Penicillium expansum Thom
Blue mold rot is one of the most troublesome postharvest diseases of pears. It occurs on all varieties of pears throughout the world. The affected tissues, like those of blue mold rot of apples, are soft and watery, and are easily separated from the adjacent healthy flesh. Three forms of the disease occur: cheek rot, stem and neck rot, and pinhole rot.
Cheek rot, as the name implies, develops on the cheek of the fruits. It occurs on all varieties of pears, and is the form of the disease most frequently found on the market. Infection occurs through cuts, abrasions, punctures, and other breaks in the skin. The rot spots are circular, and vary from less than 1/4 inch to more than 2 inches in diameter (middle photo).
Stem and neck rot is a form of the disease that develops from stem infections in fleshy-stemmed varieties such as Anjou and Comice (top photo). Losses from this disease have increased since the storage season for pears has been extended through the use of polyethylene box liners. The fungus grows down through the stem which remains firm, but darkens. It spreads by way of the vascular tissues into the neck of the fruits where the flesh becomes soft and watery. The amount of decay that develops on a single fruit depends on the length of the storage period. It may involve only the stem, the stem and a small area at its base, or the entire upper half of the fruit. The high humidity that prevails within polyethylene box liners favors the development of white to bluish-green fungal masses of spores on the surface of affected tissues.
Pinhole rot is a form of the disease that occurs mainly on Winter Nelis, a variety with large prominent lenticels. It first appears as numerous minute spots of decay scattered over the surface of the fruit, with infection apparently taking place at the lenticels. As the disease progresses the spots increase in size, finally coalescing to decompose the entire fruit.
Sodium orthophenylphenate used as a fungicidal wash (See Pear Gray Mold Rot) controls pinhole and cheek rots, but not stem and neck rot. Captan as a fungicidal wash, however, is effective against cheek and stem and neck rots. For most effective disease control, fungicides are only supplements to careful handling, packinghouse sanitation, prompt cooling, and adequate refrigeration of the fruits.
Pear blue mold rot, at stem end
Pear blue mold rot, at skin puncture
Pear blue mold rot