Answer: I really can't diagnose the problem without seeing it but it sounds suspiciously like slime mold. Slime mold (Physaricum cinereum) first appears as white, yellow or gray puffy or slimy growths on grass blades, forming powdery puffs as they dry. Usually this growth appears in area of the lawn that is moist, shaded, and has poor air circulation. Fortunately, slime molds do not really harm the grass; they feed on decaying organic matter or thatch. They usually disappear as soon as the weather gets drier. However, if the growth is abundant, it may suffocate grass plants and cause turf to thin out. You can control this fungus by simply sweeping it off the grass with a broom or washing it off with a garden hose.
However, it might be snow mold rather than slime mold. Gray snow mold, or Typhula blight (Typhula sp.) is most common on lawns that have been covered by heavy snow throughout the winter. When the snow finally melts in spring, it reveals patches up to 2 feet across covered with white or gray fungus. To repair damaged areas, loosen up matted grass to improve air circulation, and spray a general garden fungicide containing sulfur according to label instructions for turf. Aerate the soil and improve drainage if needed. Avoid overfeeding with nitrogen fertilizer in the fall, and remove thatch if it is more than ? inch thick. Avoid walking on the lawn during the winter, especially if there is snow cover.
Hope this information is helpful and you determine just what the problem might be.
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