Pythium blight is active on perennial ryegrass and creeping bentgrass where hot humid conditions persist.  The disease is most severe on thatchy and compacted soil sites.  On perennial ryegrass, pythium symptoms are often confused with brown patch. It is difficult to tell the two diseases apart on perennial ryegrass without the help of a diagnostic laboratory. If in doubt send a sample to confirm your diagnosis.  Pythium blight can cause severe problems on creeping bentgrass.  Often times this disease is found in low areas where wet conditions persist.  Interestingly, pythium blight can also appear around small damaged areas like divots.  Preventative fungicide applications are the most effective means for controlling Pythium blight