Postharvest Diseases and Disorders of Apples and Pears
Gray mold (Botrytis cinerea)is a common decay of apples and pears. This fungus enters through punctures and wounds; therefore, minimizing fruit injury will reduce the amount of decay from this fungus. The source of Botrytis spores is the orchard. The fungus grows and sporulates abundantly on dead and dying plant material found in orchard cover crops, especially during cool, moist weather. Infection can occur in the orchard or at any time in the handling process that the spores come in contact with unprotected fruit wounds or susceptible tissue (e.g., Anjou pear stems). These initially rotted fruits spread the disease to fruit in contact with them to produce nests or pockets of decaying fruit. The disease is often called nest or cluster rot.
Blue MoldBlue mold (Penicillium expansum) is a common destructive rot found on fruits in storage and at the market. It is generally considered a wound parasite, but it can penetrate through lenticels, particularly those near bruises. Late in the storage season when fruit has been weakened by ripening and aging, most varieties are susceptible to lenticel infection. The infection can start when pears or apples are handled carelessly during the packing process. Environmental conditions such as moisture, ventilation and temperature directly influence the development of decay. The fungus grows well at humidities normally found in cold storage. Poor ventilation around storage containers leads to increased moisture around the fruit and slower cooling times, increasing the risk of infection. Likewise, delays in cooling fruit after harvest also increase the chance of blue mold. Careful fruit handling, packinghouse sanitation, prompt fruit cooling and proper temperature management during the storage period are keys to reducing blue mold.
Alternaria rot (Alternaria alternata) may occur on apples and pears in any production stage. This fungus lives on dead and decaying plant tissue in the orchard, and its spores contaminate fruit in the orchard or during the handling process. The amount of decay depends on the condition of the fruit. Infection usually occurs through breaks in the skin or other weakened areas caused by sunburn, bruising, chemical injury or scald.
Bull's Eye Rot
Bull's eye rot (Pezicula malicorticis) infections occur in the orchard as well as after harvest, becoming established in the fruits at any stage of development from petal-fall onward. The rot usually begins at open lenticels and develops slowly at cold storage temperatures. The rot does not spread from one fruit to another. All varieties are susceptible, but Golden Delicious, Newtown and Rome Beauty are among the most susceptible. The spores that infect fruit come from cankers on branches of apple trees in the orchard. In the tree, this disease is called perennial canker. These cankers often start around old pruning cuts and are associated with woolly aphid feeding. Cankers are not produced on pear trees, but the fungus colonizes injured or dead bark. Preharvest fungicides will help prevent bull's eye rot. Harvested fruit should not be left in the orchard during rainy weather.
Mucor (Mucor piriformis) is a soil-borne fungus that grows well even at cold temperatures. The fungus grows in fallen fruit on the orchard floor so, any practice that reduces rotting fruit in the orchard or movement of spore-laden soil, into the packinghouse on bins will help to reduce Mucor problems. There is no effective fungicide registered for control of Mucor.
Side rot (Phialophora malorum) can affect both apples and pears but is most severe on pears, particularly the Bosc variety. Similar symptoms can be caused by the fungus Cladosporium herbarum. However, since Cladosporium is sensitive to commonly used postharvest fungicides and Phialophora is not, the latter has been the major cause of side rot losses. Spores of this fungus also enter the packinghouse on bins or fruit contaminated with orchard soil.
Coprinus RotCoprinus rot (Coprinus psychromorbidus) has been identified throughout the Pacific Northwest and is often mistaken for bull's eye rot. Fruit infection occurs during the last month before harvest. This fungus appears as a white, "cobwebby" growth on the surface of infected fruit and will create nest or cluster rot like gray mold.
Scald is a physiological disorders of apples and Anjou pears characterized by a brown discoloration of the skin which occurs during storage. This browning is thought to be caused by the production of naturally occurring toxic compounds in the fruit peel. Early harvested fruit is at greatest risk. While the most reliable way to reduce scald is use of postharvest anti-oxidant drenches or sprays, researchers are looking at other ways of improving scald control including prediction of its occurrence and severity and use of controlled atmosphere storage.
Mike Willett(1), Gene Kupferman(2), Rodney Roberts(3), Robert Spotts(4), Dave Sugar(5), Gary Apel(6), Hugh W. Ewart and Bill Bryant (7)
(1)WSU Cooperative Extension Agent, Yakima, WA; (2)Postharvest Specialist, WSU TFREC, Wenatchee, WA; (3)USDA Pland Pathologist, Tree Fruit Research Lab, Wenatchee, WA; (4)OSU Plant Pathologist, Mid-Columbia Research and Extension Center, Hood River, OR; (5)OSU Plant Pathologist, Southern Oregon Experiment Station, Medford, OR; (6)Michelsen Packaging Company, Yakima, WA; (7)Northwest Horticultural Council, Yakima, WA
Post Harvest Pomology Newsletter, 7(3): 4-5