Controlling Postharvest Diseases of 

 Apples and Pears 



Editors' Note: The following information has been taken from a series of articles in the 

 December, 1989, issue of the Postharvest Pomology Newsletter, published by the Washing- 

 ton State University and the U.S. Department of Agriculture, Wenatchee, Washington. 



Postharvest Diseases and Disorders of 

 Apples and Pears 



Several of the more common postharvest diseases 

 and disorders of apples and pears are described below. 



Gray Mold (Botrytis cinerea). Botrytis rot is a com- 

 mon 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 unpro- 

 tected fruit wounds or susceptible tissue. These ini- 

 tially 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 Mold (Penicillium expansion). Blue mold 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, par- 

 ticularly those near bruises. Late in the storage season 

 when fruit has been weakened by ripening and aging, 

 most cultivars 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 tempera- 

 ture 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. Like- 

 wise, delays in cooling fruit after harvest also increase 

 the chance of blue mold. Careful fruit handling, pack- 

 inghouse sanitation, prompt fruit cooling, and proper 

 temperature management during the storage period 

 are keys to reducing blue mold. 



Alternaria Rot (Alternaria alternata). Alternaria rot 

 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 (Pezicula malicortids). Bull's eye rot 

 infections occur in the orchard as well as after harvest, 

 becoming established in the fruit at any stage of devel- 

 opment 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. The spores that infect fruit come from can- 

 kers 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 in- 

 jured 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 Rot (Mucor piriformis). Mucor 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). Side rot can affect 

 both apples and pears but is most severe on pears, 

 particularly Bosc. Similar symptoms can be caused by 

 the fungus Cladosporium herbarum. However, since 

 Cladosporium is sensitive to commonly used posthar- 

 vest 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 con- 

 taminated with orchard soil. 



Practices to Minimize Postharvest Decay of 

 Apples and Pears 



Preharvest 



•Maintain good weed control, and keep grass mowed. 

 A drier orchard microclimate will reduce Mucor rot, 

 Coprinus rot, and scab. 



Fruit Notes, Summer, 1990 



17 



