Why is my St. Augustine grass dying? Common diseases and how to identify and remedy.

The horror for any proud homeowner, who takes pride in the appearance of their lawn, is waking up to a once vibrant, healthy green view now speckled with imperfections, or worse, near-annihilation of the entire turf. This hardship is especially true for owners with St. Augustine grass as it is a very sensitive turf grass.

But don’t throw in the towel yet! Although, you should probably roll up the water hose. (Hint, hint).

We will cover the top St. Augustine diseases, and what you should know about how to identify them, and the course of action to remedy them.

Brown Patch

First, the most common lawn disease is Brown Patch – a soil borne fungal disease caused by different strains of the Rhizoctonia solani fungus, and is unlimited to the different turf grass it can affect. Thankfully, Brown Patch is an ascetic-only disease and will not kill the turf. But how does the fungus infect the lawn? For most fungal diseases, the answer is a combination of human error and favorable growing conditions.

The pathogen lives dormant in the soil and survives the winter underneath thick thatches until the weather becomes warmer and wet. Even though the peak growth activity occurs at temperatures of 70º–85ºF with high humidity levels, the disease will start to show growth once the night air temperature reaches between 40º – 70ºF when the humidity levels begin to rise and the presence of a nearby susceptible host. The optimum conditions trigger the fungus to advance to the next stage in its life cycle – spore development and infection. The pathogen infects leaf tissues nearest the soil. Conditions which weaken the turf such as mowing with dull blades, mowing below the recommended height and improper watering practices. Just like us, diseases jump at the opportunity of a free meal.

So what are the signs and symptoms?

As the name implies, Brown Patch appear in irregular circular areas of brown and diseased turf often surrounded by a narrow, dark brown or gray ring called a “smoke ring” which is evidence of active fungal growth.  The interior may display a healthier green color. Patch size can range from a few inches to several feet in diameter. As a self-diagnosis, pull blades of grass at the edge of the infected area. If the leaf blades can be extracted easily from the stems and appear brown and rotted at the base of the blades, it’s an indication that you have Brown Patch and should be treated quickly to stop the disease from spreading.

Remedies and disease management of Brown Patch include:

  • Fungicide. While it is effective, it is also the most expensive option. Because the fungicides available for Brown Patch are only effective for 30 days, at least 2-3 treatments must be made to manage the disease. However, fungicide cannot repair the damage done by the fungus; they can only prevent the occurrence or spread of it. Therefore, the course of action is the opposite of insecticides where we go guns a’blazing with a kill-it-with-fire approach. (Not literally..) Fungicides should be applied when the opportunity for disease is on the horizon, in other words, before spore development. Applications in 30-day intervals beginning September 1 and ending when the night temperatures reaches 40ºF is the ideal time frame. That being said, per our licenses, pesticides can only be applied when there is a target pest.  Not all turf grass varieties or properties contract the disease, therefore we cannot treat every property for Brown Patch. In other words, we can only treat a problem when we have a problem. We must be environmentally responsible.
  • Proper mowing etiquette. Keeping the turf height at the recommended level and sharp mower blades are the first line of defense. Do not mow wet grass. Not only will it create ruts in the ground, stain clothing, and clog mowers, both man and machine will become disease carriers.
  • Pruning of surrounding trees and shrubs in the infected areas will help to dry excess moisture caused by excessive shading.
  • Improve turf grass root system. Good soil drainage and core aeration reduces soil compaction and thatch accumulation to increase soil porosity.
  • Avoid spreading the disease. Do not walk through infected areas when it is wet, nor allow pets to roam through the wet grass. And again, do not mow wet grass.
  • Avoid over-watering. Remember that hint? Fungus thrives in excess moisture. Eliminate watering in the evenings and limit to watering in the early morning hours so the grass will have time to dry out during the day.

St. Augustine Decline (SAD)

Next on the list is St. Augustine Decline – a viral lawn disease caused by the Panicum mosaic virus. Yep, turf grass are susceptible to viruses too. The virus can live for years in plant debris and moves around the environment by wind, rain, contaminated equipment, or installation of already infected sod. Because the pathogen cannot create its own wound on the host plant, it invades the turf grass through mechanical wounds such as mowing and plowing. Once a yard is infected, the disease can only be transmitted through mowing, edging or other mechanical methods.

