St. Augustine Grass Diseases and Problems [Identification, Pictures + Fixes] | Lawn Model (2023)

We’ve all been there before- you wake up one day and your otherwise lush green St. Augustine lawn is spotting unsightly patches of brown or yellow grass. This- despite the fact that you’ve been mowing, watering, and fertilizing the lawn as necessary. So- what could be the issue here?

Well, St. Augustine grass- despite being relatively disease-resistant, is still vulnerable to a variety of fungal diseases, as well as pest infestations and competition from weeds. All these factors can affect the health of your St. Augustine turf, leading t it showing visible signs of turf stress. In this blog, we discuss St. Augustine grass problems in detail, including what causes them and how to fix these problems.

Signs St. Augustine grass has a problem

If your healthy St. Augustine turf is showing visible signs of stress, it could be as a result of a fungal disease, pest infestation, weed infestation, or any other applicable issues. You can identify your turf has a problem if you notice any of the following signs and symptoms:

St. Augustine Grass Diseases and Problems [Identification, Pictures + Fixes] | Lawn Model (1)
  1. Irregular brown spots- if you notice random patches of brown grass on your otherwise lush green St. Augustine lawn, you’re most likely dealing with a fungal infestation problem.
  2. Stolons turning brown- brown lateral runners/stolons are usually another pointer towards fungal infestations in St. Augustine turfs.
  3. Random yellowing of the grass blades- grass leaf yellowing can signify the presence of fungi, pests, weeds, or excessive shading.
  4. Browning at the base of the leaf blades- some types of fungi only cause browning at the base of the St. Augustine grass blades.
  5. Roots pulling out easily- if you can easily pull out some of the yellow/brown grass blades and the roots seem soft and spot a dark brown-black hue, you probably have a fungal issue.

Some of these signs and symptoms are usually the same, which is why you may want to consult a lawn professional if you’re unsure of what’s causing the problems on your lawn. For instance, it wouldn’t make sense to apply a fungicide when the problem is the presence of weeds or excessive shading.

Common St. Augustine grass diseases

St. Augustine grass is highly vulnerable to fungal diseases. The main types of fungi that tend to cause problems in St. Augustine lawns include take-all root rot fungi, brown patch fungi, gray leaf spot fungi, fairy ring fungi, and nigrospora stolon rot fungi.

St. Augustine Grass Diseases and Problems [Identification, Pictures + Fixes] | Lawn Model (2)

Each of these fungal diseases is discussed further below:

  1. Take-all root rot (TARR)

Take-All root rot typically occurs during the peak growth months of April and May, resulting in grass blade yellowing as the turf refuses to green up. However, since the yellowing of grass blades can also be caused by excessive shading, you can confirm that take-all root rot fungal infestation is the problem by pulling out a few blades of St. Augustine grass from the soil and noting how hard they are to pull. If the blades pull out easily, then take-all root rot might be the problem, as the disease causes the grassroots to decay and become soft.

To treat your St. Augustine turf of take-all root rot, we recommend applying a one-inch layer of sphagnum peat moss to cover up the affected lawn areas. You’ll want to avoid using fungicides for this particular turf disease, as they are not usually effective and the problem won’t go away.

  1. Brown Patch Disease

Unlike TARR which occurs during the peak growth season, brown patch fungi- also known as Rhizoctonia solani– are more likely to attack your St. Augustine lawn during fall and winter. This is because the extremely low nighttime temperatures during these seasons favor them. Excessive thatching and excessive soil moisture can also attract brown patch fungi.

As the name suggests, brown patch disease is usually characterized by dark brown patches occurring at the base of the leaf blades where stolons sprout from. You can also diagnose brown patch disease by pulling the affected blades from the attached runners to see if they pull loose easily. If so- then you have a brown patch problem.

To effectively treat brown patch disease and help your St. Augustine lawn to recover, it’s advisable to use a commercial fungicide with active ingredients like azoxystrobin, myclobutanil, and thiophanate methyl. Alternatively, you can take a proactive approach to prevent the disease before it occurs by ensuring proper soil aeration, good drainage, watering regularly, dethatching, and avoiding fertilizing during the cool seasons.

  1. Nigrospora Stolon Rot

Nigrospora sphaerica is a fungus that inhibits the proper absorption of moisture and nutrients by the St. Augustine grassroots, thereby causing the grass blades to turn yellow. You can identify this problem by examining the lateral runners that sprout from the base of the grass blades. If they’re decaying and have a dark brown color, then you probably have Nigrospora stolon rot fungi in your lawn.

