Blue mold

Blue mold originates primarily from infection of wounds such as punctures, bruises and limb rubs on the fruit. Blue mold can also originate from infection at the stem of fruit. Stem-end blue mold is commonly seen on d’Anjou pears, but it also occurs on apples such as Red Delicious (Fig. 3). Calyx-end blue mold occurs on Red Delicious apples but is usually associated with fruit that are drenched prior to storage.
The decayed area appears light tan to dark brown. The decayed tissue is soft and watery and the lesion has a very sharp margin between diseased and healthy tissues. Decayed tissue can be readily separated from the healthy tissue, leaving it like a “bowl”. Blue or blue-green spore masses may appear on the decayed area, starting at the infection site. Decayed fruit has an earthy, musty odor. The presence of blue-green spore masses at the decayed area and associated musty odor are the positive diagnostic indication of blue mold. Without the presence of spore masses of blue mold, blue mold can be misdiagnosed as Mucor rot, but a sweet odor is commonly associated with Mucor rot.