Tree Fruit Research & Extension Center

Cullage Assessment & Education

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Quick Identification Guide to Apple Postharvest Defects & Disorders

Postharvest Diseases

The Diseases section of the card set includes all the major fungal diseases found in stored Washington apples. This section also includes a Symptom Comparison Table to help. At a later date more cards may be developed for this section which would include any newly discovered pathogens. For ordering information vist the Additional Information section of the Introduction. The cards shown below are slightly modified to accomodate web formatting. Figures may appear fragmented in some browsers. Please report viewing problems here. Any reproduction of the card images or content without permission is in violation of WSU Copyright policies.


DISEASES: Blue Mold  

Blue mold (primarily Penicillium expansum) is a very common postharvest fungal disease on apples worldwide. This disease is of economic concern to both the fresh-fruit industry and the fruit-processing industry because some strains produce the mycotoxin patulin, which can rise to unacceptable levels affecting the quality of apple juice.

Figure 1: Blue mold originating from infection of wound on fruit; decayed area brown, soft, and watery, with a sharp margin; blue-green spore masses visible.

Figure 2: Blue mold decayed tissue is completely separable from the healthy tissue.

Figure 3: Blue mold originating from infection of wound on a Granny Smith fruit; spore masses formed at the infection site.

Figure 4: Calyx-end blue mold on a Fuji fruit; usually associated with drenched fruit.


DISEASES: Gray Mold  

Gray mold (Botrytis cinerea) is a common post-harvest disease on apples worldwide. This fungus has the ability to spread from decayed fruit to surrounding healthy fruit through fruit-to-fruit contact during storage. Because of this, significant losses as high as 20-60% are not uncommon after an extended period of storage, particularly on fruit that were not treated with fungicides prior to storage.

Figure 1: Gray mold originating from infection at stem or stem bowl; gray spore masses may be visible at the diseased area under high humidity.

Figure 2: Gray mold commonly originating from infection of wounds on the fruit; decayed area brown, spongy to firm; decayed tissue may become soft in very advanced stage.

Figure 3: Gray mold originating from infection of the calyx of a Red Delicious; white to gray mycelium and gray spores may cover the decayed area under high humidity conditions.


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DISEASES: Sphaeropsis Rot  

Sphaeropsis rot (Sphaeropsis pyriputrescens) is a newly reported postharvest disease of apples and pears. First discovered in D’Anjou pears, but was later determined to cause worse problems in apples. In one case, 24% of the apples in bins were rotted by this disease after several months of storage. Sphaeropsis rot has occurred on Red Delicious, Golden Delicious, Fuji, and Granny Smith.

Figure 1: Sphaeropsis rot originating from a stem infection on a Golden Delicious apple; decayed area brown, firm.

Figure 2: Sphaeropsis rot originating from a calyx infection on a Red Delicious fruit.

Figure 3: Sphaeropsis rot originating from a calyx infection on a Fuji apple.

Figure 4: Internal decayed flesh is light tan to brown; a strong distinct “bandagelike” odor is commonly associated with Sphaeropsis rot, particularly when fruit is cut.


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DISEASES: Mucor Rot & Powdery Mildew  

   
 

Mucor rot can cause significant losses of fruit, but is generally not a major problem when good harvest management and water sanitation practices at packing are implemented.

Figure 1: Mucor rot (Mucor piriformis) on a Golden Delicious fruit showing very soft, juicy, decayed tissue with a sharp margin. Mucor rot decay often has a sweet odor.

 

Powdery mildew may be found on apple buds, blossoms,leaves,twigs,and fruit. When fruit are infected,the surface may become russetted or discolored, and sometimes dwarfed. Fruit is most susceptible during the period around petal fall.

Figure 2: Powdery mildew may result in a net-like scarring called russetting.


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DISEASES: Bull's Eye Rot  

Bull's Eye - GD side

Bull’s eye rot occurs on Pacific Northwest apples. In Washington State, Bull’s eye rot is more commonly seen on Golden Delicious, particularly on apples from orchards with perennial canker problems on trees. Bull’s eye rot also occurs in Europe and some other fruit-growing regions.

Figure 1: Bull’s eye rot on a Golden Delicious fruit; lesion is flat to slightly sunken, brown to dark brown with lighter brown to tan in the center, resembling a Bull’s eye.

Figure 2: Multiple Bull’s eye rot lesions on a Golden Delicious fruit.

Figure 3: Bull’s eye rot originating from infection at the calyx end of a Golden Delicious fruit.

Figure 4: Bull’s eye rot originating from infection at the stem-bowl area of a Golden Delicious fruit.

Bull's Eye - GD multi
Bull's Eye - stem Bull's Eye - calyx

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Diseases: Symptom Comparison Table  

Symptoms Blue Mold Gray Mold Sphaeropsis Rot Mucor Rot
Texture Soft, watery; lesion with a sharp margin; decayed tissue completely separable from the healthy tissue, leaving it like a “bowl” Spongy or firm; decayed tissue not separable from the healthy tissue Firm Very soft; juicy
Decay Color Light tan to dark brown Light brown to dark brown Brown to dark brown, advanced decay area may turn black Light brown to brown
Signs of Pathogen White mycelia and blue or blue-green spore masses; sporulation often starts at the infection sites (wounds) Fluffy white to gray mycelia; sporulation under high humidity; gray to brown spore masses; black sclerotia may form White mycelia under high humidity; advanced stage: pycnidia may form on decayed fruit Gray mycelium with dark sporangia
Internal Color Brown Light brown to brown Brown; decay advances along the vascular tissue; decay turning it brown Light brown to brown
Odor Earthy, musty Generally not detectable Strong distinct “bandagelike” odor Sweet

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