Postharvest diseases of fruits and vegetables
Stored produce is subject to a variety of rots and decay caused by fungi or bacteria. These organisms may cause soft spots or light brown lesions on fruits and vegetables. Fungal growth, in a variety of colors, may also be apparent on the surface of infected produce. In time, the entire fruit or vegetable can become dry and mummified, or, under moist conditions, a soft, wet mass.
Postharvest diseases may start before or after harvesting. Plants or fruits infected in the field may not develop symptoms until stored. Once in storage, infections continue to develop on the fruits and vegetables. Wounds, cuts, or bruises caused during harvesting are common entry points for bacteria and fungi. Penetration can also occur during storage through natural openings, such as lenticels, or directly through the cuticle and epidermis.
Spread of the infection usually requires the presence of warm temperatures and high moisture, although some storage rots can continue to develop at low temperatures. Penicillium, a fungus which causes blue and green mold on fruits, can continue to grow slowly even at temperatures near freezing. Once produce is infected, the disease can spread to healthy produce by direct contact. Insects can also be involved in spreading disease. Fruit flies, attracted to fruits and vegetables infected with "sour rot" carry spores of the fungus Geotrichum from infected produce to healthy produce.
To prevent postharvest diseases, monitor and manage diseases during the growing season. Stake tomatoes to keep fruits from contacting the soil. Pick fruits and vegetables during cool, dry weather and avoid bruising or wounding them. Follow recommended procedures for harvesting and storing specific fruits and vegetables (see University of Minnesota Extension publications Harvesting and Storing Home Garden Vegetables, Growing Stone Fruits in Minnesota Home Gardens, and Growing Apples and Pears in Minnesota). Any diseased fruits or vegetables in storage should be removed when they are discovered.
Agrios, George N. 1978. Plant Pathology, Second Edition. Academic Press, Inc., Orlando, Florida. 703 pp.
Everett, Thomas N. 1981. Onions, page 2392 In: The New York Botanical Garden Illustrated Encyclopedia of Horticulture. Volume 7. Garland Publishing, Inc.
Crockett, James Underwood. 1972. Vegetables and Fruits. 160 pp In: The Time-Life Encyclopedia of Gardening. Time, Inc.
Macnab, Alan A. and Sherf, Arden F. 1986. Vegetable Diseases and Their Control, Second Edition. John Wiley & Sons, Inc, New York. 728 pp.
Chad Behrendt, Crystal Floyd