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Pythium Blight

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  • Affects mostly tall fescue and perennial rye grass; not common in blue rye
  • Most common during July thru September (higher humidity and warmer weather)
  • Main cause — Keeping the leaf surface continuously wet (daily watering).
  • Symptoms — Circular patches of water soaked looking leaves that turn copper-colored, dark brown or black and feel greasy. Fungal strands may be visible during the early morning or evening hours. The infected spots, if not treated, can quickly run together destroying large patches of lawn within a 24 hour period!
  • Cultural Practices — to minimize chances of disease:
    • Use a balanced fertilizer, but avoid applying high rates of Nitrogen, particularly in late spring and summer
    • Water during early AM hours to allow grass leaves all day to dry off
    • Avoid frequent irrigation that keeps the leaf blades wet and that results in water logged/compacted soils
    • Mow at the upper end of recommended mowing heights (but not above recommended mowing heights) 
  • Spray on a fungicide labeled for Pythium Blight if symptoms appear… repeat every 10 days until symptoms are gone…Pythium requires a different fungicide than what is recommended for most fungi that are common to Southern California ...ALWAYS READ & FOLLOW LABELED DIRECTIONS!