Disease Symptoms

• The crowns of roots turn brown on plants infected with Pythium fungus. They also develop dark-brown lesions on their root tips. Pythium fungi initially manifest as mycelium, a white, branching, cobweb-like form of the disease. Mycelium appears in the morning when the soil is wet with dew or at times of poor air movement or circulation. Because of its cobweb-like appearance, one of the names for Pythium disease is "cottony blight." The University of Rhode Island Landscape Horticulture Program presents another name for Pythium fungus, "greasy spot," referring to the small, greasy or slimy areas appearing on infected blades of grass giving them a water-soaked look. When the infected grass has dried, these diseased areas become matted, turn light brown and sometimes slightly reddish. Infected areas have an irregular shape, and can appear as streaks traveling in the direction of the flow of moisture runoff in depressed surface areas.
  
  

Spreading the Disease

• Mowing infected grass will quickly spread this disease. Mycelium spread oospores, the resilient sexual spores of the fungi. Moving water or walking through infected areas also spread the oospores. Within days, Pythium infection kills large areas of turf.
  
  

Weather Conditions

• Pythium infection and disease can appear in any season under conditions of extreme heat and humidity. Summer temperatures of 80 to 95 degrees Fahrenheit and wet weather conditions during seasons with temperature ranges of 60 to 65 degrees Fahrenheit provide a fertile environment in which Pythium fungi thrive.
  
  In "Pythium Blight," Richard Latin, professor of Plant Pathology at Purdue University, states weather conditions causing dew to remain on the ground more than 14 hours are an additional factor in the occurrence of Pythium blight.
  
  

Disease Management

• The most favorable environments for Pythium disease are soil treated with high-nitrogen fertilizers, alkaline soil and soil with low calcium levels. A preventive measure recommended by the Cornell University Plant Disease Diagnostic Clinic is to use balanced fertilizers and keep your soil pH neutral or slightly acid. Purdue University Extension recommends improving drainage and pruning trees and shrubs to improve air circulation. The University of Rhode Island Landscape Horticulture Program recommends correcting drainage problems, avoid over-watering, and mowing areas with poor drainage last to minimize contamination of non-infected areas. It is best to mow when grass is dry.
  
  

Fungicides

• In "Pythium Blight," Richard Latin states, due to the capacity of Pythium fungi to spread rapidly, golf course superintendents routinely apply fungicide during excessively hot summers to avoid allowing this disease to become established. But fungicides specifically formulated to treat Pythium fungus are expensive. Obtain a positive diagnosis of the disease before making your purchase.