Monilinia oxycocci

Monilinia oxycocci (Woronin) Honey, (synonym Sclerotinia oxycocci), common names cranberry cottonball, cranberry hard rot, tip blight, is a fungal infection of large cranberry (Vaccinium macrocarpon) and small cranberry (Vaccinium oxycoccos). The tips of young flowering shoots wilt before they flower. Fruit that forms on the plant can then be infected by the asexual spores traveling through the plant, causing the berries to harden, turn cottony on the inside, and dry out instead of maturing. The berries are filled with a cotton-like fungus and are generally yellowish with tan stripes or blotches at maturity, making them unmarketable. It results in important economic impacts on many cranberry marshes, particularly in Wisconsin.

from Wikipedia