Lawn diseases and pests are diagnosed by examining patch geometry, foliar lesion patterns, and root integrity. Fungal pathogens like Brown Patch (Rhizoctonia solani) and Dollar Spot thrive in high humidity and improper irrigation, whereas pests like White Grubs sever root systems beneath the sod. Use the interactive symptom decision tree below to diagnose lawn damage and select university-verified cultural and chemical treatments.
Select your visual symptom pattern, host grass, and temperature conditions to identify pathogens and match curative active ingredients.
Rhizoctonia solani
Circular tan or brown patches ranging from several inches to several feet in diameter. During high morning humidity, dark purplish "smoke rings" appear along the outer perimeter where fungal hyphae actively infect new foliage.
Halt late evening irrigation immediately; irrigate only between 4:00 AM and 8:00 AM. Avoid high-nitrogen summer fertilization which produces soft, succulent leaf tissue prone to infection.
Apply systemic strobilurin or DMI fungicides: Azoxystrobin (Heritage G) or Propiconazole (Banner MAXX). Re-apply in 14–28 days if disease pressure persists.
Professional active formulations cross-referenced against university disease and pest trials.
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Formula: 0.31% Azoxystrobin Broad-Spectrum
Granular broad-spectrum systemic fungicide delivering 28-day preventive and curative control of 20+ turf diseases.
Connect with licensed regional plant health care technicians and certified pesticide applicators.
Lawn fungal diseases are infectious plant pathologies caused by microscopic fungal organisms that inhabit soil, thatch, and decaying organic debris. Unlike weeds or environmental abiotic stresses (such as dog urine spots or mower burn), fungal pathogens require three simultaneous factors known as the Plant Disease Triangle: a susceptible host turfgrass plant, an active virulent pathogen, and favorable environmental conditions (predominantly prolonged leaf wetness and specific temperature bands).
Before treating a discolored lawn, first confirm your grass species using our blade trait identification key. Cultivars exhibit dramatically different pathogen susceptibilities: Tall Fescue and Perennial Ryegrass are primary hosts for Brown Patch (Rhizoctonia solani), Kentucky Bluegrass is susceptible to Summer Patch (Magnaporthiopsis poae), and St. Augustine Grass is commonly impacted by Large Patch and Take-All Root Rot.
Agronomists differentiate lawn diseases across four morphological diagnostic patterns:
Brown Patch manifests as irregular to circular patches ranging from 6 inches to several feet in diameter. During high early morning humidity, an active "smoke ring" composed of fungal mycelium and water-soaked, decaying blades outlines the border of expanding infection circles.
Dollar Spot (Clarireedia jacksonii) appears as small, silver-dollar-sized circles of bleached straw-colored turf. On individual grass blades, lesions exhibit characteristic hourglass shapes with reddish-brown margins. Dollar spot thrives on nitrogen-deficient lawns.
Ectotrophic root-infecting fungi colonize subterranean roots and crowns in late spring when soil temperatures reach 65°F, though foliar symptoms appear in summer heat. Patches form classic "frog-eye" doughnut patterns where healthy grass survives in the center while the outer perimeter dies.
White Grubs (larvae of Japanese beetles, masked chafers, and May/June beetles) feed voraciously on turfgrass roots in late summer and autumn. Infested lawns become spongy and can be lifted off the soil bed like a loose carpet, revealing curled white larvae underneath.
Rhizoctonia solani
Leaves exhibit water-soaked dark lesions that dry into irregular tan spots with dark brown margins. Turf crowns remain green.
Avoid evening irrigation; water only between 4:00 AM and 8:00 AM. Reduce synthetic nitrogen fertilization during July and August.
Chemical Active (Azoxystrobin (QoI / Group 11 Fungicide) & Propiconazole (DMI / Group 3 Fungicide)):Azoxystrobin (Heritage G) or Propiconazole (Banner MAXX) applied at 14–21 day intervals during hot, humid spells.
Clarireedia jacksonii
Individual leaf blades show bleached hourglass lesions with distinct reddish-brown borders. White cobwebby mycelium visible in morning dew.
Apply light spoon-feedings of quick-release nitrogen. Irrigate deeply in early morning to knock down dew.
Chemical Active (Propiconazole (Group 3) & Myclobutanil (Group 3)):Propiconazole, Myclobutanil (Eagle 20EW), or Boscalid.
Pythium aphanidermatum
Blades feel slimy and oily; distinct cottony white fungal mycelium in morning; turf collapses and dies within 24 hours.
Core aerate compacted ground to relieve drainage. Never water hot turf in late afternoon. Avoid mowing wet infected grass.
Chemical Active (Mefenoxam (Group 4) & Cyazofamid (Group 21)):Mefenoxam (Subdue MAXX) or Cyazofamid (Segway).
Magnaporthiopsis poae
Roots turn dark brown to black and slough off; turf pulls up effortlessly from soil like a carpet.
Acidify rootzone using ammonium sulfate fertilizer; Summer Patch pathogen is suppressed at soil pH <6.0.
