Imagine walking outside one morning to find greasy-looking patches of matted grass, almost as if the turf has melted. The cause of this is a lawn disease known as Pythium Blight (also known as grease spot or cottony blight), and it is one of the most aggressive and fast-moving lawn diseases that homeowners across Virginia may encounter during hot, humid conditions.
The Blue Sky team is here to help you recognize, prevent, and combat Pythium Blight. Keep reading to take back control of your Chantilly landscape before it’s too late!
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Pythium Blight is triggered by the pathogen Pythium aphanidermatum, which thrives in hot, humid weather and spreads rapidly through moist, saturated turf. When this disease takes hold, it often appears as greasy, discolored patches that quickly deteriorate and turn brown.
Symptoms often start as small, circular patches of water-soaked grass, particularly in areas with poor drainage or heavy thatch. As the disease advances, affected turf begins to collapse into greasy, tangled clumps that may appear slimy or matted. These patches often have a grayish-white cottony growth early in the morning when dew is present, which is actually the mycelium of the Pythium fungus.
Key Identifiers:
Pythium Blight is caused by soilborne organisms called oomycetes, sometimes referred to as water molds. These pathogens are highly opportunistic, taking advantage of stressed, waterlogged, or poorly maintained turf. Pythium spores exist in many lawns at low levels but only become problematic when specific environmental triggers align. High nitrogen content and excess moisture are some of the most common contributing factors.
Contributing Factors:
Pythium Blight thrives in warm, wet conditions and can spread through both environmental factors and physical contact. It is often seen in cool-season grasses like tall fescue and annual bluegrass but can affect a wide range of turf types. Pythium species favor environments with prolonged moisture and high humidity. Conditions become especially favorable when daytime temperatures are above 85°F and nighttime temperatures stay above 65°F for cool-season grass and 50°F for warm-season types.
It moves swiftly through poorly drained soil, dense turf, and compacted areas, making heavily trafficked or overwatered lawns especially vulnerable. Overwatering or watering at the wrong time can dramatically accelerate its spread. Visible mycelium in the early morning is a warning sign that conditions are ideal for an outbreak, and active spores are often transferred via lawn mowers, foot traffic, wind, and water.
It’s important to remember that Pythium Blight is both a foliar and root-infecting disease, meaning it will completely destroy and kill your grass if it is not dealt with. Pythium Blight is best managed through cultural practices that reduce stress and moisture on the lawn. The key is to create an environment where the turf thrives but fungal pathogens do not.
Fungicide use is the most effective way to combat Pythium Blight. Products containing active ingredients like mefenoxam or metalaxyl are known to suppress the disease when applied correctly. For best results, fungicides should be applied preventively starting in late spring or early summer. In regions or properties with a known history of Pythium outbreaks, applications every two weeks may be required during high-risk periods.
Timing is critical, so consult a professional for guidance on product selection and application strategy. If you suspect your lawn is experiencing a Pythium Blight outbreak, don’t delay! Contact Blue Sky today to schedule professional lawn care and landscaping consultation to help you prevent and control lawn diseases on your Virginia property!
