Pythium Blight: Symptoms and Controlby Harrell's

Blog, Golf June 10, 2010 8:57 am

Prepared by members of the Departments of Plant Pathology and Crop Science, College of Agriculture & Life Sciences, North Carolina State University. For more turf-related information, visit the NC State TurfFiles web site.

Symptoms

Pythium blight first appears as small, sunken, circular patches up to 1 foot in diameter during hot, humid weather. Leaves within the patches are matted, orange or dark gray in color, and greasy in appearance. Gray, cottony mycelium may be seen in the infected areas when the leaves are wet or humidity is high. The disease spreads rapidly along drainage patterns and can be tracked by equipment. This disease can spread rapidly and cause severe damage to a turf stand very quickly when conditions are favorable for development.

Characteristic	Description
Host Grass Species	Bentgrass, bluegrasses, fescues, ryegrass
Month(s) with Symptoms	June to August
Stand Symptoms	Patches (4 to 12 inches), irregular distribution across turf stand
Foliar Symptoms – Location / Shape	Blighting of entire leaves
Foliar Symptoms – Color	Tan, brown, black, gray, orange
Root / Crown Symptoms	None
Fungal Signs	Mycelium or none

Note: Still not sure if this is the right disease? The Turfgrass Disease Identification program may be helpful. Or consult the experts at the Turf Diagnostics Lab. Check the TurfFiles glossary for definitions of unfamiliar terms.

Pythium blight mycellium in tall fescue

Factors Affecting Disease Development

Pythium blight may develop when night temperatures exceed 65°F and leaves are continually wet for 12 to 14 hours for several consecutive nights. Daytime temperatures above 85°F also encourage Pythium blight development, possibly due to increased stress on the turf.  Severe Pythium blight epidemics are commonly observed the morning after a late afternoon or early evening thunderstorm in the summer. Excessive soil moisture and succulent foliar growth also favor disease development.

Perennial ryegrass and annual bluegrass are most prone to Pythium blight and can sustain significant damage in 2 to 3 days when conditions are favorable. Creeping bentgrass and tall fescue are more resistant to the disease, but can be severely affected if conditions are conducive for prolonged periods.

Cultural Control

Reduce prolonged leaf wetness by watering before sunrise and on a deep and infrequent basis. Avoid excessive rates of nitrogen to prevent lush, succulent foliar growth, which is very susceptible to Pythium blight. Cool-season turfgrasses should not be fertilized with more than 0.25 lb N per 1000 ft2 when conditions favor Pythium blight activity. Avoid establishing turf in low-lying areas that will collect water. If necessary, install subsurface drainage to prevent wet soil conditions. Relieve compaction and maintain soil drainage through hollow tine aerification, and topdress golf course putting greens regularly to minimize thatch accumulations.

Do not mow or irrigate when Pythium mycelium is present on the foliage to minimize spread of the pathogen. Collect and promptly dispose of clippings from infected areas and ensure that mowing equipment is washed before going to an uninfected area.

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