St. Augustine grass is a popular choice for lawns in warm, humid climates, valued for its dense, carpet-like growth and heat tolerance. Maintaining its vibrant green color can be challenging, as this grass is sensitive to environmental changes and maintenance practices. When St. Augustine turf turns brown, it signals that the grass is under significant stress and requires attention. Browning is a symptom, not a cause, and diagnosing the underlying issue is the first step toward restoration.
Understanding Cultural Stressors
Many problems that cause browning are directly related to common lawn care practices, often making them the easiest issues for a homeowner to correct. Improper watering is a frequent culprit, as St. Augustine grass thrives best when irrigated deeply but infrequently. Shallow, daily watering encourages weak, shallow roots, leaving the grass vulnerable to drought stress and browning. Conversely, excessive watering saturates the soil, which leads to root rot and other fungal diseases.
Mowing errors also significantly contribute to turf stress, particularly the common mistake of “scalping” the lawn by cutting the grass blades too short. St. Augustine grass should be maintained at a height of 3 to 4 inches. Removing more than one-third of the blade length shocks the plant and removes too much photosynthetic surface, exposing vulnerable stolons and the soil to direct sun. This exposure can quickly cause browning and weaken the root system. Soil compaction, caused by heavy foot traffic or equipment usage, restricts the necessary exchange of air and water needed for healthy root growth and nutrient uptake.
The Impact of Chinch Bugs
The Southern Chinch Bug is one of the most destructive insect pests for St. Augustine grass, causing rapidly spreading brown patches often mistaken for drought damage. These tiny insects (about 1/6 to 1/5 of an inch long) suck sap from the base of the grass plant. As they feed, chinch bugs inject a toxic substance into the plant tissue, which prevents water movement. This causes the grass blades to yellow, turn brown, and eventually die.
Damage typically begins in the hottest, sunniest, and driest areas of the lawn, such as those along sidewalks and driveways, and appears as irregular, expanding patches of dead grass. To identify the pest, perform a simple flotation test: remove the top and bottom of a coffee can, push it into the soil at the edge of a damaged area, and fill it with water. If chinch bugs are present, they will float to the surface within a few minutes, confirming the need for prompt treatment with an insecticide. Ignoring this pest can lead to the rapid death of large sections of turf.
Identifying Fungal Diseases
St. Augustine grass is susceptible to fungal pathogens that thrive under conditions of high moisture, humidity, and poor air circulation. One of the most common is Brown Patch (also known as Large Patch), which typically affects the grass during the cooler, wetter periods of spring and fall. This disease creates circular or semi-circular patches of discolored grass, often with a yellow outer ring. The distinguishing feature is that leaf blades in the affected area pull easily from the runner, revealing a rotten, dark brown or black sheath at the base.
Gray Leaf Spot is another prevalent fungal issue, primarily occurring during the hot, humid weather of mid-summer and early fall, especially following heavy rain or excessive nitrogen application. This disease is identifiable by the small, distinct lesions on the grass blades. These spots are typically diamond-shaped, gray-brown in color, and have a dark purple or brown border. While fungicide treatments are available, adjusting cultural practices, such as watering only in the early morning, is the preferred initial strategy to reduce the moisture necessary for fungal growth.
Issues Related to Soil Chemistry
Soil chemistry directly influences the grass’s ability to take up nutrients; an imbalance can lead to discoloration resembling browning. Iron Chlorosis is a common nutrient deficiency, especially in alkaline soils with a high pH, where iron becomes chemically unavailable. The grass blades first turn yellow, progressing to light brown, but the veins may remain green. This classic symptom distinguishes it from other issues.
Chemical burn is another cause of rapid, localized browning stemming from improper application of lawn products. Over-application of fertilizer, especially those high in nitrogen, or incorrect use of herbicides or pesticides can cause the grass tissue to dehydrate quickly. This damage appears as scorched, dead spots or streaks where concentrated chemicals made contact, leading to acute browning of the foliage. A professional soil test is the most reliable way to diagnose deficiencies or pH imbalances, providing the data to apply the correct amendments and restore the grass’s green color.