Zoysia grass is a popular warm-season turf known for its dense, carpet-like texture and resilience in heat, but its vibrant green color can quickly turn brown when under stress. This discoloration signals that a specific environmental factor, maintenance error, or biological threat is affecting the lawn’s health. Diagnosing the cause is crucial, as the proper solution for one issue, such as drought, can worsen another, like a fungal infection.
The Natural Cycle of Zoysia Dormancy
Zoysia is a warm-season grass that thrives during the summer but enters a protective state known as dormancy when temperatures fall consistently. When soil temperatures drop below approximately 55°F, the grass ceases active growth and turns a uniform straw-brown or tan color. This golden-brown appearance is a natural survival mechanism, not a sign that the grass is dead.
The entire lawn usually assumes this consistent color, which helps distinguish seasonal dormancy from localized stress or disease. The roots and crowns remain alive and healthy below the soil surface, ready to green up again when warmer weather returns. A simple tug test can confirm dormancy; if the blades resist pulling up and the roots hold firm, the grass is merely resting.
Browning Due to Water Stress
Water imbalance is a frequent cause of browning, as both too little and too much moisture lead to similar visual outcomes through different processes. Drought stress first causes the grass to lose turgidity, resulting in a distinct gray-blue tint before the blades turn brown. When the soil is too dry, Zoysia blades often curl inward to conserve moisture, and footprints remain visible because the turf lacks the water pressure to spring back immediately.
Conversely, overwatering and poor drainage cause browning by suffocating the root system. Prolonged saturation inhibits the grass’s ability to absorb nutrients and water, leading to root decay. This excessive moisture also creates a prime environment for fungal growth and can cause the grass to turn yellow before browning entirely.
Identifying Pests and Disease Damage
Fungal diseases and insect pests can cause distinct patterns of browning that often appear as localized patches. Zoysia Patch, caused by the fungus Rhizoctonia solani, is a common disease appearing as circular or semi-circular patches of discolored turf. These patches are most noticeable during cool, wet periods in the spring and fall when Zoysia growth is slow. The outer border may have a darker, water-soaked appearance or an orange-to-yellow ring of actively infected grass blades.
Insect damage presents different visual cues, with chinch bugs causing irregular, spreading patches of straw-like browning, often in the hottest, driest areas of the lawn. These pests feed by sucking the fluids out of the grass blades, which prevents water from reaching the leaf tips. Grub damage, caused by the larvae of various beetles, is identified by patches of turf that can be easily rolled back like a carpet because the grubs have eaten the root system.
Cultural Causes (Mowing and Nutrient Issues)
Browning can result from improper maintenance practices or chemical stress. Zoysia grass is typically maintained at a low height between 1 to 2.5 inches, but cutting the turf too short at once causes scalping. Scalping removes too much green leaf tissue, exposing the sensitive brown stem crown and reducing the plant’s capacity for photosynthesis.
A related issue is the violation of the “one-third rule,” which states that no more than one-third of the grass blade’s total height should be removed in a single mowing. Ignoring this rule, especially during the active growing season, causes immediate stress and widespread browning as the plant struggles to recover.
Fertilizer burn is a chemical stress that occurs when too much nitrogen fertilizer is applied, or it is applied unevenly, causing the grass to rapidly dehydrate. The high salt concentration in the fertilizer draws water out of the grass roots, resulting in streaks or scorched patches of crispy, brown turf.