Frog-Eye Spots in Your Lawn: Which Fungal Diseases Create This Pattern in Texas

The term “frog-eye” in turf pathology describes a very specific visual pattern: a circular or oval dead zone in the lawn with a living green center — so that from above, the patch looks like an eye with a pupil. It’s one of the more descriptive terms in lawn disease diagnostics, and it’s useful because the pattern itself narrows your list of possible culprits significantly. In North Texas, frog-eye patterns are associated with a handful of serious fungal diseases, and getting the right lawn disease and fungus control response hinges on understanding which one you’re dealing with.

Why Frog-Eye Patterns Form

Frog-eye or target-spot patterns result from a specific type of fungal disease progression. The infection begins at a central point and spreads outward in a ring. As the active infection front moves outward, the center — where the fungus was earliest — either recovers (if the pathogen is primarily a blade or canopy disease that doesn’t kill crowns), becomes colonized by weeds, or is replaced by regrowth. Meanwhile the outer ring remains the zone of active fungal attack, producing a ring of dead or stressed turf surrounding a living center. The diameter of the frog-eye pattern ranges from a few inches to several feet depending on how long the disease has been active and how fast it spreads.

Necrotic Ring Spot in Fescue and Bluegrass

Necrotic ring spot, caused by Ophiosphaerella korrae, is one of the most textbook frog-eye diseases in the turf world and occurs in North Texas on tall fescue lawns — particularly overseeded or established cool-season fescue areas in parts of DFW. The disease infects roots and crowns during cooler weather (spring and fall) while causing visible symptoms during summer stress when the diseased root system can’t support the turf through heat and drought.

Classic necrotic ring spot frog-eye features:

• Circular rings 6 inches to 3 feet in diameter: The rings are typically fairly well-defined with dead or straw-colored turf in the ring zone and surviving — sometimes even lush — grass in the center where root damage was less severe.
• Center survivors are often weeds or disease-tolerant fescue plants: The green center of a necrotic ring spot frog-eye is frequently populated by annual bluegrass, crabgrass, or other weeds that colonize the stress-weakened areas, plus whatever disease-resistant individual plants survived the infection.
• Root damage that confirms the diagnosis: Pulling runners from the ring zone reveals darkened, decayed roots characteristic of Ophiosphaerella infection — the same root rot signature seen in spring dead spot, which is caused by a closely related pathogen in the same genus.

Dollar Spot Frog-Eye in Early Stages

Dollar spot disease, caused by Clarireedia jacksonii, typically presents as small individual dead spots the size of a silver dollar in Bermuda, zoysiagrass, and occasionally St. Augustine lawns. However, when multiple dollar spot infections coalesce into larger patches and the center of a patch begins to recover while the expanding perimeter remains active, the pattern takes on a frog-eye or ring-like appearance. This is more commonly seen in lawns where dollar spot has been active for several weeks without treatment.

Dollar spot characteristics that distinguish it from other frog-eye diseases:

• Straw-colored lesions with reddish-brown borders on individual blades: The signature dollar spot blade symptom — an hourglass-shaped or banded lesion crossing the full width of the grass blade with tan or straw coloring and a dark reddish-brown margin — is visible on blades at the active ring perimeter.
• Fine white mycelium in early morning: Dollar spot produces delicate, spider web-like mycelium visible at the patch edge before morning dew evaporates.
• Nitrogen-deficient turf is the highest-risk population: Dollar spot is strongly associated with low-nitrogen turf. A frog-eye pattern on an under-fertilized Bermuda or zoysia lawn in late spring or fall strongly suggests dollar spot as a contributing factor.

Brown Patch Frog-Eye in St. Augustine and Zoysia

Brown patch, caused by Rhizoctonia solani, is the most common lawn disease in North Texas and typically presents as irregular circular patches. In some cases — particularly in St. Augustine lawns — expanding brown patch rings develop a frog-eye appearance when the center of an older patch begins to recover while the ring perimeter continues to advance. The green center in a brown patch frog-eye is often genuinely recovering turf, because brown patch primarily kills blade tissue rather than crowns, and the plant can regrow once the active infection front moves past.

The key distinguishing features from necrotic ring spot or dollar spot:

• Timing and temperature: Brown patch is strictly a warm-weather disease in North Texas, most active when nighttime temperatures exceed 70°F. Necrotic ring spot symptoms appear during summer stress but infection occurs in cool weather. Dollar spot peaks in transition seasons.
• Blade death without crown or root damage initially: Brown patch in its early to mid stages leaves the crown intact. The smoke ring at the active margin, visible mycelium at the patch edge in morning, and blade-only lesions without root rot confirm Rhizoctonia over other frog-eye causes.

Distinguishing Frog-Eye Disease from Other Ring-Like Patterns

Not every ring in a lawn is a frog-eye disease. Several non-fungal conditions create similar patterns:

• Irrigation coverage gaps: Sprinkler heads with reduced output create circular dry zones that look like disease rings from a distance. Check whether the pattern correlates with sprinkler head locations and whether the apparent “ring” is actually uniform drought stress rather than a ring of dead turf with a living center.
• Dog urine spots: Repeated urine deposition creates circular nitrogen burn spots with a ring of lush dark green grass at the outer margin — the reverse of a typical frog-eye. The center is dead and the outer ring is green and over-fertilized.
• Fairy ring Type 2: A ring of lush, dark green grass (not dead grass) is fairy ring, not a fungal disease attacking the turf. Fairy ring releases nitrogen as it decomposes organic matter, producing the green ring, and doesn’t produce a dead-center frog-eye unless progressing to Type 1.

Treatment Approach by Disease

The frog-eye pattern narrows your diagnosis but doesn’t select your treatment — that requires confirming which disease is responsible:

• Necrotic ring spot: Responds to azoxystrobin and fenarimol applied preventively; cultural improvement through aeration, pH management, and irrigation timing is equally important for long-term suppression.
• Dollar spot: Nitrogen fertilization to restore growth rate plus fungicides containing propiconazole, iprodione, or boscalid applied during active disease pressure.
• Brown patch: Azoxystrobin, flutolanil, or fluxapyroxad applied at the first sign of active spread; cultural correction of irrigation timing and nitrogen inputs to reduce recurrence.

Frog-eye spots are one of the clearest signals your lawn sends that a fungal disease is in the middle of a spreading event. Hamann has been reading these patterns in Arlington and DFW since 2006. Our lawn disease and fungus control service correctly identifies the cause and matches the right chemistry to the right disease — which is the only way to actually stop it. Also see our post on orange residue on shoes from lawn rust fungus for another visually distinctive fungal symptom common in North Texas lawns.