What is winterkill?

Winterkill, or winter kill, refers to grass that has been done in by wintry extremes. Grown in the proper climate zones, most lawn grasses snap back after winter, but severe or extended cold weather and lack of insulating snow cover can partly or completely kill off a lawn. Common causes of winterkill include cold desiccation, in which uncovered grasses continue to lose moisture in the cold, and snow mold, which is the collective name for a variety of fungal diseases that cause crusty or fuzzy patches on a lawn.