The most common reason St. Augustine grass turns yellow is chlorosis, a condition caused by a lack of chlorophyll due to nitrogen or iron deficiency.
Other causes of yellowing St. Augustine grass are root rot, chinch bugs, chemicals, overwatering, too much fertilizer, disease and dog urine.
Why is my St. Augustine turning yellow?
Chlorosis
Chlorosis is one of the most common reasons your St. Augustine might turn yellow. This happens during the hot summer. Chlorosis occurs when there is a lack of chlorophyll caused by a deficiency of iron or nitrogen. When the temperature and the soil pH are high, the grass cannot effectively absorb nutrients from the soil. Poor soil health and compaction can also add to the problem.
You can help the grass by feeding the soil to stimulate microbial growth. This will help the grass absorb the nutrients it needs, even if the temperature is hot. You can also add mulch or compost to the soil to make it more acidic.
You can aerate the soil to reduce any compaction and to boost microbial activity. These microbes help break down organic matter and make nutrients available to your plants.
Root rot
Root rot is caused by a fungus that causes the grass to turn yellow. It can also cause the grass to thin out and die if it is not controlled or treated in time.
You can tell that your St. Augustine has root rot if you see yellow rings around the grass during the spring or summer.
Avoid thinning and yellowing in your grass by using a fertilizer that has ammonium nitrogen. You can also use a fungicide that contains azoxystrobin. Mix half an ounce of the fertilizer with five gallons of water to cover 1,000 square feet of grass. Spray the mixture on the grass once a month. Make sure you wear protective clothing while handling the fertilizer.
Chinch bugs
When you see patches of dead grass encircled by yellowing grass, it might be due to a chinch bug infestation. These insects are very common St. Augustine pests. They like to attack the grass when it has a lot of thatch and is susceptible to parasites.
You can prevent chinch bugs by mowing the grass to remove the thatches. You can then apply chinch bug spray to get rid of the insects.
Chemicals
Accidentally spraying or spilling chemicals on your grass can also result in yellow spots. You can remedy this immediately by flooding the affected area with water and covering the grass with an absorbent material, like a towel. Also remember that insecticides and herbicides contain chemicals that can scorch your lawn if used extensively.
Overwatering
If you overwater your grass it can lead to poor root development. Excessive water can deplete the soil of oxygen because it is waterlogged. The grass will end up with shallow and underdeveloped roots that will not effectively take up nutrients, water or oxygen. This will result in the grass turning yellow.
Overwatering also makes your grass more susceptible to fungal diseases and pests, and can cause the grass to thin out and discolor.
You can avoid overwatering your grass by adjusting your watering schedule. Only water the lawn if the top two inches of soil are dry. If you water your lawn three times a week and notice yellow spots, try reducing the frequency and only water it twice a week.
Too much fertilizer
If you give your grass too much fertilizer, you can end up burning it, especially if you use synthetic fertilizer. If you have just recently applied fertilizer on your grass and it started to turn yellow, then it is most probably due to the fertilizer. Too much nitrogen salts found in synthetic fertilizer can burn the leaves on your St. Augustine. Other signs of overfertilization include fertilizer crust on the surface of the soil, grass growing slowly, grass blades turning brown and yellowing of the grass starting from its base.
Disease
Some of the diseases that affect St. Augustine grass can cause yellow or brown patches. Common diseases include lawn fungus and dollar spot.
You can treat lawn diseases by using a fungicide. You can also treat your lawn immediately after winter to kill any fungi that develop during the frost.
Dog urine
Dog urine has high nitrogen compounds, so it is no surprise that it can be harmful to your grass. If you have a dog and you see yellow spots on your grass, it is likely that they are due to the dog’s urine.
You can prevent dog urine spots by washing off the urine with a hose after your dog has gone to the bathroom. You can also use a dog urine neutralizer, or train your dog only to pee in certain parts of your yard where it will not be as noticeable as on your green lawn.
Use
When your grass has just been installed or planted, make sure you put up some rope to warn people not to step on it. Give the grass enough time to develop a root system and become healthy before letting people or animals walk over it. Even if the grass is established, try to limit the use and wear on the grass. This will keep the grass green and lush.
Conclusion
Yellowing St. Augustine grass is most probably due to chlorosis. Chlorosis is a condition in which the grass lacks chlorophyll because its nutrient uptake has been impaired, leading to the yellowing of the grass blades. Other notable causes of yellowing St. Augustine are root rot, chinch bugs, chemicals, overwatering, too much fertilizer, disease, dog urine, and too much use.
Image: istockphoto.com / Ruth Peterkin