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

Fungus on St. Augustine grass shows symptoms such as browning of leaf blades, rust-like growths on grass, and areas of thinning or dead grass in your lawn. The good news for you is that brown patch disease on St. Augustine grass can be treated easily even using DIY methods as I’ve described in this article.

You can treat fungus in St. Augustine grass naturally by cutting out areas in your lawn that are infected if the disease has not spread to large patches. Another way to get rid of lawn fungus is by applying anti-fungal treatments such as azoxystrobin, flutolanil, Consan 20 or thiophanate-methyl.

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While this warm-season grass is known to be somewhat resistant to fungal diseases, your St. Augustine lawn is still susceptible to fungus- especially under prolonged wet and shady conditions. Whether it’s Pythium blight or rhizoctonia large patch, you can always get rid of any type of fungi invading your lawn.

Signs of Fungus on St. Augustine Grass

First, it is important to identify the problem because there are possibly other reasons for browning and dead spots including grub infestation in a lawn. Signs of fungus on St. Augustine lawn include:

• Stolons start to turn brown.
• Brown spots and patches on your lawn.
• Yellowing of grass blades in a random pattern.
• Dark brown fungal threads covering the stolons and crowns of grass.

Fungal diseases on St. Augustine grass manifest themselves in the form of irregular brown spots. In terms of size, these circular spots can go anywhere from a few inches to several feet in diameter. However, this appearance may vary depending on the soil conditions.

Additionally, if it’s a fungal problem that’s gone untreated for a while, the inner part of the grass patches may recover and regain their green color, with rings of dead grass surrounding them.

When under fungal disease attack, St. Augustine grass blades that occur near the ground’s surface tend to spot a dark-brown color along the edges and irregular tan spots that resemble a burnt-up cigarette.

If you’re unsure as to the cause of the burns on your St. Augustine grass (other common causes include grubs and pet urine), your best option would be to consult a lawn-care professional.

Alternatively, you can call your local county extension offices, as they’re usually in possession of local laboratory listings. You can send a soil and grass sample from your lawn to one of these labs to be tested for fungal infection.

Causes of Brown Patch Disease

Your lawn is more likely to suffer from fungal diseases under certain harsh weather conditions including high humidity and extreme precipitation. As such, homeowners in Coastal regions like Florida and California are more likely to experience brown patch disease on their lawns.

In general, the common causes of brown patch disease in St. Augustine lawns are:

• Prolonged periods of wetness especially in shaded areas (common in summer).
• Overfertilizing and overwatering your lawn.
• Too much shade.
• Compacted soil

Mild daytime temperatures of between 70-90 degrees Fahrenheit and cool nights also provide perfect conditions for the spread of brown patch disease on St. Augustine lawns.

Poor lawn maintenance also provides the perfect conditions for brown patch fungi to invade your lawn. Lawns that are scarcely watered during spring-summer and lawns that experience high-foot traffic leading to soil compaction are, thus, more likely to be infected with brown patch fungal disease.

How to Treat St. Augustine Grass Fungus

Effective treatment of brown patch fungal disease on St. Augustine grass depends on the exact type of fungus. Once you identify the exact type of fungus affecting your lawn, you can apply the right treatment for the lawn fungus.

Here’s how to get rid of St. Augustine grass lawn fungus:

1. Replace affected grass with new sod

This DIY treatment method is best for fairy ring fungus – a type of grass fungus that manifests itself as a brown ring of dead grass enclosing a dark-green patch.

Fairy ring fungus can be treated through the removal of any white soil sections on the outer parts of the rings. Once you’ve removed the affected areas, refill the excavated lawn area with a fresh layer of St. Augustine grass sod.

2. Apply azoxystrobin to kill fairy ring fungi

If you notice your lawn showing symptoms such as a circular pattern of mushrooms, overgrown grass or dead grass, you need to treat fairy ring disease. The best treatment is to spray anti- fairy ring fungicides like azoxystrobin and flutolanil on your infected lawn.

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

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3. Treat grey leaf spot fungus using thiophanate-methyl 

Grey-leaf is a fungal disease characterized by irregular bleached-out patches on your turfgrass and is caused by high humidity levels and over-fertilization. Treat it using high-quality fungicides, including thiophanate-methyl and azoxystrobin.

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4. Alternate anti-fungal products

Grease spot fungus- also known as Pythium blight, this type of fungal infection is characterized by greasy and sticky leaf blades on your St. Augustine turf.

Effective treatment of Pythium blight involves the alternate use of various anti-fungal brand products such as the Southern AG Fungicide below; since this fungus is renowned for becoming resistant to treatment after some time.

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Prevention

While St. Augustine grass fungus is treatable, as shown above, the best and most cost-efficient way to keep this grass disease off your lawn is through prevention.

Effective prevention includes facilitating conditions that hinder fungal infection and minimizing/eliminating conditions that fuel the same. Follow these steps to prevent grass fungi from creeping into your beautiful lawn:

Reduce soil compaction

Lawn soil that is too compact is more susceptible to fungal diseases. As such, you can reduce the chances of infection on your St. Augustine lawn by using a plug aerator to de-compact high traffic areas.

Typical signs of compact soil include runoff water and standoff water. Aeration should- however- be avoided during summer.

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Important: When to Aerate Your Lawn

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Boost the soil’s nitrogen levels

Lawn soil that’s rich in nitrogen is less-susceptible to fungal infections. You can boost the soil nitrogen levels on your St. Augustine lawn by leaving behind the grass clippings whenever you mow- instead of raking them away.

Alternatively, you could use nitrogen-rich fertilizers to boost the soil’s nitrogen levels. Such as the Simple Lawn Solutions Lawn Food seen here…

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Lawn-care experts typically recommend the application of about four-pounds of nitrogen fertilizer for every 1000-square feet of lawn space.

This should also only be done during the growing seasons for St. Augustine grass (spring-summer), being as it’s a warm-season grass species.

Warm-season watering

Water optimally to avoid dry soil conditions that facilitate fungi, ensure to water your lawn at dawn during the growing seasons for St Augustine grass which is around spring-summer.

Warm-season dethatching

Overly-thatched St. Augustine grass lawns are more susceptible to fungal infection. You should- therefore- ensure to dethatch your lawn during the active growth season for St Augustine grass (spring to early fall).

Also See: Dethatching vs. Aerating

Brown Patch Disease - St Augustine Grass

Sources

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