Magazine: Pythium Blight Of Turfgrass

By Jerry Spencer in Consultancy on 3rd May 2008 17:25

All turfgrasses are susceptible to attack by Pythium spp. The first symptoms of Pythium blight are irregularly shaped or evenly streaked, reddish brown spots in the turf, ranging in diameter from 3 to 15 cm. In the morning dew, infected blades appear water-soaked and dark, and feel greasy.

When the spots are wet with dew, cottony, purplish-gray or white mycelia may be evident.

Pythium species can cause a number of diseases which can be divided into 1) seedling damping off, 2)root and crown rot, 3) root dysfunction, and 4) hot-weather Pythium foliar blight. Pythium hyphae grow rapidly under hot conditions and oftentimes can be seen in morning dews on diseased leaf tissue. Because of this rapid growth and spore release in high temperatures infections can be quick and severe on
turfgrass.

NOTE: Pythium is a spot disease. If you notice large irregular dead patches in your turf without having seen spots first, the problem in NOT Pythium. Pythium blight follows drainage patterns and it can be spread by equipment; hence, it often appears in streaks.
Conditions favouring disease development are wet, humid, cloudy, rainy weather when dew periods are long (greater than 14 hours) with high (26°C to 32°C) temperatures. Late afternoon rain during these hot, humid periods further favour disease development and may be responsible for rapid spread of the pathogen.

Also, Pythium is primarily found on poorly drained soils with pH greater than 7.0, and is increased by hig

h nitrogen fertility.
The Pythium fungus overwinters in soil and plant debris. Due to its spore structure, water is very important to the spread of this pathogen across turfgrass (Pythium is considered a "water mold") Oospores, resistant reproductive fungal structures (Image
2), release motile zoospores which can swim in films of water and spread the disease from one area to another.

Its spread is associated with water movement. When run-off drains through symptomatic turf, the surface water can transport spores. Also, the fungus is readily spread by equipment after affected areas are mowed while wet.

Cultural Control Options

• Modifying the environment may help reduce the severity of Pythium blight.
• Water management and proper drainage to avoid waterlogged root zones during summer are especially important.
• Selective pruning of trees and shrubs will help circulate air and dry turfgrass surfaces, effectively limiting the duration of the dew period.
• Avoiding conditions that produce excessive nitrogen fertility during midsummer will reduce vulnerability to Pythium outbreaks.
• Because of the pathogen’s survival and spread characteristics, Pythium outbreaks normally occur in the same “problem” areas each year as extreme weather conditions prevail.
• Delay mowing in those areas until surfaces are dry.

Chemical control
A number of options are available for Pythium control.
• A useful hint is to apply fungicides past the green onto the collar to provide an extra buffer zone of greens protection from Pythium that may be outside of the green
• When using fosetyl-Al research suggests that two or more consecutive applications of this fungicide are necessary for good control under severe disease pressure. Additionally, Phosphite/phosphonate materials like fosetyl-Al (e.g. Signature) should only be applied to the plant surface. If watered-in, it turns out the soil may change their protective chemistry.

Active ingredient	% Active	Product name	Relative efficacy		Chemical Group
			Preventative	Curative
Mefenoxam	240g/L	Subdue Maxx	+++	++	D
Propamocarb	600g/L	Banol, Proplant	++	+	Y
Azoxystrobin	95g/L	Heritage Maxx	++	+++	K
Terrazole	350g/kg	Terrazole	+	+	X
Thiram	800g/kg	Thiram	+	+	Y
Fosetyl aluminium	800g/kg	Signature	+++	++	Y
Potassium phosphite*	755g/L	Alude, Resist	+++	++	Y
+++ provides greatest efficacy under disease-favourable conditions ++ good management tool under moderate to low disease pressure + This is not a stand alone product for Pythium control. However, when applied preventatively as a tank mix with for example mefenoxam or propamocarb this can significantly improve levels of control and turf quality. * This is not registered in Australia for Pythium sp control in turf

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