Brown Spots On St Augustine Grass

If you’re seeing brown spots on St Augustine grass, you know how quickly they can spoil your lawn’s lush green look. This common problem has several causes, but the good news is that most are treatable. Let’s look at what might be going wrong and how you can fix it for good.

Brown patches can appear for many reasons. It might be a simple issue like dull mower blades tearing the grass. Or, it could be a sign of a serious fungal disease. Sometimes, insects or poor watering habits are to blame. The first step is always to figure out the real culprit. A correct diagnosis saves you time, money, and a lot of frustration.

This heading describes the main visual problem you’re facing. It’s a symptom, not a cause itself. To treat these spots effectively, you need to play detective. Look closely at the pattern, the time of year, and the condition of individual grass blades. Your investigation will point you toward the right solution.

Common Causes of Brown Spots

Not all brown spots are created equal. Here are the usual suspects:

Fungal Diseases: This is the most frequent cause. Diseases like Brown Patch, Gray Leaf Spot, and Take-All Root Rot thrive in warm, humid conditions and can spread fast.
Insect Damage: Chinch bugs and white grubs feed on St. Augustine grass. Chinch bugs suck sap from blades, while grubs eat the roots underground. Both leave behind dead, brown areas.
Watering Issues: Both too much and too little water cause stress. Overwatering creates soggy soil where fungus grows. Underwatering simply dries the grass out, starting in patchy spots.
Soil Compaction: When soil is too hard, air, water, and nutrients can’t reach the roots. The grass weakens and turns brown, especially in high-traffic areas.
Dull Mower Blades: Blades that rip instead of cut leave frayed, brown tips on each grass blade. This makes your whole lawn look dull and can invite disease.
Pet Urine: The high nitrogen concentration in dog urine can burn the grass, leaving distinct brown spots with surprisingly green rings around them.

How to Diagnose Your Brown Spots

Take a walk across your lawn and observe carefully. Ask yourself these questions:

What’s the Pattern? Are spots circular, irregular, or along edges? Fungal spots often start as circular patches. Insect damage may appear more scattered.
Is the Grass Dead or Dormant? Try the “tug test.” Grab a handful of brown grass and pull gently. If it comes up easily with no roots, insects or rot might be the problem. If it’s firmly rooted, it might be dormant or stressed.
Check the Blades: Look for lesions, spots, or rotted sheaths at the base of the plant. Fungal diseases leave clear marks on the grass blades themselves.
Look for Bugs: Part the grass at the edge of a brown spot and look at the soil and base of the grass. Chinch bugs are tiny and black with white wings. You might also see their red nymphs.
Consider the Weather: Has it been very wet, humid, or dry lately? Weather is a huge clue for fungal or drought stress.

Effective Treatment Solutions by Cause

Treating Fungal Diseases

Fungus requires a targeted approach. First, identify the specific disease, as treatments vary.

Improve Air Flow: Trim back overhanging branches and shrubs to allow sunlight and air to dry the grass faster.
Water Wisely: Water deeply but infrequently, and only in the early morning so grass dries by nightfall. Avoid evening watering at all costs.
Apply Fungicide: For active outbreaks, use a labeled lawn fungicide. Products containing azoxystrobin or propiconazole are often effective for Brown Patch. Always follow the label instructions exactly for application rates and timing.
Reduce Nitrogen: Avoid high-nitrogen fertilizers in peak summer heat, as this can fuel fungal growth.

Eliminating Insect Pests

For chinch bugs, confirm they are present with a simple test. Cut the bottom out of a metal can, push it into the soil at the edge of a brown patch, and fill it with water. If chinch bugs are present, they’ll float to the top within minutes.

Use an insecticide labeled for chinch bugs or lawn grubs. Bifenthrin or carbaryl are common active ingredients.
Water the lawn lightly before application unless the label says otherwise. This brings insects closer to the surface.
Apply the product, then water it in lightly to move it into the thatch layer where bugs live.
For grubs, treatments are often best applied in late summer when the grubs are small and near the surface.

Correcting Watering Problems

St. Augustine grass needs about 1 inch of water per week, including rainfall.

Use a rain gauge or empty tuna can to measure how much water your sprinklers deliver.
Water until the soil is moist 4-6 inches deep. You can check this by pushing a screwdriver into the soil; it should slide in easily when the soil is properly watered.
If you have overwatering and soggy soil, you may need to improve drainage or simply adjust your irrigation schedule.

Fixing Soil and Mowing Issues

Compacted soil needs aeration. Rent a core aerator to pull small plugs of soil from your lawn. This creates channels for air, water, and nutrients. The best time to aerate is during the growing season, so the grass can recover quickly.

For mowing, always keep your St. Augustine at its recommended height of 3.5 to 4 inches. Never cut more than one-third of the grass blade at a time. And sharpen your mower blades at least twice a season. A clean cut heals faster and loses less water, keeping your grass greener.

Prevention is the Best Cure

A healthy lawn is your best defense against brown spots. Follow these practices to keep your St. Augustine strong:

Fertilize Properly: Use a slow-release fertilizer formulated for St. Augustine grass. Apply it according to schedule, typically in spring and early fall. To much fertilizer can cause more problems than it solves.
Maintain Good Thatch Control: A thin layer of thatch is normal, but if it gets over half an inch thick, it harbors pests and blocks water. Dethatch if needed.
Choose Resistant Varieties: If you’re planting new sod, consider varieties like ‘Palmetto’ or ‘CitraBlue’ that show better resistance to certain diseases and bugs.
Monitor Regularly: Catching a problem early makes treatment easier and more effective. Walk your lawn weekly to spot any changes.

FAQ Section

Q: What does fungus on St Augustine grass look like?
A: It depends on the disease. Brown Patch often shows as circular brown patches with a grayish “smoke ring” border. Gray Leaf Spot causes small, brown spots on blades that become elongated with gray centers. Take-All Root Rot causes yellowing that turns brown, and the roots will be dark and rotten.

Q: How do I know if I have chinch bugs or a fungus?
A: The float test described earlier is the best way to check for chinch bugs. Fungal diseases usually show specific patterns or markings on the grass blades themselves. If you see no bugs with the float test and the grass is rooted firmly, fungus is likely.

Q: Can brown St Augustine grass come back?
A> Yes, absolutely. If the brown is due to dormancy from drought or cold, it will green up when conditions improve. If the damage is from pests or disease but the roots and stolons (runners) are still healthy, it can fill back in. However, if the roots are killed, you may need to replace the sod in those spots.

Q: When should I apply fungicide to my lawn?
A: Apply fungicide at the first sign of disease, usually during warm, humid weather. Prevention applications can be made if you’ve had problems in previous years, starting before the typical disease season. Always follow the product label for timing and repeat applications.

Q: Are brown spots from dog urine treatable?
A: Yes. The best treatment is to flush the area with water as soon as possible to dilute the nitrogen. You can also train your dog to use a specific gravel area. For existing spots, you may need to reseed or resod if the grass is completely dead.

Dealing with brown spots on St. Augustine grass requires patience and the right action. Start with a careful diagnosis, then choose your treatment based on the cause. By combining the correct solution with good ongoing lawn care practices, you can restore your lawn’s health and prevent most future outbreaks. Remember, a consistent care routine is the key to a thick, green, and resilient St. Augustine lawn that can better resist problems before they start.