Zoysia grass is popular due to its dense, carpet-like texture and resilience in warm climates. Despite its hardiness, a common issue is the sudden appearance of yellow or off-color patches across the lawn. This discoloration signals that the grass is under stress, and identifying the specific source is the first step toward restoring its vibrant green appearance. Yellowing is rarely caused by a single factor, often requiring a careful look at environmental conditions, maintenance habits, soil health, or the presence of pests and disease.
Environmental Stress and Improper Mowing
Yellowing often relates directly to the lawn’s environment and physical management. Zoysia requires deep, infrequent watering to promote a robust root system, typically needing about one inch of water per week, delivered in a single session. Over-watering in poor-draining soil can suffocate the roots, creating an anaerobic environment that causes yellowing and encourages root rot. Conversely, insufficient watering during heat stress causes the grass blades to dehydrate, appearing straw-colored or yellow as they enter drought-induced dormancy.
Improper mowing, particularly “scalping,” is another common source of physical stress. Scalping occurs when the grass is cut too short, removing too much photosynthetic leaf tissue and exposing the lighter lower crown and stems. Zoysia is healthiest when maintained at a height between one and two inches. Mowing too low reduces the plant’s ability to produce energy, resulting in a stressed, yellowish appearance that requires time to recover.
As a warm-season species, Zoysia’s discoloration may also be a natural, seasonal process. When soil temperatures drop below 50 degrees Fahrenheit, the grass enters dormancy, turning a uniform tan or brown until warmer conditions return. Prolonged or severe drought during the active growing season can also force the grass into this protective state.
Identifying and Correcting Nutrient Imbalances
The chemistry of the soil plays a significant role in maintaining Zoysia’s deep green color. A lack of available nitrogen is a frequent culprit, presenting as a general, uniform yellowing, especially in older grass blades. Nitrogen is a component of the chlorophyll molecule, and a deficiency hinders the plant’s ability to photosynthesize. This issue is often corrected with an application of a slow-release, balanced nitrogen fertilizer to support consistent growth.
Micronutrient deficiencies can cause chlorosis, a distinct type of discoloration. Iron chlorosis, for example, appears as yellowing between the veins of new growth, while the veins remain green. This problem often results not from a lack of iron, but from the nutrient being chemically unavailable, which frequently occurs in soils with a high pH level. Applying a chelated iron supplement provides a quick, temporary fix, but the long-term solution requires addressing the underlying soil chemistry.
Zoysia grass prefers a soil pH that is slightly acidic to neutral, ideally within a range of 6.0 to 7.0. If the pH falls outside this range, the grass’s ability to absorb necessary nutrients like iron and manganese is inhibited. A professional soil test is the only reliable way to diagnose this issue, allowing for precise amendment with sulfur to lower an overly alkaline pH or lime to raise an overly acidic pH.
Biological Threats Pests and Fungi
Yellowing can be symptomatic of an attack from living organisms, including fungal pathogens and various insects. Fungal diseases thrive under specific environmental conditions, such as high humidity, poor air circulation, and extended periods of leaf wetness. Dollar Spot is a common fungal issue that manifests as small, circular, straw-colored patches, often linked to insufficient nitrogen or excessive thatch buildup. Rust, caused by the Puccinia genus, leaves an orange or yellowish, powdery residue on the grass blades that easily rubs off.
The most damaging insect pests cause yellowing by feeding on the root system or sucking fluids from the grass blades. White grubs, the larvae of various beetles, feed on the roots, preventing the grass from absorbing water and nutrients. A diagnostic sign of a grub infestation is the ability to pull up sections of the grass easily, like loose carpet. Pests such as chinch bugs extract plant fluids, causing irregular yellow or brown patches, typically starting in the hottest, sunniest areas.
Targeted treatment is necessary once a biological threat is confirmed. Fungal diseases often require adjustments to cultural practices, such as watering only in the early morning to allow blades to dry before nightfall, or the application of a specific fungicide. For grubs, treating the area with a curative insecticide or introducing beneficial nematodes can reduce the population and allow the damaged root system to recover.
Long-Term Recovery and Maintenance Strategy
Addressing the root cause of Zoysia yellowing requires a shift toward preventative, consistent maintenance. Establishing a routine of deep, infrequent irrigation strengthens the root system, making the grass more resilient to drought and disease. This practice trains the roots to grow deeper, enabling them to access moisture reserves in the subsoil.
Adherence to the recommended mowing height of 1 to 2 inches maximizes the grass blade’s capacity for photosynthesis and protects the crown. Annual soil testing is a foundational step, providing data to proactively correct pH imbalances or nutrient deficiencies before they trigger yellowing. Zoysia’s dense growth habit makes periodic aeration and dethatching necessary to prevent organic matter from suffocating the roots and creating a breeding ground for disease. Consistent observation and early detection allow for swift, targeted intervention.