prevent over-thatching on your lawn to keep it from getting infected. Ensure to dethatch within the growing season for St. Augustine (early spring to early fall) for best results.


No matter how bad fungal infections may get, treating your St. Augustine grass lawn is always possible. The best treatment is to cut down your problematic patches before they spread.

If that is not enough, you can move to chemical fungicides. When in doubt, always ensure proper aeration, sufficient sunlight and proper lawn care to get rid of brown patch fungus.

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