Pythium blight is easy to recognize on turf, but the fungus is better disguised in the roots.
When the thermometer is on the rise and moisture is in the air, superintendents cultivating cool-season grasses need to keep an eye out for Pythium.
Peter Landschoot, Ph.D., Professor of Turfgrass Science in the Department of Crop and Soil Sciences at Penn State has been at the university for 23 years – he’s seen Pythium from all angles.
“Around here, Pythium blight can sneak up on us anytime from June to early September,” he said. “I’ve diagnosed it on all cool-season grasses, from bentgrass to fine fescues.”
According to Landschoot, superintendents typically have areas on their courses they scout and monitor, generally wet, low-lying spots. When hot, humid weather is forecast, they make preventive applications with Stellar, Subdue, Banol or Segway - fungicides with both preventive and early curative properties.
“Over the past several years, many superintendents have been making preventative applications with less-expensive phosphite fungicides, which I believe are helping to keep Pythium suppressed,” Landschoot said. “Phosphites are effective preventative fungicides provided the appropriate rates are used, but are not considered to be useful as curative applications. Phosphites also can be translocated to roots, where they can protect plants against Pythium root rot. Vigilance and local knowledge are the key to preventing large outbreaks.”
Even though Pythium can be easy to notice in the field with dense mycelium in early morning and rapid blighting associated with wet areas and drainage patterns (though a lab diagnosis is always recommended) – Pythium-related root problems are a different story.
“There are no characteristic symptoms and you can’t see the fungal structures (mycelium, oospores and sporangia) that are needed for a diagnosis,” Landschoot said. “Even when I’m looking at roots under a microscope, I have a hard time determining if the Pythium present is actually causing disease (some species are more pathogenic than others and you can almost always find Pythium on root tissue - even on apparently healthy roots of healthy plants. It’s really a judgment call.”
As for the potential damage, it can vary depending on location. According to Landschoot, Pythium blight usually occurs once or twice in the summer around central and western Pennsylvania, but going south into Maryland and Virginia, it becomes progressively more severe on cool-season grasses.
The first step in battling Pythium takes place before the problem is spotted.
“Vigilance and preventative fungicide applications when hot, humid conditions are forecast,” Landschoot recommended. “This is one disease where preventative applications are necessary.”
As for seeing results, he said superintendents should see results “within a day or two” when using fungicides that possess good knock-down characteristics.
In the Pacific Northwest, Brian McDonald, a research assistant at Oregon State University, said his region does not have the high temperatures and humidity to get "normal" Pythium (as their temperatures rise, humidity goes down), but there have been superintendents reportedly having Pythium problems over the last several years.
“The difficulty is in the diagnosis,” McDonald said. “Since every sample has Pythium, how does one determine that it is the cause of the disease?
“When there are turf problems creating thin turf and nothing else is found, Pythium is the fallback cause,” he added. “Since the temperature and humidity are not in the range for ‘normal’ Pythium, the cause becomes, ‘cool-weather Pythium’ or Pythium root dysfunction.”
For superintendents in the Pacific Northwest, McDonald suggests other options when thinking Pythium has been found.
“Generally, loss of turf in the Pacific Northwest in cool weather comes down to a few factors: too little sun, too much water (a.k.a. poor drainage) and too much wear,” he said. “Sometimes too little nitrogen is also a factor. Remove the trees, improve the drainage and the ‘Pythium problems’ go away.”