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Blue mold

Penicillium expansum Link

Blue mold enters the fruit through wounds, stem-end invasion, or as a core rot (A). Infection is first visible as a soft and sunken, yellow to pale-brown circular lesion on the surface of the fruit. Lesions expand rapidly and can quickly macerate the fruit (B). A diagnostic symptom of this rot is a strong earthy or musty odor and unpleasant taste. If fruit are stored under wet or humid conditions, the fungus produces numerous blue-green tufts of spores on the surface of the fruit (C); sporulation typically does not occur under CA conditions (compare with gray mold).


Common to all fruit-growing regions in eastern North America.

Similar Species

In the absence of sporulation, blue mold can be confused with other postharvest diseases such as gray mold. Gray mold-rotted tissue, however, tends to be firmer than tissue infected with blue mold and does not separate easily from healthy tissue. Unlike blue mold, gray mold-rotted fruits have a relatively pleasant odor rather than a musty odor.


Postharvest applications of fungicides can be useful for preventing infections, but sanitation of picking bins and packinghouses is also essential. Quaternary ammonia sanitizers can be used to clean empty bins and storage rooms. Chlorination or other approved biocides should be used in the packinghouse to control inoculum in dump tanks and flume water. Packinghouse floors should be cleaned daily and all decayed fruit should be removed as soon as possible.

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