Nigrospora stolon rot fungi are usually attracted to high temperatures and dry conditions. Therefore, you can prevent the problem by keeping your St. Augustine lawn adequately watered during the summer months. Meanwhile, treatment entails the application of a good-quality commercial fungicide.

  1. Gray Leaf Spot Disease

This St. Augustine fungal disease is characterized by dead patches of brown turf and typically occurs when conditions are hot and humid. Too much water and too much fertilizer in the soil can also provide appropriate conditions for the growth of the fungi that cause this turf disease. To treat gray leaf spot disease, you can use a fungicide containing at least two active ingredients such as azoxystrobin and thiophanate-methyl. However, fungicide treatments won’t be as effective as prevention by avoiding overwatering and over-fertilizing St. Augustine.

  • Fairy Ring Disease

Fairy rings occur as dark green circles of grass surrounded by an extra ring of dead grass and is caused by a species of soil fungi called basidiomycetes. These fungi tend to prefer sandy soils that have minimal moisture and soil nitrogen. Excessive thatching can also provide favorable conditions for basidiomycetes.

The mycelia of these fungi compete for the available soil nutrients with the turfgrass as they grow outwards. This, in turn, starves the desirable turfgrass- resulting in the rings of dead grass around the mycelia. Fairy rings are not only unsightly but also result in the formation of thick fungal mats that prevent the absorption of water into the ground.

You can treat fairy ring disease on your St. Augustine lawn by applying a fungicide, but this isn’t always the preferable approach, as fungicides contain chemicals that degrade the environment. A better treatment would be to remove the soil and turfgrass in the affected areas and re-sod as necessary. To do this, dig out affected sod areas by up to 12-inches deep, then refill the holes with fresh soil and re-sod as necessary.

Other St. Augustine lawn problems

As mentioned earlier, fungal diseases are not the only thing you’ll have to look out for if you have a St. Augustine lawn. While this turfgrass species is relatively pest-resistant, it’s highly vulnerable to a particular species of pests called chinch bugs. As these tiny bugs feed on your turfgrass, they let off a particular toxin that causes grass leaf blade chlorosis (yellowing).

Since chinch bugs are tiny and hard to spot with the naked eye, you can identify if they’re the cause of your lawn issues by using a pair of magnifying lenses to spot them. Chinch bugs are also attracted to high-temperature conditions, hence you’re most likely to spot them on your St. Augustine lawn during the summer months. You can easily control chinch bugs by applying a suitable insecticide/pesticide to the affected lawn areas.

The other non-fungal problem you’re most likely to encounter on your St. Augustine lawn is the presence of weeds. Despite being a weed-resistant warm-season turfgrass species, St. Augustine grass may still be vulnerable to weed invasions if you fail to properly water or fertilize the lawn. Doing so makes the weed plants and your turfgrass compete for and share the minimal moisture and nutrients available in the soil, causing the St. Augustine turf to starve.

You can easily identify common lawn weeds- such as dandelion, crabgrass, and dollar-weed- on your St. Augustine lawn- as they have bright flowers, and large leaves, and typically grow taller than the turfgrass. You can get rid of weeds on your lawn by manually pulling them out or applying a post-emergent herbicide to the affected lawn areas.


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What is wrong with my St Augustine grass? ›

Augustine grass is suffering. The main reasons are pests like grubs and chinch bugs, turf diseases like Brown patch and gray leaf spot, poor soil quality, and excessive fertilizer applications.

What does fungus look like on Saint Augustine grass? ›

How To Control And Treat Fungus In St. Augustine Grass (Brown Patch ...

What causes disease in St Augustine grass? ›

Augustinegrass caused by Pyricularia grisea. Gray leaf spot is a fungal disease (caused by Pyricularia grisea) that occurs most commonly on St. Augustinegrass (Stenotaphrum secundatum), but occasionally may also be found infecting tall fescue, bermudagrass, centipedegrass, and ryegrass in home lawns.

How do you treat St Augustine fungus? ›

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.

What does grub damage look like in St. Augustine grass? ›

Grubs: Damage shows up in the spring. CRITICAL SYMPTOMS: Grass pulls loose easily from the soil because roots have been eaten by the white grubs (If you dig several square-foot patches in the afflicted areas you will see 5 or 6 grubs per square feet. If you encounter only one or two, grubs are not the cause.

