Verdure: Is it Pythium?

Are we spreading Pythium inoculum when we irrigate?


Filed to: Verdure, Disease

Pythium disease on a golf course

The rock band Deep Purple released “Smoke on the Water” in 1972, and just reading that may trigger the iconic four-note riff to play in your mind. Pythium and water, and the destructive nature of Pythium disease on golf courses, is not something to sing about.

Back in the day, the mere mention of the word Pythium would strike fear into the bravest golf course superintendents. Prior to the availability of reliable and effective fungicides, a Pythium blight outbreak would mean turfgrass devastation and death literally overnight. Unfortunately, Pythium became known as the “résumé disease,” because a Pythium epidemic would result in the golf course superintendent looking for a new job. Although cultural and chemical practices have greatly improved, Pythium can still wreak havoc on the golf course.

Several Pythium species cause foliar, root rot and root dysfunction diseases of turfgrasses, and all turfgrasses are susceptible to infection by Pythium species. Cool-season turfgrasses are especially vulnerable during hot, humid weather conditions along with excessive soil moisture. Warm-season turfgrasses are more susceptible during cool or cold weather, along with periods of low light intensity and also high soil moisture, and often Pythium disease symptoms may resemble various leaf blights.

Incidentally, Pythium used to be classified as a fungus, but has been reclassified into the newly proposed biological kingdom of chromista. Pythium is still considered a water mold and listed as an oomycete, and it is still a virulent and destructive plant pathogen, but evidently the evolutionary biologists wanted these water molds to have their own kingdom.

Recently, research was conducted at the University of Missouri (Columbia) for the purpose of examining irrigation systems as a potential mechanism of disseminating Pythium. In other words, Pythium likes water, so are we spreading Pythium inoculum when we irrigate? Irrigation water was collected from eight golf courses in Missouri and two in Kansas during the spring, summer and autumn over two consecutive years.

Water samples were collected on putting greens from irrigation cycles during early morning to midday. Water samples were also obtained directly from irrigation sprinklers and from water sources (i.e., municipal, surface water, well) at the golf courses.

In the laboratory, tedious but highly accurate techniques were employed to examine the water samples for detection of Pythium zoospores, and for attempting to grow Pythium mycelium in culture. Identification of Pythium species was achieved through molecular DNA extraction and phylogenetics. In other words, the irrigation water samples were thoroughly scrutinized from 72 replicates of each water sampling source, 72 replications for each laboratory detection method, and 36 replicates during each sampling period.

The results of this detailed study showed that some Pythium species and Pythium-related species can be detected in golf course irrigation water unless treated municipal water is used as an irrigation source, or if water sterilization practices are used, such as an ultraviolet light treatment. Golf course superintendents should not panic about their irrigation water source as an incubator for growing Pythium zoospores but remain focused on irrigating to promote the growth and development of turfgrass and produce the best playing surface as possible. Also from this study, there were no correlations with irrigation water analysis (i.e., temperature, electrical conductivity, nutrient content) and Pythium species detection.

With a Pythium outbreak, once you see any foliar blighting, most likely all affected turfgrass areas are dead or soon will be. It is important to remember that the pathogen is a water mold that will travel or “run” wherever water moves and carries its mycelial fragments and zoospores. Therefore, Pythium disease is typically more severe where surface water collects or puddles and where the pathogen is carried on equipment tires or rollers, thus producing peculiar, straight lines of dead turf.

Irrigation water management, maintaining uniform and consistent soil moisture, and good surface and subsurface drainage are all important components of a sustainable Pythium disease management program, especially during those environmental conditions that favor the growth and development of the Pythium species. With your turfgrass management practices optimized, you can enjoy listening to some relaxing music this weekend.

Source: Rushford, C.A., R.L. North and G.L. Miller. 2022. Detection of Pythium spp. in golf course irrigation systems. Plant Disease 106:46-56 (

Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 21-year member of GCSAA.

Filed to: Verdure, Disease

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