7 Reasons St Augustine Grass Is Turning Yellow | How to Fix

St. Augustine is an incredibly popular grass species throughout the southern United States and similar climates. It’s regarded as the most shade-tolerant of warm-season grasses and, once established, spreads vigorously.

While St. Augustine is sometimes labeled as high-maintenance, its lush appearance makes it well worth any extra effort. Unfortunately, it is also prone to yellowing when damaged.

Below you’ll find 7 of the most common reasons why your St Augustine grass is turning yellow, as well as basic steps you can take to revive it.

Tell Tale Signs St Augustine Grass Is Yellowing

There are many common symptoms associated with yellow grass. As you examine your lawn and work to identify the root cause of its discoloration, keep an eye out for these additional signs of damage:

  • Wilting
  • Faded color
  • Thin patches
  • Dryness
  • Insect activity
  • Fungal spores or threads

Can Yellow St. Augustine Grass Recover

Grass blades that have already turned yellow generally won’t regain their original color. However, new, green blades will emerge in their place as long as the root system underneath the soil continues to thrive.

The only time you’ll see yellow grass fail to recover is when the root system itself has died. This can occur in patches or, in extreme cases, throughout the entire lawn. Since St. Augustine is a spreading grass, small bare patches should naturally fill in with time. 

St Augustine Grass Is Turning Yellow

7 Reasons St Augustine Grass Is Turning Yellow

When St. Augustine’s grass turns yellow, it’s a clear sign that something is wrong with the environment. If you want to get your lawn on the road to recovery, however, you must first diagnose the exact cause of its discoloration.

Take note that many cases of yellow turf grass appear very similar to each other. It certainly doesn’t hurt to get a professional’s second opinion before moving forward with a treatment plan.

1. Iron Deficiency 

In my experience, one of the most common causes of yellow turf grass is iron deficiency. St. Augustine lawns are no exception.

Iron is a vital micronutrient that plants utilize during chlorophyll synthesis. Without adequate iron, your lawn is incapable of creating the chemical that gives it its green color. 

The tricky thing about an iron deficiency diagnosis is that it doesn’t necessarily mean your soil is low in iron. In many cases, iron deficiencies are actually caused by excess phosphorus or an elevated pH level. Both of these factors impact how easily plant roots can absorb available iron molecules within the soil.

Symptoms

A keen eye can distinguish iron chlorosis — the technical term for an iron deficiency — from other causes of yellow grass. 

St. Augustine lacking iron typically develops yellow stripes between the blades’ veins. You may need to look closely to see this striation.

As the condition worsens, the grass blades may turn completely yellow or even white. Iron chlorosis may affect your entire lawn at one time or appear in isolated patches.

Iron chlorosis typically affects new grass growth first. Keep this in mind when monitoring your lawn for developing symptoms.

How To Fix

I recommend conducting a soil test any time a nutritional deficiency is suspected as the cause of discoloration. For the best results, invest in a test that also identifies soil pH.

Avoid the use of phosphorus fertilizers unless advised by a soil analysis.

Iron can be directly applied to grass via a foliar spray. If you decide to add iron to the soil, I highly recommend selecting a chelated iron product. Chelated iron is more readily available to grassroots than other forms of the nutrient.

2. Nitrogen Deficiency

Another nutritional cause of yellow St. Augustine grass is insufficient nitrogen. Nitrogen is the most important nutrient for plant health and, like iron, is essential to chlorophyll production.

Symptoms

A lack of nitrogen in the soil will quickly manifest as grass blade discoloration. You may notice your lawn fade to lime-green before it fully turns yellow.

Nitrogen deficiencies are extremely easy to mistake for iron chlorosis. Two signs that you’re dealing with a lack of nitrogen versus iron include:

  • Discoloration that covers the entire grass blade (not just interveinal stripes)
  • Yellowing that affects old growth first

Visual symptoms like these are just one step in diagnosing your lawn’s ailment. A soil test is always the best way to identify nutritional problems.

How To Fix

You can address nitrogen deficiencies by applying fertilizer for greener grass such as a high-quality lawn fertilizer for St. Augustine grass.

3. Fertilizer Burn or Scorch

Excess fertilizer can also have a negative effect on turf grass. Often, nitrogen is the specific nutrient to blame.

Nitrogen damage is not always a direct result of fertilizer use. Another common cause of nitrogen burn on lawns is dog urine. Animal urine contains concentrated nitrates that can cause nearly identical damage to grass as excess fertilizer.

Symptoms

Overfertilized grass generally appears dry and can even feel more coarse to the touch. The grass will also turn yellow or brown and may wilt.

Fertilizer burn often occurs immediately after fertilizer applications. It may occur in patches or affect the entire lawn depending on the exact source.

In cases of severe fertilizer damage, sections of lawn may rapidly die off.