What does grub damage look like in St. Augustine? ›

White grub worm damage is usually evident in early spring, as grass fails to green up after winter. Affected grass will pull loose easily from the soil, dead blades and runners intact. Those symptoms are similar to TARR, but you will find large, white grubs in quantity if you turn the soil in affected areas.

Why is my St. Augustine grass turning yellow and dying? ›

Some possible causes for St. Augustine Grass to turn yellow include iron deficiency due to high pH and phosphorus levels, fungal diseases that cause yellow patches or root rot, excessive nitrogen, nitrogen deficiency, over-watering or heavy rain, and high temperature.

How do you fix patches in St. Augustine grass? ›

If your grass is a St. Augustine grass lawn, you'll want to sod or plug your bare spots. Purchase a few pieces of sod or enough plugs to cover your bare spots from your local garden center. Then prepare the area by applying a generous layer of Scotts® Turf Builder® Lawn Soil.

How do you treat all patches in St. Augustine grass? ›

No fungicides cure the disease, and there are no resistant grasses. To prevent the disease or slow its spread, keep the grass at least 4 inches high, mowing no more than 1/3 of the blade at a time. Water regularly. Deep, infrequent waterings are better than frequent, shallow ones.

What does brown patch look like in St. Augustine grass? ›

With brown patch disease, symptoms begin as 6-12 inch diameter off color patches that turn yellow, then reddish-brown, then brown to straw-colored (see photo). These patches may merge and may expand several feet in diameter. Often, there may be rings of yellow/brown turf with green centers.

Why does my St. Augustine grass have brown patches? ›

Augustine lawn has developed circular patches of dead, brown areas of turf, then the most likely cause for these brown patches will be a lawn fungus disease called Brown Patch, or Large Patch Fungus.

How do you treat grass fungus? ›

  1. Correct your watering regime.
  2. Water in the early morning instead of the evening.
  3. Remove grass clippings after you mow (otherwise, you'll spread the disease).
  4. Remove excessive thatch buildup.
  5. Mow the lawn regularly.
  6. Apply a fungicide in the affected area.
Jun 19, 2022

What is the best fungicide for brown patch? ›

Headway® fungicide is an excellent choice for preventive control of brown patch. Headway contains the active ingredients azoxystrobin and propiconazole and delivers broad-spectrum control of brown patch, as well as all major turf diseases.

How do you treat brown patch fungus? ›

Many cases of brown patch can be cured simply by improving air circulation in the lawn, which reduces the humidity that favors the fungus. The best way to do this is to aerate and dethatch the lawn annually.

How do you revive St. Augustine grass? ›

Water St. Augustine grass with 1-1.5 inches of water every week to revive it quickly. Apply nitrogen fertilizer and grub control, then mow the lawn high at 3 inches to make the grass green again. If the grass is dead, install new sod to revive and bring the lawn back to life.

What is a natural remedy for lawn fungus? ›

Mix one tablespoon of baking soda with a gallon of water. Spray affected areas every three days until the mold or fungus is gone. These last two options work to both smother some plant pests and keep fungus in check. Horticultural oil is safe for use on lawns, turf and plants.

Why is my St. Augustine grass turning yellow and dying? ›

Some possible causes for St. Augustine Grass to turn yellow include iron deficiency due to high pH and phosphorus levels, fungal diseases that cause yellow patches or root rot, excessive nitrogen, nitrogen deficiency, over-watering or heavy rain, and high temperature.

Why is my St. Augustine grass dying? ›

St. Augustine grass can turn brown and die due to drought stress, fertilizer burn, dormancy, poor soil quality, or grub damage. A brown St. Augustine lawn that appears dead can also be a sign your grass is still in dormancy or is suffering from frost burn.

How can you tell the difference between a chinch bug and a brown patch? ›

The easiest way to tell the difference is that brown patch tends to manifest in a circular pattern while chinch bug damage is irregular in shape.

Why are the blades of my St. Augustine grass turning yellow? ›

ANSWER: This yellowing is likely due to all of the rain. Rains leach nitrogen out of the soil, which causes some yellowing. Also, when the soil stays wet, grass roots are stressed and don't work as well. So the roots may not be properly absorbing minerals like nitrogen from the soil.

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