The appearance of brown, dead patches in an otherwise healthy lawn is frustrating for any homeowner. This localized damage suggests a specific underlying issue, ranging from a hidden insect infestation to a soil chemistry problem. Successfully restoring the turf requires correctly diagnosing the cause, as the treatment for pests differs drastically from the solution for fungal infections or chemical burns. This guide examines the three primary categories of lawn distress to help pinpoint the source of the patchy die-off.
Identifying Lawn Pests
When grass dies in patches, especially during the summer and early fall, subsurface insects are often the culprits. These pests target the root structure, and the resulting damage often looks similar to drought stress.
Grubs
Grubs, the larvae of various beetles, commonly cause irregular brown areas by feeding directly on the grass roots just below the soil surface. To check for these C-shaped white larvae, perform the “tug test” on the affected turf. If the grass in a brown patch pulls up easily, separating from the soil, it confirms that the roots have been severed. The soil in these areas may also feel spongy underfoot.
Chinch Bugs
Chinch bugs are tiny surface feeders that inject a toxic substance into the grass blade while sucking out the plant’s fluids. Damage first appears as irregular yellowing patches in the hottest, sunniest areas, gradually turning brown as the grass dies. To confirm their presence, carefully part the grass at the border between the healthy and dying turf. If an infestation is active, you will see numerous small, black bugs with white wing markings scurrying across the thatch layer.
Insect-related problems require a targeted approach, typically involving the application of an appropriate insecticide. Timing the application to coincide with the most vulnerable stage of the insect’s life cycle is a significant factor in achieving effective control.
Recognizing Fungal Infections
Lawn diseases, typically caused by fungi, create distinct visual patterns that help differentiate them from insect damage. These pathogens thrive under specific environmental conditions, such as high humidity or prolonged leaf wetness.
Brown Patch
Brown Patch disease, caused by the fungus Rhizoctonia solani, produces roughly circular or irregular areas of brown, thinned turf. These patches can range from six inches to several feet in diameter. A telltale sign of an active infection is a faint dark gray or black border, often called a “smoke ring,” visible around the perimeter of the patch, especially in the morning. This disease is prevalent when nighttime temperatures stay above 68°F combined with extended periods of leaf wetness.
Dollar Spot
Dollar Spot is characterized by small, bleached-out circular spots, usually one to six inches across, resembling the size of a silver dollar. The individual grass blades within these spots display tan lesions with reddish-brown margins, often constricting the blade in an hourglass shape. This fungus is active when moderate temperatures (60°F to 85°F) combine with moisture stress or low nitrogen levels.
Fairy Rings
Fairy Rings are caused by fungi that break down organic matter in the soil, resulting in a variety of circular patterns. The most destructive form appears as a ring of dead, brown grass because the fungal growth makes the soil water-repellant. Other types manifest as a dark green, fast-growing ring of grass, or sometimes just a ring of mushrooms. Management involves improving air circulation, watering early in the day, and applying a fungicide to reduce favorable conditions.
Environmental and Cultural Causes
Many non-biological factors, related to human activity or localized environmental conditions, can create patches of dead grass. These causes frequently leave behind patterns that indicate their origin, making them easier to diagnose than pests or fungi.
Chemical Burns
Chemical burn results from the uneven application of granular fertilizer or an accidental spill, causing an excess concentration of mineral salts that draw moisture out of the grass. The damage appears as sharply defined yellow or brown patches, or sometimes as stripes following the application path of a spreader. Similar damage occurs from herbicide overspray, which often leaves linear or distinct scorch marks.
Pet Urine
Pet urine, particularly from dogs, causes a distinct type of nitrogen burn due to its high concentration of nitrogen and salts. This results in a small, dead, bleached-out patch at the center. This patch is frequently surrounded by a ring of unusually dark green, faster-growing grass. The nitrogen concentration is toxic in the center, while the diluted nitrogen at the perimeter acts as a fertilizer, creating this characteristic halo effect.
Water Stress and Mechanical Damage
Localized water stress accounts for many patchy die-offs, often due to poor sprinkler coverage or soil issues. Areas near concrete or fences dry out faster, and misaligned sprinkler heads can miss spots. This leads to localized drought stress where the grass turns a dull, grayish-blue color and remains flattened after being walked on. Mechanical damage, such as a localized oil or gas spill from lawn equipment, will also create a dead patch with a distinct perimeter and a noticeable odor.