These are best mowed with a sharp rotary mower. Perennial ryegrasses can be mowed at 1.0-2.5 inches on home lawns. Apply 1.0 to 1.5 lbs. Up in Flagstaff, consider applying a preventative fungicide for snow mold diseases. Snow molds can completely kill the turf during the winter, whether there is snow cover or not.
Snow mold is worse under conditions of freezing and thawing cycles, accompanied by winter rains.
This actually prevents water loss from the leaves, thus avoiding winter desiccation up in Flagstaff and other true high elevation areas. Arizona Board of Regents.