The symptoms of the virus are quicker to exhibit in warmer temperatures around 84 to 95ºF as the incubation period can take as few as 7-18 days during this time. The symptoms include:

  • Strippling of leaf blades. Known as chlorotic mottling and may go unnoticed or associated with mite damage.
  • Yellow-ish spotted blades. Also called chlorosis, this is a sign of stress caused by the virus. Mite damage can also cause chlorosis, but if the discoloration is uniform over the entire lawn, it is an indication of nutrient deficiency which is a sign of St. Augustine Decline.

Affected turfs may begin to thin and allow for establishment of weeds to take place.

Unfortunately, there is no cure for the affected grass other than to let it eventually die. In some cases, it may be necessary to remove and replace the infected turf. However, with proper management control, nutrients can be applied to promote new healthy growth and provide resistance to future outbreaks.

Gray Leaf Spot

Gray Leaf Spot is a fungal lawn disease caused by the Pyricularia grisea fungus. It can produce large amounts of infectious spores in a very short period of time causing evident decline in symptomatic tissue. Germination occurs within a few hours after contact with a susceptible host with symptoms appearing within hours of infection. Mowed leaf tips provide the best invasion to the leaf tissue, keep blades sharp! The pathogen kills the plant from severe leaf blight and symptoms develop rapidly with warm temperatures above 80ºF, high humidity, and prolonged moisture.

Symptoms may rapidly change, first exhibiting tiny lesions, which often go unnoticed, before enlarging to round, brown to ash-colored spots measuring 2-5 cm in diameter and can grow up to 40 cm in diameters. Thinning of grass blades may occur. In later stage development, the discoloration may turn purple to brown with a more oval shaped spot. Severe outbreaks of the disease may cause the turf grass to appear burned or scorched.

Treatments for Gray Leaf Spot includes:

  • Fungicide Treatment
  • Avoid over-watering. Over-watering is a major factor in creating a favorable condition for disease development. Reduce excessive leaf wetness and soil compaction to alleviate stress to the yard.
  • Mowing practices. Mow with sharp blades and at the proper height. St. Augustine should be mowed between 3-4 inches.

Take All Patch

Take All Patch is a root rot fungal disease caused by the Gaeumannoymyces graminis var. graminis fungus that lives in the soil with thatches and decaying plant matter in winter dormancy. It spreads mainly through roots and stolons by runner hyphae. The disease is more likely to be transmitted when infected grass, thatch, or soil is moved elsewhere, rather than by mowers or foot traffic.

Symptoms often appear in spring or early summer when the turf emerges from winter dormancy. Early symptoms exhibit chlorosis that eventually turn brown and wilted and thinning turf in irregular patches. The disease is commonly misdiagnosed as Brown Patch disease due to similar early symptoms. Take All Patch can be seen as a “reverse Brown Patch” because instead of an outer dark ring, the disease affects the roots and thinning of the blades reveal the soil patches spanning from 1 foot to more than 20 feet in diameter.

Stolon death follows after grass blades have become brown and wilted, and can easily be extracted from the soil due to poor root system. The key difference between identifying between Brown Patch and Take All Patch is that the stolons in Brown Patch remains green to allow recovery in the spring, while Take All Patch stolons are short, blackened, and rotten.

Remedies and prevention include:

  • Fungicide
  • Avoid over-watering
  • Encourage healthy root system. Low areas that hold water are more susceptible to disease due to all the excess moisture. Good soil drainage and core aeration reduces soil compaction and thatch accumulation to increase soil porosity.
  • Mowing practices. Mow with sharp blades and at the proper height. St. Augustine should be mowed between 3-4 inches.

As you can see, fungal diseases have a common set of remedies and prevention methods: fungicide, avoid over-watering, and core aeration for healthy root systems plus correct mowing practices. Applying these lawn management techniques can help prevent susceptibility to many diseases.

If your lawn is suffering from any of these conditions or other mishaps, give our turf professionals a call for correct diagnosis and proper course of action for treatment!