Lay the quilt on the lawn overnight where it will get morning sun, leave there until afternoon. If the mildew goes clear through, turn the quilt over and leave out for another day. the chlorophyl in the grass, the sunlight and the overnight dew will get rid of the mildew, even the smell. It may take a few days, depending on size/depth of stain. Sounds wierd, but works on a wide variety of stains.