Pythium aphanidermatum
Pythium Blight (Grease Spot) (Pythium aphanidermatum) is a serious fungal disease affecting Perennial Ryegrass, Kentucky Bluegrass, Tall Fescue, Bermudagrass. It triggers under extreme heat (daytime >85°f, nighttime >70°f) in waterlogged, poorly drained soils with 100% humidity. Symptom manifestation begins with blades feel slimy and oily; distinct cottony white fungal mycelium in morning; turf collapses and dies within 24 hours. Curative control requires Mefenoxam (Subdue MAXX) or Cyazofamid (Segway).
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Curative treatment of Pythium Blight (Grease Spot) requires strict adherence to statutory EPA product label directions. University extension trials demonstrate high efficacy with the following commercial chemistries:
Broad-spectrum systemic strobilurin (Azoxystrobin, FRAC 11) for curative and preventative control of turf fungi.
Check Price on Amazon →High-potency organophosphate (Dylox / Trichlorfon) curative halting subterranean insect damage within 24 hours.
Check Price on Amazon →Pathogen virulence operates strictly under the classic Plant Disease Triangle: infection requires an active pathogen inoculum, a genetically susceptible turfgrass host, and conducive microclimatic conditions (primarily prolonged leaf canopy moisture exceeding 10 consecutive hours combined with elevated rootzone humidity). Unmown or excessively dense turf stands impede airflow, creating an insulated stagnant microclimate where fungal spore germination accelerates.
When evaluating suspect turf patches, cross-examine rootzone integrity against foliar discoloration. True root-rot pathogens compromise subterranean anchoring, allowing turfgrass mats to be pulled up effortlessly with zero tensile resistance. In contrast, foliar blights damage leaf blades while leaving crown tissue and primary adventitious roots viable for regenerative recovery once fungicide active ingredients are introduced.
Cultural Protocol: Core aerate compacted ground to relieve drainage. Never water hot turf in late afternoon. Avoid mowing wet infected grass. Always avoid excess evening irrigation; irrigate early between 4:00 AM and 8:00 AM to allow rapid sun-drying of turf foliage. Keep cutting blades sharp to minimize ragged blade wounds through which fungal hyphae penetrate.
Chemical Protocol: Mefenoxam (Subdue MAXX) or Cyazofamid (Segway). Rotate active ingredients across different FRAC / IRAC mode-of-action groups (such as rotating Group 11 strobilurins with Group 3 triazoles) to prevent resistant fungal strains from dominating your lawn ecosystem.
Pythium Blight (Grease Spot) is recognized by Dark greasy purple-black patches turning straw-brown. forming 2 to 6 inches rapidly coalescing into long drainage streaks.. Blade symptoms: Blades feel slimy and oily; distinct cottony white fungal mycelium in morning; turf collapses and dies within 24 hours.
Primary susceptible hosts include Perennial Ryegrass, Kentucky Bluegrass, Tall Fescue, Bermudagrass. Maintaining proper fertilization and irrigation reduces pathogen virulence.
Extension-recommended treatment: Mefenoxam (Subdue MAXX) or Cyazofamid (Segway). Active ingredient: Mefenoxam (Group 4) & Cyazofamid (Group 21).
Core aerate compacted ground to relieve drainage. Never water hot turf in late afternoon. Avoid mowing wet infected grass.
