Postharvest Diseases

Introduction

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. The upcoming revision of the Defects & Disorders Guide may include additional disease symptoms including any new pathogens. To navigate directly to the pest damage of interest use the links below this text block.  The card images shown on this site are slightly modified from their original form to accommodate web formatting. Any reproduction of the card images or content without permission is in violation of WSU Copyright policies.

Blue mold   Gray mold   Speck rot   Sphaeropsis rot   Mucor rot    Powdery mildew   Bull’s Eye rot   Symptom table


Blue mold

Blue mold (primarily Penicillium expansum) is a very common post-harvest 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 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.


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 at a 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.


Speck rot

Speck rot (Phacidiopycnis washingtonensis) is a postharvest disease of apples. Fruit infection originates in the orchard. The source of the inoculum comes from dead or diseased plant tissue of the ‘Manchurian’ crabapple pollinizers in affected orchards. The fungus produces small black dots (fruiting bodies = pycnidia) on ‘Manchurian’ twigs, tree branches and crabapple fruit. Fruiting bodies contain millions of infective spores that can be spread by rain, irrigation or over-tree cooling to nearby apple trees and fruit. Although apple fruit infection occurs in the orchard, fruit rot symptoms develop during storage or at the market.
The cankers and twig dieback caused by P. washingtonensis are not common on apple trees in commercial apple orchards in Washington State, but the ‘Manchurian’ crabapple pollinizer trees are highly susceptible. Detailed pruning of this pollinizer is strongly recommended to significantly reduce the infective potential in commercial orchards.

Postharvest Fruit Syptoms Speck rot symptoms can occur as either stem-end rot (Fig. 1), as calyx-end rot (Fig. 2) or as both. The affected fruit tissue is spongy to firm, which is not differentiable from gray mold and not readily separable from the healthy tissue. The color of the decayed areas varies from light brown to dark brown or occassionally black. Speck rot is so named because of the brown to black specks with white to light tan centers that may appear around the lenticels, especially on red apple cultivars.

Figure 1. Stem-end rot symptoms on a Red Delicious apple after storage.
Figure 2. Calyx-end rot symptoms on a Red Delicious apple after storage.


Sphaeropsis rot

Sphaeropsis rot (Sphaeropsis pyriputrescens)  is a newly reported post-harvest disease of apples and pears. First discovered in D’Angou 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; strong distinct “bandage-like” odor commonly associated with Sphaeropsis rot, particularly when fruit is cut.


Mucor rot

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

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.


Bull’s Eye rot

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