How to Treat St. Augustine Grass Fungus & Get Rid of Brown Patches in Lawn

My St. Augustine lawn showcased lush growth until a few days ago. I’ve noticed brown patches cropping up all over my turf, which I suspect are signs of a fungal disease, sometimes called brown patch fungus.

If your st augustine grass is affected by leaf spots or any other common types of fungus like take-all rot, there’s no need to break a sweat just yet because I’ve listed several tried and tested ways to bid adieu to grass fungus from your turf.

You’ll find out more details on how to perform these tasks effectively below.

How to Treat Grass Fungus in St. Augustine Lawns?

Now you’re probably thinking that applying a fungicide from Home Depot or from your nearest garden center in favorable conditions is the best way to treat St. Augustine grass fungus and even though this is partially true, it will fix the underlying problem causing the fungus to appear.

That said, here’s what you need to do before applying any fungicide applications:

• Proper Watering – St. Augustine grass prefers about 1 to 1.5 inches of water per week and deep and infrequent watering. The best time to water your St. Augustine lawn is in the early morning, which gives your grass enough time to dry by the evening. But remember, no amount of fungicide will control any lawn fungus that results from poor watering practices.
• Improving Drainage – Ensure good soil drainage to prevent waterlogging, which can create conditions favorable for fungal growth. There are many ways lawn owners can fix drainage issues to prevent fungal infection and other lawn problems including improving soil structure, leveling low spots, aerating the soil, and installing drainage pipes. 
• Fertilization – Follow a balanced fertilization schedule based on soil test recommendations. Avoid excessive nitrogen fertilizer applications, as over-fertilization can increase the chances of fungal diseases. 
• Mowing Practices –  Set your mower at the recommended height for St. Augustine grass, which is typically between 2.5 to 4 inches. Most importantly, keep mower blades sharp to ensure clean cuts and minimize stress on the grass. Avoid removing more than one-third of the grass blade in a single mowing session.
• Fungicide applications – The good news is that there are myriad different fungicides available to cure the brown areas in your lawn after of course, you apply the right cultural practices. But before using any type of fungicide, it’s important to determine the type of fungus you’re dealing with. Once you’ve figured out which fungus has affected your lawn, but an appropriate fungicide and apply it according to the manufacturer’s directions on the label. Here are three of my go-to options in the lawn fungicide space.

Best Grass Fungus Herbicide for St. Augustine Lawns

1. BioAdvanced Fungus Control for Lawns

The BioAdvanced Fungus Control for Lawns comes with an insect killer so you can tackle two problems at once. This insect killer can kill grubs, ants, and ticks and can relieve your lawn from chinch bug damage. After application, the fungicide provides 30-day protection and will not wash off during rainy weather. 

2. Southern Ag Liquid Copper Fungicide

Another hit in the lawn fungicide segment, the Southern Ag liquid copper fungicide can control lawn disease caused by bacteria and fungi. It can even control moss and algae and is easy to use with hose end sprayers.

3. Spectracide Immunox Multi-Purpose Fungicide Spray

With the Spectracide Immunox Multi-Purpose Spray, you get both disease and pest protection for your lawn. This multi-purpose formula cures and prevents all major diseases and should be mixed with water before application. It can’t be washed off by rain once the spray is dry. 

What Causes St. Augustine Grass Fungus?

There are several causes for fungus in your St. Augustine lawn, most notably: 

• Over-watering lawn leads to excess moisture – standing water from over-watering can promote the growth of lawn fungus, mostly in the early or late spring.
• Temperature change – you’ll typically notice lawn fungus in the spring season owing to all the fluctuations in temperature. While spring is a season of good growth and blossoming, it can also be a good time for lawn fungus to call your lawn home. 
• Poor Air Circulation – insufficient air circulation around the grass blades can contribute to the development of fungal diseases. This is more likely to occur in densely packed lawns, where air movement is restricted.
• Improper Mowing – cutting the grass too short or using dull mower blades can stress the grass and make it more susceptible to fungal infections. You should always aim to mow at the appropriate height for your grass type and with sharp mower blades.
• Poor Soil Health – unhealthy or imbalanced soil can weaken the grass, making it more susceptible to diseases. Regular soil testing and proper fertilization can help maintain optimal soil health.
• Fungal Spores from Nearby Areas – fungal spores can be carried by wind, animals, or equipment from nearby infected areas. Once introduced to a lawn, these spores can establish and cause an infection. Follow this guide to assess and address compact soil in your yard. 

Common Types of St. Augustine Grass Fungus

While several different types of fungus can affect lawns, the most common types of fungus you’re bound to encounter in your St. Augustine grass turf include: 

1. Brown Patch Disease (Rhizoctonia solani) – Brown patch is one of the most common fungal diseases affecting St. Augustine grass. It typically appears as brown circles, sometimes irregular patches of brown spots, or tan grass with a darker border. The affected areas of small and large patches can range from a few inches to several feet in diameter in severe cases. Brown patch is often more prevalent during periods of high humidity and warm temperatures.
2. Gray Leaf Spot (Pyricularia grisea) – Gray leaf spot is characterized by small, grayish lesions with darker borders on a leaf blade. As the disease progresses, the lesions can merge, leading to widespread damage. This fungus is favored by warm and humid conditions, and it tends to be more prevalent in lawns with poor air circulation.
3. Take-All Root Rot (Gaeumannomyces graminis var. graminis) – Take-all root rot is a common disease that affects the roots and stolons of St. Augustine grass, causing yellowing, wilting, and thinning of the turf. Infected roots become blackened and rotted. This disease is often associated with poor drainage and acidic soil conditions and can affect your lawn in the early fall or late fall or anywhere in between. 
4. Large Patch (Rhizoctonia solani) – Large patch, also known as brown patch appears as large, irregular patches of discolored turf, ranging from yellow to brown and or dead spots. Large patches are more prevalent during the fall and spring when temperatures are cooler.
5. Fairy Ring (Various Fungi) – Fairy ring is caused by different species of fungi that form visible rings or arcs of dark green grass. The outer edges of the ring may have mushrooms or puffballs. This fungus does not directly harm the grass, but it can disrupt the aesthetic appearance of the lawn. Learn more about fairy ring fungus.

Before You Go…

If you aren’t sure what causes lawn fungus and the best fungus treatment for grass, my detailed article on fungus treatment for grass will provide some great insights. Make sure to identify what type of fungus is impacting your lawn first, so you can apply the right treatment to your grass.

---

References

• Clemson University: College of Agriculture, Forestry and Life Sciences: GRAY LEAF SPOT ON ST. AUGUSTINE GRASS

---