Summary:
Monilinia oxycocci produces a reddish brown cup, disc, or reflexed cup, with a long thin stem, on overwintered mummified cranberries (Vaccinium macrocarpon). Ascospores infect cranberry shoots and about 3-4 weeks later conidia start to form on the shoots. The conidia disperse, grow to penetrate the ovaries of the flowers, and thereby infect the berries. Young infected cranberry shoots show "tip blight" symptoms: "shriveled shoot tips resemble a shepherd''s crook and a tan discoloration spreads from the tip of the shoot down the stem and into leaves"; "To distinguish cottonball tip blight from other shoot diebacks, check the leaves for tan V-shaped or U-shaped lesions centered on the leaf midvein"; "Another indicator is the presence of masses of white, powdery spores (conidia) that appear on diseased shoots just before and during bloom"; "Cottonball tip blight is often inconspicuous and can easily be overlooked"; "Immature diseased berries show no external symptoms, but are filled with the white, cotton-like fungus"; "Healthy berries turn red as they mature; diseased berries may acquire a red blush but are generally yellowish with tan stripes or blotches". (McManus). The distribution is "where the cranberry is cultivated" (Seaver). McManus(1) writes that cottonball, a disease caused by this fungus, fills berries with a cotton-like fungus that makes them unmarketable. It is an economically important disease on many cranberry marshes in Wisconsin. Typically, 2 to 10% of the fruit in diseased beds is infected; if left unchecked the amount can exceed 40%. Cottonball also occurs in the Pacific Northwest and southeastern Canada but losses in those areas have generally been minor.

Microscopic:
spores 12-14 x 6 microns, elliptic; asci reaching 150 x 5-6 microns, 8-spored, clavate, (Seaver), 4 large spores 9.5-14.5 x 5.5-8.5 microns, abortive spores 6-10 x 4-5 microns; conidia 14.5-25 x 9.5-15 microns, oval, "in chains with 3-6 microns long disjunctors", (Hansen)

Notes:
The online Pacific Northwest Plant Disease Management Handbook, accessed December 22, 2013, says that this disease was a problem in WA during the 1920s and 1930s but is rarely found now, except in BC where it is still considered an economic problem. Monilinia oxycocci also occurs in Europe including Denmark, Norway, Sweden, and Finland (Hansen), as well as WI as mentioned above (McManus).

Synonyms and Alternate Names:
Plicatura crispa (Pers.: Fr.) Rea
Trogia crispa (Pers.) Fr.