St. Augustine grass (Stenotaphrum secundatum) is a popular warm-season turfgrass known for its thick, carpet-like texture and deep green color, especially in the southern United States. Homeowners often choose this variety for its shade tolerance and ability to establish a dense lawn. When this grass begins to fail, displaying patchiness, thinning, or widespread browning, it signals a significant underlying problem that requires immediate diagnosis and a targeted revival plan. This guide provides a direct approach to identifying the specific causes of decline and applying the necessary treatments to restore turf health.
Identifying the Causes of Decline
Effective revival starts with accurate diagnosis. One of the most common biological threats is the chinch bug, a tiny insect that feeds on the grass stems and injects a toxin preventing the plant from transporting water. Chinch bug damage typically appears as irregular, expanding yellow and brown patches, often starting in the hottest, driest areas of the lawn near sidewalks or driveways.
Another significant issue is Brown Patch, a fungal disease caused by Rhizoctonia solani, which usually manifests in the cooler, wetter conditions of spring and fall. Brown Patch forms characteristic circular or semi-circular rings of brown turf. The grass blades easily pull away from the runner because the fungus has rotted the stem base.
Beyond pests and disease, environmental stressors play a large role in St. Augustine grass decline. While it is more shade-tolerant than many other warm-season grasses, inadequate sunlight will cause the turf to thin out over time. Poor watering habits, such as light, frequent irrigation, encourage shallow root growth, making the turf vulnerable to heat stress and disease.
Adjusting Cultural Practices for Immediate Revival
Correcting basic maintenance practices is the fastest way to stabilize the distressed turf and encourage new growth without relying on chemical inputs. St. Augustine grass performs best when mowed at a height between 3.5 and 4 inches. This protects the stolons (runners) and maximizes the leaf surface area for photosynthesis. Mowing below this height places stress on the grass, causing it to thin and become susceptible to weed invasion.
Proper watering involves a “deep and infrequent” schedule, aiming to deliver about one inch of water per week, either through irrigation or rainfall. Applying water for longer periods, but less often, encourages the roots to grow deeper into the soil, improving drought tolerance and overall plant resilience. Watering should be done in the early morning hours, allowing the grass blades to dry completely before nightfall, which reduces conditions favorable for fungal growth.
Relieving soil compaction is another physical adjustment that improves turf health, as compacted soil restricts the movement of air, water, and nutrients to the root zone. Light core aeration, which removes small plugs of soil, is the most effective method to alleviate this compaction and should be performed when the grass is actively growing. Removing excessive thatch buildup, a layer of dead organic matter, is also helpful because thick thatch can harbor pests and block water penetration.
Nutrient Management and Targeted Treatment
Once cultural practices are optimized, the next step involves targeted nutritional support and specific chemical treatments. St. Augustine grass is a high-nitrogen-demand turf, but the nutrient should be supplied using a slow-release fertilizer to provide consistent feeding without causing excessive, disease-prone growth. A typical fertilization schedule involves applications during the active growing season, from spring through early summer, with an annual total of 3 to 5 pounds of nitrogen per 1,000 square feet.
Yellowing of the grass blades, known as chlorosis, is common and often indicates an iron deficiency, especially in high-pH soils. Applying chelated iron supplements, either as a foliar spray or granular product, will enhance the deep green color by aiding chlorophyll production without stimulating the rapid vertical growth caused by nitrogen. A soil test is recommended to determine the precise nutrient needs and to check the soil pH, which ideally should be between 6.0 and 7.5.
For diagnosed pest issues, such as chinch bugs, targeted application of a systemic insecticide is necessary, as these pests feed by sucking fluids from the grass plant. Neonicotinoid-based products are often recommended for effective control. If Brown Patch was identified, a granular or liquid fungicide containing active ingredients like propiconazole or azoxystrobin should be applied to the affected area and a surrounding border to halt the spread of the fungus.
Long-Term Maintenance for Sustained Health
Maintaining the health of revived St. Augustine grass requires consistent attention to prevent future decline. This involves monitoring for pest activity monthly throughout the summer, particularly in areas prone to heat and drought stress. Trimming overhanging trees and shrubs regularly will ensure sufficient sunlight reaches the turf, preventing thinning and vulnerability to shade-related decline.
A healthy turf naturally resists weed invasion, but pre-emergent herbicides are effective for preventing annual weeds from germinating. For St. Augustine grass, select herbicides that are safe for the species, such as those containing Atrazine, and apply them when soil temperatures reach the appropriate threshold in spring and fall. Following a consistent fertilization calendar, 2 to 3 times per year during the growing season, provides the steady nutrition required for a dense, resilient lawn.