How To Fix

You can flush excess nitrogen from the soil by watering the area heavily. This will help push nutrients further into the soil away from your lawn’s roots. The same strategy can be used to flush out animal urine causing lawn damage.

Prevent future fertilizer burns by testing your soil and measuring all fertilizer applications carefully.

Do not fertilize when St. Augustine is dormant. You should only apply lawn fertilizers when the grass is actively growing.

4. High Temperatures

St. Augustine is a warm-season grass that tolerates high temperatures with relative ease. But it still has its limits.

St. Augustine typically thrives in temperatures between 80 and 100°F. Temperatures outside of this range can damage the grass.

Symptoms

Heat-stressed St. Augustine will generally look wilted before other symptoms appear. The overall color may fade to yellow or brown. 

I’ve noticed that heat damage usually affects the upper tips of grass blades first. You might also notice areas that receive prolonged sun throughout the day show more serious symptoms than those in sheltered areas.

How To Fix

Supplying adequate moisture during hot weather can offset heat damage. Keep an eye on the weather forecast and irrigate your lawn as needed to prevent drought stress.

Avoid applying fertilizers, herbicides, or pesticide treatments during heat waves. I also don’t recommend mowing your lawn when it is showing signs of heat stress.

5. Fungal Disease

Many fungal diseases impact the color of turf grass. The most notorious diseases found in St. Augustine lawns include brown batch fungus and take-all root rot (TARR). These infections are caused by Rhizoctonia solani and Gaeumannomyces graminis respectively.

Symptoms

Brown patch fungus is aptly named because it typically presents as large, brown patches of turf. The edges of these patches are often irregular and undefined. Cool or wet conditions are usually the main causes of fungus in lawns.  

Symptoms of TARR include patches of yellow grass, excessively dry turf that doesn’t recover with watering, and decayed roots. This disease often rears its ugly head in spring or early summer.

If you suspect TARR within your own lawn, you can pull up a clump of affected grass and examine the roots. Infected roots typically appear black and decayed, and won’t put up resistance when pulled from the soil.

How To Fix

Good lawn maintenance is the best preventative measure against fungal disease. Things like improper irrigation, nutrition, and poor soil quality will all increase the risk of infection.

Brown patch fungus can be controlled with a chemical fungicide like azoxystrobin, flutolanil, or pencycuron. According to the Texas Agrilife Extension Service, TARR responds to azoxystrobin, myclobutanil, propiconazole, and thiophanate-methyl.

6. Excessive Water

An oft-overlooked cause of yellowing grass is excess water in the soil. This could be caused by overzealous irrigation, heavy rainfall, or poor drainage. 

Many people don’t realize that grass takes up oxygen through its roots. If your lawn is waterlogged, the roots can essentially drown from a lack of oxygen.

Nitrogen deficiency can also be the result of overwatering. This is called nutrient leaching and occurs when heavy rain or irrigation flushes nutrients deep into the soil where grassroots can’t access them.

Symptoms

In addition to discoloration, monitor your lawn for signs of poor drainage. If the soil’s surface seems to remain wet for a long time after rain or irrigation, poor drainage is likely the issue. 

How To Fix

Research the exact water needs of your St. Augustine cultivar and keep track of how much water it receives from rain and irrigation. Try to water infrequently but deeply to promote healthy root development without oversaturating the soil.

Core aeration may improve drainage and increase the amount of oxygen your lawn has access to. Amending the soil with a layer of aged compost may also improve drainage.

7. Chinch Bugs

Chinch bugs are small insects that rely on turf grass as a primary food source. These pests pierce grass blades to access the moisture inside. When they do so, however, they cause damage that eventually turns the blade yellow.

Symptoms

Chinch bugs are most active between April and October. Chinch bug damage is most often seen in sunny areas near paved surfaces.

St. Augustine infested with chinch bugs will often appear heat- or drought-stressed. To confirm the presence of chinch bugs consider conducting a float test.

How To Fix

My preferred cultural control methods for chinch bugs include proper irrigation and regular thatch removal. These practices will prevent or minimize chinch bug damage to your lawn.

Severe infestations may require pesticide treatments. Bifenthrin is the most highly recommended active ingredient for chinch bug control.

St. Augustine Grass Turning Yellow: Solved

There are several reasons St. Augustine grass may turn yellow. While some are fairly mild and will resolve themselves in a matter of time, it’s best to identify the root cause of your lawn’s discoloration before things get serious.

Early diagnosis and management is the ideal way to prevent long-term damage to your St. Augustine turf. If you’re ever unsure about the exact cause of your lawn’s damage, I highly recommend reaching out to a professional for additional help.

Rest assured, with swift treatment and ongoing maintenance, yellowing St. Augustine grass is almost guaranteed to make a full recovery.