Tall Fescue is a popular cool-season grass known for its deep green color and relatively good heat tolerance. Seeing your lawn turn brown is a common issue, especially as summer temperatures rise. Browning signals that the grass is under stress and struggling to cope with environmental demands or external threats. Diagnosing the exact cause of the discoloration is the first step toward recovery, as the culprit often falls into categories like lack of water, biological threats, or maintenance errors.
Browning Caused by Environmental Stress
Environmental conditions, primarily heat and drought, are the most frequent causes of browning in fescue lawns. Tall Fescue grows best in cooler temperatures and begins to struggle significantly when air temperatures consistently rise above 80°F. Prolonged exposure to high heat forces the plant to conserve moisture, leading to visual decline.
An early indicator of severe heat or drought stress is a shift in color to a bluish-gray or dark purplish-green hue, often accompanied by limp or curled leaf blades. If your footprints remain visible after walking across the lawn, the grass lacks the turgor pressure needed to spring back, confirming a serious need for water. This discoloration quickly progresses to a straw-brown color as the plant enters survival dormancy.
Improper watering exacerbates heat stress, especially when it is too shallow or too frequent. Brief watering encourages short, weak roots that cannot access deeper moisture. To mitigate this, irrigate deeply and infrequently, aiming for about one inch of water per week. Water in the early morning to minimize evaporation and reduce the time the grass blades remain wet, which helps prevent fungal issues.
Fungal Diseases and Insect Pests
When browning appears as distinct, localized patches rather than a uniform color change, the issue is often biological, involving fungus or insect activity. The primary disease threat to Tall Fescue in warm, humid conditions is Brown Patch. This fungus becomes highly active when temperatures are high, especially in saturated air conditions.
Brown Patch presents as roughly circular patches of thinned, brown grass that can range up to several feet in diameter. A distinctive diagnostic feature is a dark, purplish-green or “smoke ring” border where the fungus is actively spreading into healthy tissue. Unlike drought stress, which affects the whole lawn uniformly, Brown Patch leaves individual leaf blades with tan lesions surrounded by a dark brown border.
Insect pests, particularly white grubs, can also cause browning by damaging the root system. White grubs, the larvae of various beetles, feed on the roots, severing the connection to the soil. An infestation often results in irregular patches of brown turf that look and feel spongy. A simple tug test on the affected area will reveal the turf can be easily lifted or rolled back because the roots are gone.
Cultural Practices and Chemical Burns
Browning can also result from errors in routine lawn maintenance, commonly referred to as cultural practices. Mowing the grass too short, or “scalping,” places extreme stress on the plant by removing too much photosynthetic area. For Tall Fescue, the ideal mowing height is between 3 to 4 inches, especially during the summer, as this height shades the soil and promotes deeper root growth.
A common source of browning is chemical burn from the incorrect application of fertilizers or herbicides. Applying granular fertilizer when the grass blades are wet, or over-applying nitrogen in hot weather, can cause concentrated salts to draw moisture out of the leaves, resulting in scorching. This type of burn often appears as streaks or distinct, localized patches corresponding to the application pattern.
Accidental exposure to herbicides, such as misapplied weed killers or spillages, can cause immediate and severe discoloration. Broadleaf weed killers are designed to disrupt plant growth hormones, and high concentrations can cause the grass to turn yellow, curl, and die. Always ensure application equipment is clean and calibrated correctly to prevent these chemical injuries.
Identifying Dormancy Versus Permanent Damage
The final diagnostic step is determining if the brown grass is merely dormant or if it has suffered permanent damage. Tall Fescue enters dormancy as a survival mechanism during prolonged periods of heat and drought, effectively shutting down growth to protect the crown. A dormant lawn appears uniformly brown across the affected area, but the crown, located just above the soil line, may still retain a hint of green.
To test for dormancy, select a small brown patch and water it deeply for a few days, or perform a gentle tug test. If the grass resists being pulled out of the soil and the crowns show signs of life after watering, it is likely dormant and will recover once cooler temperatures return. In contrast, permanently damaged grass will be brittle, pull out of the soil with little resistance, and show a completely brown or gray appearance throughout the entire plant.