PYTHIUM ROOT DYSFUNCTION

Pythium root dysfunction soil cores	Characteristic	Description
	Host Grass Species	creeping bentgrass
	Month(s) with symptoms	all
	Stand Symptoms	patches (4 inches to greater than 3 feet)
	Foliar Symptoms - Location/Shape	dieback from leaf tip
	Foliar Symptoms - Color	orange, yellow
	Root/Crown Symptoms	roots tan and lacking root hairs
	Fungal Signs	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.

FACTORS AFFECTING DISEASE DEVELOPMENT

Pythium root dysfunction infects creeping bentgrass roots in the fall, winter, and spring when mean daily soil temperatures are between 50ºF and 75ºF. Disease activity reduces the turf’s ability to absorb water and nutrition from the soil, and also leads to rapid root dieback when soil temperatures exceed 85ºF. Therefore, the appearance of Pythium root dysfunction symptoms are enhanced by low fertility, drought stress, and low soil oxygen levels. Symptoms are most common during hot weather in summer but may also appear during warm, dry conditions in fall, winter, or spring.

CULTURAL CONTROL

Creeping bentgrass greens should be constructed with at least 15% organic matter by volume to provide adequate water and nutrient holding capacity. After establishment, creeping bentgrass should be fertilized with 4 to 6 lbs N per 1000 ft² annually. Use regular soil and tissue testing to ensure that all other nutrients are present in adequate amounts. Raise mowing heights above 0.125 in. during summer to increase photosynthesis and alleviate stress. Avoid severe drought stress by irrigating when symptoms of wilt become widespread, and supplement with syringing and hand-watering of areas that dry out more quickly. Soil surfactants increase the uniformity of soil moisture across putting greens and will assist with water management. Frequent cultivation and topdressing are needed to maximize oxygen levels in the soil. In general, 15% to 20% of the putting green surface area should be impacted by hollow-tine aerification annually, and 5000 lbs of topdressing should be applied per 1000 ft² each year. Biweekly solid-tine aeration during summer will increase root survival by creating temporary channels for air and water movement through the soil profile.

CHEMICAL CONTROL

Standard Pythium fungicides, such as mefanoxam (Subdue Maxx), propamocarb (Banol), and fosetyl-Al (Signature) have provided poor to moderate control of Pythium root dysfunction when applied alone. The most effective fungicides have been pyraclostrobin (Insignia 20WG) and cyazofamid (Segway). Applications watered in with 1/8" of irrigation immediately have been slightly more effective than standard foliar applications. The same result may also be obtained by making the applications in larger volumes of water (4 to 6 gallons per 1000 ft²) to drive the fungicide deeper into the canopy. Tank-mixtures of Signature + Banol (4 + 2 oz/1000 ft²) or Signature + Subdue Maxx (4 + 1 oz/1000 ft²) also have provided good disease suppression. These tank-mixtures are most effective when applied to the foliage in 2 gallons of water per 1000 ft².

Fungicides may be used on either a curative or preventative basis for Pythium root dysfunction control. Both strategies employ the same fungicide rotation:

1. Insignia (0.9 oz/1000 ft², watered-in with 1/8" of irrigation)

2. Segway (0.9 fl oz/1000 ft², watered-in with 1/8" of irrigation)

3. Signature + Banol (4 + 2 oz/1000 ft²) or Signature + Subdue Maxx (4 + 1 oz/1000 ft²) applied in 2 gal/1000 ft² and left on the foliage.

For preventative control, one of these treatments should be applied every 21 to 28 days in the fall and spring when mean daily soil temperatures are between 50ºF and 75ºF. Curative applications should be made every 14 to 28 days based on the appearance of symptoms. Effective curative control also requires increased mowing heights and nitrogen inputs to relieve stress and allow the affected plants to heal.

Because Insignia and Segway are prone to fungicide resistance, it is very important to follow the fungicide rotation outlined above. Superintendents who apply one fungicide repeatedly are likely to experience control failure as the fungal population becomes resistant.

© North Carolina State University. This information sheet was prepared by Lane P. Tredway, Gail G. Wilkerson, Bridget R. Lassiter, Jenifer J. Reynolds, and Gregory S. Buol. Departments of Plant Pathology and Crop Science, College of Agriculture & Life Sciences, North Carolina State University. Prepared March 23, 2009. Available on-line at www.turffiles.ncsu.edu. This publication was made possible through a grant provided by the Center for Turfgrass Environmental Research & Education (CENTERE) whose purpose is to support worthwhile projects that will benefit both the private sector and the public, and protect the environment.