why is my st augustine grass turning yellow

Why is My St Augustine Grass Turning Yellow? (5 Problems and Solutions!)

St.Augustine grass makes up for a beautiful lawn with dark green coloration. The grass blades are flat and broad. The grass spreads via aboveground stolons called runners.

It grows natively in the south-eastern US, Mexico, Texas, Central and South America. It is loved by many lawn keepers for its elegance.

People that have St.Augustine lawns run into problems sometimes. They all mail me complaining that their lawn is yellowing.

St Augustine grass yellow streaks and spots

Do you see yellow spots on the blades of your St.Augustine grass? Your lawn is probably suffering from a disorder.

This is most likely due to Iron Chlorosis. You’ll see yellow-colored streaks and spots on the blades of St.Augustine.

This happens when the soil lacks Iron. This disorder is usually seen in the summer months as the grass couldn’t absorb iron as rapidly as it grows.

Iron supplement for St.Augustine grass

You need to give your lawn some Iron in a form the lawn can absorb easily. Iron Chelate and Iron sulfate work wonders on your lawn!

Chelated iron works the best but it’s quite expensive. Iron sulfate is a good alternative as it works well for the purpose.

Iron sulfate

Iron sulfate not only directly adds Iron to the soil but also helps release the Iron already present in the soil as it’s acid-forming.

The best way to fix the Iron deficiency in your soil is by adding Iron sulfate/Iron supplements throughout the year. Adding it once off doesn’t give desired results.


Add acid-forming fertilizers with Iron content to the soil once every 2-3 months. Do this throughout the year and your lawn will be fine.

Milorganite works awesome. It is a slow-release fertilizer. If your lawn is of average size, you may use 5-10 bags of Milorganite for best results.

That is, you may want to use 50-100 pounds of Milorganite per 1000 sq. feet of the lawn.

St Augustine grass yellow in spring

Does your St.Augustine grass turn yellow in spring? You don’t want your beautiful lawn to become ugly. You wanna know the reason?

This happens due to rains. Rains leech out the Nitrogen from the soil. The grass turns yellow due to the lack of Nitrogen.

Sometimes rains cause waterlogged conditions in your lawn. Waterlogged soil prevents the absorption of the essential nutrients by St.Augustine grass.

If you didn’t apply any Nitrogen fertilizer recently, apply some in August. This helps revive the Nitrogen-deficient soil.

Note: If the yellow grass turns brown it is an indication of a fungal infection. Apply fungicide to treat the grass.

St Augustine grass yellow circles

A variety of fungi affect St.Augustine grass. A fungal infection is characterized by yellow circles on grass blades. Such diseases are usually seen only in a part of the lawn.

Take-all root rot is caused by a fungal infection. This disease is triggered by excess rains and overfertilizing.

You’ll need to spray a fungicide on the infected areas of the lawn. The best time to apply this fungicide is in the spring and fall.

Myclobutanil and Azoxystrobin work wonders on Take-all root rot. Mix 1/2 ounce of water in 4 gallons of water and apply this mixture on 1000 sq. ft of lawn.

Apply this fungicide mixture to your lawn on a windless day. Two applications 28 days apart would suffice. Spray in spring and fall.

St Augustine grass turning yellow in summer

St.Augustine lawns experience Chlorosis in summer. The lawn may yellow because of this disorder which arises due to lack of Chlorophyll.

High temperatures deter the grass from absorbing the essential nutrients like Nitrogen and Iron which translates to Chlorosis.

You can add some organic matter to bring down pH and increase nutrient absorption by the grass. I advise you to add a layer of acidified compost, then add liquid seaweed with iron.

St Augustine grass yellow after fertilizing?

Did your St.Augustine lawn turn yellow after you fed it recently? This is a sign of overfertilizing. Too much fertilizer causes harm too.

Excess nitrogen salts in the fertilizer burn the grass blades. This is called leaf scorch. The grass yellows at the bottom and turns brown at the top.

This happens only with quick-release fertilizers. That’s why it’s better to use slow-release fertilizers like Milorganite.

To fix:

  • If you’ve noticed scorch early, you can fix it easily. Water the lawn thoroughly. Watering the affected areas washes away excess salts present in the soil.
  • Rake and Till the affected area.
  • Resod your lawn if a large part of the lawn is affected.

Chinch Bugs

Chinch bugs are a common pest of St.Augustine grass. Patches of dead grass surrounded by a circlet of yellow grass is a sign of Chinch bug infestation.

What causes Chinch Bugs?

If there’s a layer of thatch in your lawn, the lawn is more susceptible to a Chinch bug infestation. Thatch is just dead organic material.

Use a turf aerator to punch holes into the lawn and increase air movement in the lawn. This helps prevent a Chinch bug infestation.

There is a cultivar of St.Augustine grass that is resistant to Chinch bug infestation called ‘Captiva’. This cultivar is hardy in US Zones 8b-11.

Does Triazicide kill Chinch Bugs?

Spot spraying the affected areas with Triazicide would work effectively. Inspect the affected area every 3-5 days to make sure the treatment is working.