Pythium - Cool Season

Pythium sp. (Several) Also called Pythium Crown and Root Rot


This is an often unrecognized or misdiagnosed disease that causes deterioration in turfgrass roots resulting in slower growth, yellowing and stunting of roots and general decline and thinning of the infected turfgrass stand.

• A telltale sign of infection in the spring is when turf is slow to come out of dormancy, growing less vigorously when compared to surrounding healthy turf and responds poorly to fertilizer applications. Symptoms become more obvious between March and June as infected areas take on a patchy appearance with yellowish-orange to reddish-brown circular or irregular shaped spots from 4 to 7 cm in diameter. The disease can be mistaken for Pink snow mould early in the spring and later for Dollar spot or Necrotic ring spot.

• In the fall, patches can be pronounced, looking chlorotic with a tan to brown colour. If not diagnosed, these weak areas will eventually wilt and die.

• Visually, there is no mycelium present when compared to Pythium foliar leaf blight.

Turfgrasses Effected

Most often found on highly maintained turf surfaces including bentgrass and poa greens, aprons and approach areas, and tees. The disease can be found on newly established or mature turfgrass, with disease activity dependent on wet and cool weather conditions.


Two primary periods including early spring following snowmelt (March to May), and in late autumn (October to November) under cool and wet weather conditions with daytime temperatures from 10°-18°C and nighttime temperatures: from 7°-13°C.

Control Options

• Maintain a vigorous root system and minimize the presence of excessive moisture
• Use a balanced fertility program
• Aerate to improve drainage
• Promote good air circulation around problem areas
• Apply ALIETTE T&O either in spring or fall applications


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