Pythium Root Rot is a destructive fungal disease that affects both warm- and cool-season turf grasses. It thrives in warm, humid conditions—particularly during the Australian spring and summer—when increased rainfall or excessive irrigation creates the perfect environment for fungal development.
Pythium can infect either the foliage (Pythium Blight) or the root system (Pythium Root Rot). While good cultural practices—such as reducing thatch, improving aeration, and managing irrigation—can help reduce stress on turf, the most effective control for Pythium Root Rot is the timely application of a suitable fungicide.
Pythium Root Rot is caused by several species of Pythium and most commonly affects lawns that are stressed, overwatered, or poorly drained. It is an aggressive disease that can spread rapidly and destroy large areas of turf within days, making early identification and prompt treatment essential. Preventative applications are also recommended when weather conditions are favourable for disease development.
Early symptoms appear as small, circular patches of discoloured turf, typically 2–5 cm in diameter but sometimes expanding to 15 cm or more. Infected grass often feels soft or slimy when handled. As the disease progresses, affected areas darken to brown, indicating advanced root damage and turf decline.
Pythium thrives in excessively wet soils and humid environments. Newly established or recently renovated lawns are particularly vulnerable due to frequent watering. The disease is commonly associated with:
Heavy summer rainfall
Extreme heat combined with over-irrigation
Compacted or poorly drained soils
Because Pythium organisms are present in most soil types, any lawn that remains waterlogged or overly moist is at increased risk of infection.
Pythium Root Rot can affect a wide range of turf varieties, including:
Warm-season grasses:
Couch / Bermuda
Buffalo
Kikuyu
Zoysia
Cool-season grasses:
Ryegrass
Kentucky Bluegrass
Fescue
Bentgrass
Although both diseases are caused by Pythium species, they differ in how they affect turf:
Pythium Blight attacks the leaves, producing greasy, water-soaked patches or white, web-like growth—often visible in the early morning. It leads to leaf discolouration and tissue death.
Pythium Root Rot is more severe, targeting the root system in saturated soils. It causes rapid turf collapse and is typically linked to excessive rainfall, poor drainage, or overwatering.
1. Improve Drainage and Aeration
Aerate lawns annually to relieve compaction and improve water and air movement.
Correct drainage issues to prevent water pooling around the root zone.
2. Manage Irrigation
Water deeply but less frequently to encourage deeper root systems.
Irrigate early in the morning so turf can dry during the day.
3. Control Thatch Build-Up
Excess thatch traps moisture and promotes fungal growth.
Dethatch regularly using vertimowing, scarifying, or grooming techniques.
4. Apply Balanced Nutrition
Avoid excessive nitrogen, which encourages soft, disease-prone growth.
Use a balanced fertiliser to support strong, resilient turf.
Only a limited number of fungicides are registered for home use against Pythium Root Rot. One of the most effective options is Mancozeb DG Contact Fungicide. Always follow label directions carefully and wear appropriate protective equipment during application.
Pythium Root Rot can spread rapidly during wet Australian summers or periods of above-average rainfall. However, with proper lawn care practices and the use of effective fungicides, this damaging disease can be successfully prevented and controlled. Visit our online store to explore a range of fungicide solutions to protect your lawn.
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