How Do You Get Rid of St. Augustine Grass Fungus (Brown Patches)?

Do you have St. Augustine grass growing on your lawn and have started noticing signs of turf stress lately? Do you suspect that the turf damage is due to fungal infestation but aren’t 100% sure? Brown patches or burnt out turf sections on St. Augustine lawns could be as a result of various factors, including fungal infestation, pest infestation, weed invasions, excessive shading, and so on.

Therefore, to be sure that the problem you’re dealing with is a fungal disease, you need to know the signs and symptoms for identifying fungus on St. Augustine grass. We discuss these identification signs and more in this blog, complete with a section on how to get rid of various types of lawn fungi.

Signs of fungus in St. Augustine grass (Identification)

The signs and symptoms of fungus on your St. Augustine lawn may vary depending on the specific type of fungi that have invaded the lawn. Below, we go through the signs and symptoms that indicate the presence of various common lawn fungi:

  1. Identifying brown patch disease

Brown patch species of fungus normally attacks the base of the grass blades close to where the plants meet the soil. As a result, the base of the leaf blades rot and have a distinctive dark shade. You can also sense a decaying smell if you pull out the affected blades and hold them close. Meanwhile, you’ll also notice that the affected leaf blades tend to pull away from the plant without much resistance. The roots, however, usually won’t show any signs of damage.

After a while, the problem spreads from the base of the grass blades t the rest of the blades, resulting in reddish-brown patches as the leaves die. With time, these brown patches can extend for up to several feet in diameter, leaving you with an unsightly lawn.

  1. Identifying dollar spot disease

Dollar spot is a lawn fungal disease that’s characterized by random, circular patches that are about three-inches in diameter. You may also notice tan-colored lesions on the edges of individual grass leaf blades, each surrounded by brown or purple rings. The fungi that cause this disease also produce fungal threads that are grayish-white and fluffy in texture.

  1. Identifying gray leaf spot disease

During the earlier stages of invasion, you can tell that gray leaf spot fungi are present on your St. Augustine turf if you notice that some of the individual grass leaf blades are spotting tiny, brown spots. After a while, these spots usually enlarge into circular, tan-colored spots with brown margins. In highly humid conditions, you’re likely to notice the spots turning gray, as the fungi produce spores at the center.

Since gray leaf spot fungi attack sections of individual leaf blades, it’s not immediately noticeable as there are no dead-giveaways in the form of large brown patches. However, you may notice that the turf is thinning out, much in the same way as it would when undergoing drought stress.

  1. Identifying fairy rings

Fairy rings on St. Augustine lawns are characterized by zones of dead, brown grass surrounded by dark-green zones. You may also identify this disease if there are mushroom mycelia growing in rings in close proximity to these dead spots.

  • Identifying Pythium blight disease

During the early stages of this fungal diseases, sections of your St. Augustine turf will assume a gray tan and a wilted appearance. As the fungi advance, you’ll begin noticing brown and matted spots on your turf, which may be surrounded by bronze-colored grass blades on the edges.

  • Identifying take-all root rot disease

The earliest sign of take-all root rot is when sections of your turf turn light green- yellowish, instead of the dark green hue that you’ve become accustomed to. After a while, if you pull off the stolons and roots of individual grass blades in the affected areas, you’ll notice black-colored lesions and root rot. The decaying of the roots causes the affected grass plants to die, leaving behind bare spots on the lawn.

What causes brown patch disease?

Of all St. Augustine grass fungal diseases, brown patch causes the most damage to turfs, as it leaves behind large sections of unsightly brown patches over a short period of time. The disease is caused by Rhizoctonia fungus, which finds nitrogen-deficient lawns more favorable. Rhizoctonia also prefer hot and humid conditions, hence the disease advances more rapidly when temperature conditions rise to about 80-degrees Fahrenheit.

During fall, Rhizoctonia fungi usually hide out in the grass thatch. The cold temperatures and high humidity during this time of the year favors them. As such, once the temperatures drop below 80-degrees Fahrenheit, these fungi start penetrating the grass blades via the stomata, causing stress damage in the process. These fungi are also more likely to appear on your lawn if there’s excessive soil moisture due to rainfall or irrigating too frequently. As such, you can make your St. Augustine turf less-vulnerable to brown patch disease by avoiding overwatering and ensuring proper soil drainage.

How to get rid of St. Augustine grass fungus

The most common types of fungal diseases that affect St. Augustine grass-turfs include brown patch, dollar spot, gray leaf spot, Pythium blight, fairy rings, and take-all root rot. We discuss how to eliminate the fungi that cause each of these lawn diseases below:

  1. Getting rid of Brown Patch

The fastest and most effective way to eliminate brown patch fungi from your St. Augustine lawn is by applying a fungicide. Whichever brand of fungicide you opt for, you should ensure to follow the manufacturers’ instructions on the product packaging for maximum efficiency and safety. Remember, however, that fungicides are most effective on brown patch when applied early on at the onset of the disease. For late applications after the disease has advanced, repeat applications may be necessary to completely get rid of all the fungi.

