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Diseases & Disorders

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A disease can be broadly defined as any departure from the normal condition of plants or plant parts which detracts from their appearance, interferes with their usefulness or reduces their value. Under this definition are included abnormalities caused by fungi (parasitic diseases), and functional disorders (physiological disorders).

In the orchard, diseases can be caused by fungi, bacteria, viruses or mycoplasmas. Postharvest parasitic diseases of apples in the Pacific Northwest are predominately caused by fungi. Disease prevention is essential to preserving fruit quality. Prevention begins in the orchard and includes using properly timed fungicide sprays, practicing orchard sanitation,  harvesting at optimum maturity, and using methods that minimize the bruising of fruit.


The production of apples is a complex process involving orchard management, storage, and marketing phases.  Technology makes the long-term storage of fruit possible, and in Washington State, apples can be stored for up to 12 months. Postharvest diseases can be a limiting factor to long-term storage though, with fruit decay and repacking due to disease costing the fruit industry millions of dollars in losses each year. Some Postharvest diseases originate from infection in the orchard (Sphaeropsis rot caused by Sphaeropsis pyriputrescens, Phacidiopycnis rot caused by Potebniamyces pyri, and Bull’s eye rot caused by Neofabraea spp.); and some are associated with postharvest handling processes (Blue mold caused by Penicillium spp., mainly P. expansum, Gray Mold (Botrytis cinerea), and Mucor rot caused by Mucor piriformis).   Postharvest parasitic diseases of apples in the Pacific Northwest are predominantly caused by fungi.

The control of postharvest decay begins in the orchard with orchard floor sanitation, fungicide applications,  and insect control, and continues with careful fruit handling practices before and during cold storage until fruit are sold.  Strategies to control fungal diseases of apple are of major concern to warehouse managers.  WSU researchers are conducting studies on postharvest diseases in two phases: 1) fruit decay in storage bins before packing and 2) fruit decay after packing.  Accurate diagnosis of postharvest diseases is the first step to implement relevant measures to control the problems. Learn more »  Links to Tree Fruit Market Diseases.

WSU’s postharvest information network is a source for information on apples, and post-harvest practices. Go to the Postharvest Information Network home page.

Cullage Assessment

With a keen eye on the needs of Washington producers selling to the global market, WSU researchers have trainings and information to help industry professionals identify damage and disorders encountered during the cullage assessment phase of the post-harvest process. There are also useful materials for people involved with identification of fruit damage in the orchard. Available materials include visual identification guides, instructions for sampling in the orchard and packinghouse, as well as, quarantine pest and export work plan information. Learn more »




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Postharvest diseases in Pears are generally caused by fungal pathogens that can infect fruit before, during, and after harvest.  Understanding when infection occurs is an essential step for developing and implementing control measures to reduce storage losses due to decay. Fruit that are infected in the orchard will not show symptoms until later in storage.  Dead bark, twigs, and cankers on trees may contain fungal pathogens like Potebniamyces pyri, which causes Phacidiopycnis rot. Growers must begin disease control procedures in the orchard for postharvest diseases of pears that cause decay in storage.  Orchard sanitation and pre-harvest fungicide treatments are important steps in disease control.  Some decay causing organisms infect wounds that occur during the harvest and postharvest handling processes.  Limb rubs, stem punctures and bruises are entryways for fungal spores such as Blue mold, caused by Penicillium spp., mainly P. expansum, and Gray Mold caused by Botrytis cinerea.  Accurate identification of postharvest diseases is the first step in applying appropriate actions for control. See the Postharvest diseases of apples and pears guide here, and the apple postharvest quick identification guide for more information on these diseases.

Harvest maturity is a critical variable in helping prevent storage decay.  Pears harvested on the immature side will scrape easily on the packing line, introducing wounds, which are sites for infection, and fruit harvested late in the maturity range has reduced storage life, and is more susceptible to postharvest diseases. Careful handling of pears at harvest, and preventing wounds is crucial. Packinghouse sanitation is also imperative in the disease control process.  Winter pears such as d’Anjou, are usually packed shortly after harvest in cardboard boxes, and can be stored in CA storage for up to 9 months in Washington State. Decay on packed fruits in the boxes is a major concern for growers and warehouse managers.

Scientists at WSU are working with growers and packinghouse personnel to find better ways to control decay in postharvest fruit.  For information on pears, and postharvest diseases, visit WSU’s postharvest information network.


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Some of the same diseases attack apples, pears and cherries.  Many diseases of cherries  are significantly more serious during seasons in which rain cracking occurs.  Cracks in cherries act like wounds, and are entry points for fungal spores to enter the fruit. Two postharvest diseases unique to cherries are Cladosporium Rot (Cladosporium herbarum) and Rhizopus Rot (Rhizopus spp.).  Spores from these fungi enter the fruit through breaks in the skin, and proceed to decay the fruit. Careful handling, removal of damaged fruit, and rapid cooling are effective methods of decay management for these diseases.

To learn more about postharvest diseases of cherries, and orchard and packinghouse practices, visit the WSU Tree Fruit Research and Extension Center Postharvest Information Network site.


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