Chemical Active (Azoxystrobin (Group 11)):Preventative Azoxystrobin or Pyraclostrobin applied in spring when soil temp reaches 65°F at 2-inch depth.
Puccinia spp.
Powdery orange fungal pustules on leaf blades that easily rub off onto shoes, pets, and mower wheels.
Apply 0.5 lb nitrogen per 1,000 sq ft to stimulate active growth. Mow frequently to remove infected leaf tips.
Chemical Active (Myclobutanil (Group 3)):Myclobutanil or Propiconazole (chemical control rarely needed in residential lawns).
Laetisaria fuciformis
Bright coral-red brittle fungal threads (sclerotia) extending from leaf tips.
Apply moderate nitrogen application (0.5 to 1.0 lb N/1,000 sq ft) to outgrow the disease.
Chemical Active (Azoxystrobin (Group 11)):Azoxystrobin or Flutolanil (ProStar).
Phyllophaga spp. / Popillia japonica
Turf pulls back effortlessly with zero root anchoring; fat C-shaped creamy white grubs visible in top 1-2 inches of soil (>5–10 grubs per sq ft).
Deep infrequent irrigation to drive grass roots deep; apply beneficial nematodes (*Heterorhabditis bacteriophora*).
Chemical Active (Chlorantraniliprole (Preventative) & Trichlorfon (Curative)):Chlorantraniliprole (Scott’s GrubEx) preventative in May–June; Trichlorfon (Dylox) curative in late summer.
Blissus leucopterus
Insect injects toxic saliva while sucking sap; small black insects with white wing patches and reddish nymphs visible at thatch line.
Dethatch lawn and maintain adequate irrigation in sunny focal areas. Use endophyte-enhanced fescues and ryegrasses.
Chemical Active (Bifenthrin (Pyrethroid) & Imidacloprid (Neonicotinoid)):Bifenthrin (Talstar PL) or Imidacloprid applied with thorough watering to push active ingredient into thatch.
Solenopsis invicta
Aggressive stinging reddish-brown ants boiling out of disturbed soil mounds within seconds.
Broadcast ant bait in late afternoon when worker ants are actively foraging at soil temperatures of 70°F–90°F.
Chemical Active (Indoxacarb (Bait) & Bifenthrin (Contact insecticide)):Two-Step Method: Broadcast bait (Hydramethylnon / Indoxacarb) followed by mound drench (Bifenthrin).
Broad-spectrum systemic strobilurin (Azoxystrobin, FRAC 11) treating Brown Patch, Dollar Spot, Powdery Mildew, and Necrotic Ring.
Check Price on Amazon →Fast-acting organophosphate curative (Dylox / Trichlorfon) halting active Japanese beetle and masked chafer root feeding on contact.
Check Price on Amazon →While chemical fungicides offer effective curative intervention, sound cultural practices prevent 80% of fungal outbreaks. Fungal pathogens require free water on leaf surfaces to infect plants. By shifting irrigation schedules from evening to early morning (between 4:00 AM and 8:00 AM), leaf blades dry rapidly once the sun rises, denying fungal spores the 10+ hours of continuous moisture required for germination.
Furthermore, when chemical fungicides are necessary, applicators must follow the Fungicide Resistance Action Committee (FRAC) rotation guidelines. Repeatedly applying single-site inhibitors like Azoxystrobin (FRAC Group 11, QoI) induces resistant fungal strains. Professional programs rotate with demethylation inhibitors (FRAC Group 3, DMI like Propiconazole) or multi-site contact protectants like Chlorothalonil to guarantee long-term efficacy.
Keep your lawn canopy healthy and resilient by maintaining appropriate nitrogen balances through our lawn fertilizer nutrient calculator, and prevent weed stress by reviewing our selective herbicide tolerance matrix.
Brown Patch produces large circular tan patches (up to 3–6 feet in diameter) with dark purple or smoky-brown outer margins on tall fescue and perennial ryegrass during hot, humid nights (>68°F). Dollar Spot produces small, discrete bleached circles (2–4 inches in diameter) with distinct hourglass-shaped lesions on individual leaf blades, occurring during warm days and cool humid nights on nitrogen-deficient turf.
Preventive fungicide applications should begin in late spring before daytime temperatures consistently exceed 80°F and night temperatures stay above 65°F. For high-risk lawns with a history of brown patch or summer patch, apply systemic fungicides like Azoxystrobin (FRAC Group 11) or Propiconazole (FRAC Group 3) on a 21 to 28-day schedule through mid-summer.
Perform the sod pull test: grab a handful of dead or discolored turf and pull upward. If the turf lifts easily like a loose rug with no root anchoring and you observe C-shaped white grubs in the top 2 inches of soil, you have a grub infestation. If the roots remain firmly anchored in the soil profile, the issue is moisture deficit or a foliar fungal disease.
Yes. Late evening irrigation keeps turf leaf blades wet for 10 to 14 consecutive hours overnight, which is the exact physiological moisture threshold required for fungal spores to germinate and penetrate plant cuticle cells. Always irrigate between 4:00 AM and 8:00 AM so morning sunlight and wind quickly dry the leaf canopy.