  1. Getting rid of Gray Leaf Spot

Usually, the best way to control gray leaf spot disease is by maintaining a proper maintenance regimen that includes regular mowing, dethatching, core aeration, and infrequent irrigation. However, if you’ve tried all these and still have this fungal problem on your lawn, it may be time to go for an appropriate fungicide. Examples of effective fungicides include Azoxystrobin, Pyraclostrobin, and Fluoxastrobin. Finally, you’ll want to avoid using any of these products exclusively in the long run, as gray leaf spot fungi usually grow resistant to them. A good idea would be to alternate them.

  1. Getting rid of Dollar Spot

Usually, post-emergence fungicides are very effective at controlling dollar spot fungi, hence minimizing the need to apply pre-emergence fungicides. For maximum efficiency, however, you should apply the fungicides as soon as you notice its signs and symptoms on your St. Augustine lawn.

  1. Getting rid of Pythium Blight

Pythium blight is a fungal disease also known as grease spot. To kill off grease spot fungus and prevent them from causing further damage to your St. Augustine grass blades, consider using common anti-fungal treatments like Azoxystrobin and myclobutanil. However, you may have to alternate their use as this fungus tends to develop resistance if an exclusive fungicide product is used on it every time.

  • Getting rid of Fairy Ring

The best way to get rid of fairy ring fungus is to replace the affected lawn sections with new St. Augustine sod. This is a more eco-friendly option compared to use of chemical fungicides. All you have to do is dig out the affected soil sections and refill the excavations with fresh sod. However, if you find this option to be too labor-intensive and time-consuming, you can opt for an appropriate fungicide such as flutolanil or Consan 20. For maximum efficiency, pick a fungicide product that combines at least two of these active ingredients.

  • Getting rid of Take-All Root Rot

Take-all root rot fungi thrive in highly alkaline soil conditions, hence you can control this disease by gradually lowering your soil pH to be slightly acidic. To do this, simply apply ammonium sulfate mixed with peat moss at a rate of five pounds per 1000 square feet every year.

However, since such soil treatments are gradual and slow, you can get rid of take-all root rot faster by using appropriate fungicides, which include myclobutanil and propiconazole. For St. Augustine lawns, the above fungicides are best applied during spring and fall. It’s also advisable to water your lawn after application of these fungicides to ensure the products penetrate into the root zones and the soil to kill the fungi.

Best fungicide for brown patch in St Augustine lawns?

Brown patch fungi are quite stubborn and cannot be wiped out with only a single application of fungicides. As such, you should ensure regular application of the appropriate anti-fungal treatments such as thiophanate-methyl or propiconazole. While doing so, ensure to follow the manufacturer’s instructions on frequency of application for maximum effectiveness. For instance, when using thiophanate-methyl anti-fungal products, you should apply no less than 6.75 pounds for every 5000 square feet of lawn area every 14-21 days.  

Common types of fungus affecting St. Augustine grass lawns

The following are some of the common types of fungus responsible for causing the fungal lawn diseases that we’ve discussed in previous sections:

  1. Rhizoctonia fungus- which causes brown patch disease and may inhabit the soil for a while before causing visible damage to your St. Augustine turfgrass. Rhizoctonia fungus can stay inactive in the lawn thatch until conditions become favorable.
  2. Sclerotinia homeocarpa– which is the fungal species that causes dollar spot disease. When conditions are favorable, the spores of this soil-inhabiting fungus usually become active, causing the dollar spot disease to manifest itself.
  3. Pyricularia grisea– which is the fungal species responsible for gray leaf spot disease and prefers warm and moist conditions. Interestingly, St. Augustine is the only warm-season turfgrass that’s vulnerable to this fungus.
  4. Pythium fungus- which is known to cause Pythium blight- also called grease spot disease. The spores of this fungus are usually transported across the lawn as runoff water drains through the St. Augustine turf.
  5. Basidiomycetes- which is the family of soil fungi that cause fairy ring disease in St. Augustine grass. Basidiomycetes usually trigger turf damage by depleting nutrients in the soil and releasing a toxic by-product that harms the turfgrass upon contact.
  6. Gaeumannomyces graminis– which is the species of fungus responsible for causing take-all root rot disease. This soil-inhabiting fungus also loves to make a habitat out of St. Augustine stolons and lawn thatch that lies between the topsoil and the base of the grass blades.

Can the grass recover from fungus?

After you’ve completely rid your St. Augustine turf of disease-causing fungi, the visible signs of damage will still be present on the turf. Luckily, you can help your turf recover to its lush green, healthy appearance by doing the following:

  1. Adopting proper irrigation practices- avoid watering your St. Augustine lawn at night and instead do so in the morning. Daytime watering is less attractive to the growth and reproduction of fungi.
  2. Mowing at the proper height- a well-maintained lawn that’s mowed at the appropriate height will have enough natural defenses to keep off fungal damage. A good height for mowing St. Augustine grass is between 3-4 inches.
  3. Aerating and overseeding- core aeration prior to overseeding during early fall is recommended to help your turf recover from summer stress and stay healthy enough to keep off fungal diseases.



Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top