Pythium Root Rot
Not much is known about the disease cycle of this root-infecting Pythium disease. Pythium root rot is a consistent issue in turf areas that are poorly drained, have high organic matter content or are overwatered. Like Pythium blight, disease symptoms can also occur when extended periods of rainfall result in saturated soil conditions. Pythium root rot may infect over a wide range of temperatures, but symptoms from root impairment will occur most prominently during periods of high temperature stress. Stand symptoms are orange, yellow or dark-colored areas that occur in irregular patterns and may spread in drainage patterns during periods of high rainfall. Individual plants have dark, necrotic crowns and roots with a noticeable reduction in root depth. In Missouri, most issues with this disease are found on putting greens.
Increase surface and subsurface drainage. Do not water excessively when this disease is active. During the spring and fall, core aerify aggressively and dilute organic matter with sand replacement and topdressing. In areas with a history of the disease, fungicides should be applied preventively before forecasted periods of extended rainfall.