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Significance

Historical significance

Pythium blight, also referred to as "spot blight", "grease spot", or "cottony blight", was first reported in the 1930s, but the disease was not recognized as a problem in some parts of the U.S. until 1954. Pythium blight was initially thought to be a disease of only golf course turf, however, the disease is now recognized as a problem on lawns and athletic fields as well. The disease has been detected on warm- and cool-season turfgrass species in the United States, Canada, Germany, France, and Japan.

The first fungicides used for the control of Pythium diseases included inorganic mercury, captan, dichlone, cycloheximide, and organic mercury compounds. These chemicals only provided limited control of Pythium blight. In 1979, metalaxyl was the first systemic fungicide registered in the U.S for the specific purpose of controlling diseases caused by Pythium, Phytophthora spp., and downy mildew pathogens (oomycetes). This included the specific use for controlling Pythium blight on turfgrasses. In 1983, metalaxyl-resistant populations of P. aphanidermatum were detected in creeping bentgrass samples in Pennsylvania. The samples were from golf courses that had used metalaxyl extensively to control Pythium blight over a period of three years. More recently, isolates of P. ultimum from greenhouse-grown ornamentals and turfgrass plants have been found to exhibit resistance to mefenoxam (another fungicide in the same chemical group) in laboratory assays.