Plant Disease Management Handbook

Cause Three viruses generally considered as "latent" in apple are apple stem grooving virus (ASGV), apple stem pitting virus (ASPV), and apple chlorotic leaf spot virus (ACLSV) all of which are not too important in commercial apple production. ASGV causes apple decline on Virginia crabapple, ASPV causes Apple Spy 227 epinasty and Spy decline while ACLSV causes Apple chlorotic leafspot on many crabapple cultivars (also called apple top-working disease in Japan).

Apple stem grooving virus on indicator host Malus micromalus.

Image from USDA- APHIS Plant Germplasm Quarantine Program.

Apple stem pitting virus on indicator host Spy apple.

Image from USDA- APHIS Plant Germplasm Quarantine Program.

Image related to Apple (Malus spp.)-Latent Virus Diseases

Apple chlorotic leafspot virus. Photo taken at the Sidney quarantine station on indicator cultivar (file labeled Russian Apple).

B.C. Ministry of Agriculture and Lands (Jesperson)

Apple chlorotic leafspot virus on indicator host Russian apple.

Image from USDA- APHIS Plant Germplasm Quarantine Program.

See:

Apple (Malus spp.) - Latent Virus Diseases

Apple fruit with green crinkle develop deep depressions and distortions that increase in severity as the fruit matures giving them a lumpy appearance.

OSU Plant Clinic, 2021.

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Prune and Plum (Prunus spp.) - Russeting

Apple on the left has russet which can be due to many things including early infection by powdery mildew.

Jay W. Pscheidt, 2012.

Image related to Apple (Malus spp.)-Fruit Russeting

Russet on these 'Rome' apples is due to application of insecticidal soap.

Jay W. Pscheidt, 1995.

Cork tissue forms on the outer surface of the fruit.

Photo by Ralph S. Byther

Russet due to powdery mildew on an unsprayed 'Golden Delicious' tree.

OSU Extension Plant Pathology Collection, 1977.

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Apple (Malus spp.) - Crown and Collar Rot

Pear (Pyrus spp.) - Storage Rots

Note the discoloration at the base of this 'Golden Delicious' fruit.

Photo by Iain MacSwann, 1968.

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Cherry (Prunus spp.) - Rasp Leaf

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Pear (Pyrus spp.) - Fire Blight

Apple Cultivar Susceptibility

Young flowers/fruit 2 weeks after infection, note droplets of bacterial ooze on the fruit stems.

Tianna DuPont, WSU Extension, 2016.

Infected Gala apple shoot beginning to wilt and dieback from fire blight.

Tianna DuPont, WSU Extension, 2017.

When vigorously growing shoots die from fire blight the tip turns down to form the Shepard's crook symptom.

Tianna DuPont, WSU Extension, 2019.

Canker forming on small branch from fire blight infected spur. Oozing canker can be a source for secondary infection.

Tianna DuPont, WSU Extension, 2019.

Image related to Apple (Malus spp.)-Fire Blight

The classic shepherd's crook symptom where the tip of the shoot turns down when it dies."

Photo by Jay W. Pscheidt, 1997.

A hold-over canker on main trunk. This canker will remain here and provide inoculum for next year unless removed."

Photo by Jay Pscheidt, 1995.

Cause Apple dead spur is caused by a graft-transmissible agent that apparently originated in the Western United States. The pathogen has not been identified, although apple stem pitting virus, apple stem grooving virus, and apple chlorotic leaf spot virus have been detected in diseased material. The only known means of disease spread is through the use of infected propagation material.

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Peach (Prunus persica) - Cytospora Canker

Image related to Apple (Malus spp.)-Cytospora Canker

Note the discolored areas on this 'Honey Crisp' branch.

OSU Plant Clinic collection, 2012.

Note margin between healthy wood near top of image and diseased tissue.

OSU Plant Clinic Collection, 2016.

This Honeycrisp apple had Cytospora canker (not fire blight!).

Oregon State University Plant Clinic image, 2020.

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Cherry (Prunus spp.) - Crown Gall

Note: In the Pacific Northwest, Malling 7 is considered the most susceptible apple rootstock to Rhizobium rhizogenes (formerly Agrobacterium tumefaciens), followed by Malling 9 and 26.

Image related to Apple (Malus spp.)-Crown Gall

Note galled areas on the rootstock of EMLA 29.

OSU Plant Clinic collection, 2012.

Cuttings with crown gall and not normal callose growth.

Melodie Putnam, 2010.

Unknown galling problem on the 'Mark' rootstock. Seen when new trees begin to fruit.

Photo by Jay Pscheidt, 1993.

See:

Apple (Malus spp.) - Fruit Rot, Phytophthora

A shallow cut with a pocket knife shows healthy white to greenish tissue above and diseased dry brown necrotic tissue below.

OSU Plant Clinic Image, 2016.

Image related to Apple (Malus spp.)-Crown and Collar Rot

Even without cutting into the tissue one can see the slightly sunken necrotic area near the base of this tree.

OSU Plant Clinic collection, 2012.

Discoloration of the vascular cambium of this 'Honeycrisp' apple above the graft line would be referred to as collar rot.

OSU Plant Clinic Image, 2014.

Soil has been removed to expose a dead, infected, discolored root.

Photo by Jay Pscheidt, 1991.

Crown rot can also occur on young trees. The outer bark has been cut away to expose the vascular cambium where healthy tissue above is a normal light green while the diseased tissue is a dark cinnamon brown below.

Phil Hamm, 1996.