St Augustine grass makes a dark green turf that is appealing to any homeowner. It is a low-maintenance grass but is susceptible to diseases and insects. Indicators of a problem in St Augustine grass include brown patches, circular patches in the lawn, yellow patches, thin turf, and straw-colored spots.
Some diseases that attack St Augustine lawn include; take all root rot, grey leaf spot, nigrospora stolon rot, and brown patch.
St Augustine Grass Problems and Diseases
The following are major problems and diseases that affect St Augustine grass and what you should do.
1. Take-all root rot (TARR)
Take-all root rot is a severe disease caused by a fungus known as Gaeumannomyces Graminis var. The condition commonly affects St Augustine and Bermuda grasses, where it is referred to as Bermuda decline. The disease causes weak, brown, and dead patches on the turf.
The fungi live in the soil and could be present in any St Augustine or Bermuda lawn. Identifying the disease is paramount as you will treat it and go back to enjoying a lush lawn. However, misdiagnosis is widespread as the disease will make the grass yellow and can be mistaken for nutrient deficiency or chinch bug invasion.
To identify the disease, look for a yellowing blade that later turns brown and wilts. If untreated, the condition will eat up all the grass, leaving bare patches on the lawn. The disease will cause the stolon and roots to rot. The roots will turn blackish and weak, and you can pull the grass out with little effort.
TARR is likely to affect the shaded part of your lawn, so to prevent it from recurring, do the following:
- Remove anything shading your grass
- Aerate your lawn if the soil is compacted.
- Mow properly.
- Improve soil drainage.
- Use herbicide properly- excessive use of herbicide can injure the grass, making it vulnerable to lawn diseases.
- Dethatch your lawn- too much thatch encourages fungal diseases.
- Water appropriately- over watering or underwatering increases the risk of TARR.
- Use fungicides such as azoxystrobin, myclobutanil, or propiconazole and follow manufacturer instructions on application and watering in.
- Cover the affected area with a layer of sphagnum peat moss.
2. Grey Leaf Spot
Grey leaf spots appear as oval and round spots on the grass blade with dark brown borders. It is a fungal infection caused by the fungus Pyricularia Grisea. The fungus thrives in shaded, hot, and humid areas. The disease is triggered by high temperatures, nitrogen deficiency, excessive fertilizer use, and overwatering.
- Water appropriately and improve soil drainage by ensuring your soil is not compacted.
- Do not plant St Augustine grass in a shaded area. Instead, plant shade-loving grass or cut down the trees causing the shade.
Use a fungicide containing azoxystrobin, pyraclostrobin, or fluoxastrobin.
3. Nigrospora Stolon Rot
The disease is caused by the fungus Nigrospora sphaerica. It usually attacks the stolon area of the grass and stops the movement of water and nutrients to the leaves. The blades will wilt, turn yellow, and then die.
The disease is severe mainly during summer and spring as high temperatures, and drought conditions encourage stolon rot.
Apply a commercial fungicide. Also, ensure to water the lawn appropriately to prevent the disease from recurring.
4. Fairy ring disease
The morning after a warm night of heavy rain and high humidity, you may notice a dark green ring appear on your St Augustine lawn. It is caused by the fungus Basidiomycetes by altering the soil properties in the ring.
The disease can also be caused by the accumulation of toxins in the root system. Grass growing on sandy soil with little moisture and excess thatch are more susceptible.
- Dethatch the lawn.
- Apply nitrogen fertilizer to the ring to encourage root growth.
- Water the lawn.
- In severe cases, treat the lawn with a fungicide.
5. Brown patch
Brown patch is caused by the fungus Rhizoctonia solani and usually affects St Augustine grass in spring to late winter. The disease causes brown patches on the lawn.
Use fungicides for treating brown patches such as myclobutanil, Thiophanate methyl, and azoxystrobin.
The disease thrives in wet soil with hot and humid weather. Ensure the soil is well draining and watered appropriately. You can also do dethatching and soil aeration to counter-compaction.
6. Chinch bugs
They are tiny insects that will usually strike in summer. They are red when young but change to black with a white spot as they grow. The insects lay their eggs on the lawn, and even after killing them, the eggs are left and will hatch into a new generation.
The insects suck the juice out of the grass, causing irregular brown patches, which will later die.
Use insecticide to kill chinch bugs.
- Doing proper lawn maintenance will keep chinch bugs off your lawn.
- Ensure the soil on your lawn is well draining.
7. St Augustine Decline (SAD)
It is a viral disease caused by Panicum mosaic virus that affects St Augustine and Centipede grass. Initial symptoms are mild chlorotic, mottling, or stippling of grass blades. The blades will turn yellow and thin, then die out.
The disease can be brought to the lawn by contaminated sod or tools such as mowers or dethatchers. The condition has no cure, but you can prevent it by making sure anything that comes to the lawn is not contaminated.
How to Revive St Augustine grass
St Augustine grass lawn usually browns when in dormancy during winter. It can also brown or die due to drought stress, poor soil quality, diseases, pest infestation, or fertilizer burn. Brown grass does not necessarily mean the lawn is dead.
To revive the lawn, you must first identify what is killing it and then treat the problem. Below is how you can revive your St Augustine lawn:
1. Treat a diseased lawn
You need to identify the actual cause and treat it effectively. For fungal diseases, treat with fungicides and insecticides for harmful insects.
2. Water the lawn adequately
If your lawn is dying from drought stress, water the lawn twice a week with one inch of water until the grass comes out of dormancy. Moving forward, water with ¾ inch once per week.
3. Test your soil
Your grass could be dying from insufficient nutrients, compacted soil, or excess salts from over-fertilization. Fortunately, you can find many soil test kits online. The Soil test kit I’ve linked to above works well.
- Insufficient nutrients– Test the soil and fertilize it with the missing nutrients.
- Soil compaction– Dethatch and aerate the lawn.
- Excess salts from over-fertilization – Water the lawn with one inch of water per day for seven days to flush out the excess salts, especially in the burnt areas
4. Resod the lawn
If some patches are dead and the reviving method does not work, it might be time to resod the lawn. Ensure to first treat the initial cause before resoding.
St Augustine grass makes a beautiful lawn but is affected by fungal diseases and insects. Before reviving the lawn, you must treat the disease and test the soil. If the damage is severe, you might need to resod the lawn.
- Clemson University: GRAY LEAF SPOT ON ST. AUGUSTINEGRASS
- Richard L. Duble, Turfgrass Specialist, Texas Cooperative Extension, St. Augustine Decline
- University of Florida, Summer Lawn Diseases