Photograph 1. White leaf symptoms on a Kentucky bluegrass/perennial ryegrass turf. The white leaf blades are caused by a phytoplasma that degrades the chlorophyll.
The pathogen is a phytoplasma which is classified in a group of similar prokaryotic organisms known as mollicute. The difference between normal bacteria and mollicutes, like phytoplasma, is no cell wall is present with mollicute organisms. Phytoplasma appear to be transmitted through leafhoppers which deposit the pathogen in the plants phloem.
The disease is rare and often disappears without causing any plant injury or death. There is no known control for the disease.
Photograph credit: Paul B. Latshaw.