Southern blight
View LargerCaused by Sclerotium rolfsii. In poa/rye rough. Southern California, July, 2008. The disease started at the center of this circular patch (turf has now begun to recover there), and then moved outwards in the direction indicated by the arrow. If you are looking for mature sclerotia, they will be found in the area with the oldest infestation (the center).