G1912

Pythium Blight of Turfgrass

Causes, symptoms and management of pythium blight disease in turfgrass. This is one in a series of NebGuides on managing turfgrass diseases.

• Cause, Hosts and Occurrence
• Key Symptoms and Signs
• Cultural/Maintenance Practices
• Fungicide Program

Figure 1. Symptoms of Pythium blight, showing irregular blighted areas of affected turf. Note that dead shoots may feel greasy and will have cottony mycelium growth in morning or when wet. (Photo: A. Ziems)

Pythium blight occurs during wet weather and in high maintenance landscapes that are frequently watered. It can be managed by altering moisture availability when possible and by using fungicides. The following information describes the disease and how to identify and manage it.

Cause, Hosts and Occurrence

Cause: Pythium aphanidermatum, P. graminicola, other Pythium spp.

Primary Hosts: Perennial ryegrass, Creeping bentgrass, Annual bluegrass

Occurrence: July – August

Key Symptoms and Signs

• Roughly circular, reddish-brown spots or streaks that suddenly appear (Figure 1).
  
  
• In morning dew, infected grass leaves appear water-soaked, slimy to the touch, and dark green.
  
  
• Presence of cottonball-like mycelium in early morning.
  
  
• Affected turf may give off a fishy odor. This will be especially evident if a sample is bagged overnight.
  
  
• Commonly observed in new seedings of perennial ryegrass and annual bluegrass.

Cultural/Maintenance Practices

• Provide adequate soil drainage.
  
  
• Fill depressions where water stands.
  
  
• Thin landscape plantings to promote good air movement across the turf.
  
  
• Avoid mowing and trafficking wet turf.
  
  
• Use a balanced fertilizer program that will meet the nutritional needs of the turf but not stimulate lush growth during summer.
  
  
• Avoid overwatering and late-afternoon/early-evening watering during periods of hot, humid weather.
  
  
• Aerate to reduce thatch accumulation.
  
  
• When establishing new turf areas, do not saturate the soil on newly seeded areas, and remove mulch immediately after seedlings emerge.

Fungicide Program

• Preventive Program:
  • First application in mid-June or earlier using a systemic fungicide. The first treatment should be made when the 24-hour forecast calls for favorable weather (daytime temperatures above 90°F, night time temperatures above 65°F, 80 percent or greater relative humidity).
  • Second application two weeks later, also using a systemic fungicide.
  • Third application of a contact fungicide should be made two weeks after the second application.
    
    
• Curative Program:
  • Curative measures using contact fungicides can be used on less valuable turf areas and those less prone to Pythium blight or when blight symptoms first appear. A short spray interval of seven days may be needed under high-disease pressure.

Fungicides for Pythium blight are presented in Table I. Product examples are provided for each active ingredient, but not all products are listed. Homeowner and commercial product labels will list active ingredients. While the active ingredient may be in combination with others, users should look for a specific active ingredient with or without other chemistry modes of action.

Fungicides listed represent the best information available. Read and follow all product label directions for mixing and application.

This publication has been peer reviewed.