Plant Disease Management Handbook

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Apple (Malus spp.) - Scab

Pear Cultivar Susceptibility

Dark spots are scab lesions while lighter small spots are just lenticels.

Neil Bell, 2014.

Scab can be clearly seen on the leaves and fruit.

Photo by Wayne Roberts, 1979. (Jeff Olsen collection)

Spots are frequently observed on the underside of leaves as diffuse dark spots. These are on the cultivar Bartlett.

Jay W. Pscheidt, 2013.

Twig lesions near base of petioles and into wood.

Rachel Elkins.

Numerous twig lesions along this year old stem.

Rachel Elkins.

Stem lesions are very troublesome as an overwintering site and need to be removed if observed.

Rachel Elkins.

Note the sunken, dark lesions on this fruit.

Photo by Jay W. Pscheidt, 1992.

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Apple (Malus spp.) - Replant Disease

Cause Pseudomonas syringae pv. syringae, a bacterium. Rain and low temperatures, especially frost-inducing temperatures during bloom, increase incidence of blossom infection. Although the bacteria survive on the outside of the plant they must get inside and multiply in the space between plant cells (apoplast) to cause disease. These pathogenic bacteria inject several proteins and small-molecule toxins to get past host immune mechanisms.

Image related to Pear (Pyrus spp.)-Pseudomonas Blossom Blast and Dieback

Note that blossoms become increasingly necrotic when inoculated with higher concentrations of bacteria.

Photo courtesy of Bob Spotts.

Image looks like fire blight but slide labeled Pseudomonas syringae.

Larry Moore collection, 1992.

Whole shoots can dieback from this disease.

OSU Extension Plant Pathology Slide Set, 1968.

Shoot dieback from this bacterial disease.

OSU Extension Plant Pathology Slide Set.

Under favorable conditions many shoots can dieback in the spring.

OSU Extension Plant Pathology Slide Set. 1968.

Flowering pear can be a host also as seen on this Pyrus betulifolia.

Joseph Postman, 2008.

Pyrus ussuriensis is another host.

Joseph Postman, 2008.

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Apple (Malus spp.) - Powdery Mildew

Pear Cultivar Susceptibility

Note the white to gray coloration of this branch with powdery mildew.

Jay W. Pscheidt, 2012.

Note the white, strap-shaped leaves on this flowering pear that develop from buds infected last year.

Photo by Jay W. Pscheidt, 2002.

Image related to Pear (Pyrus spp.)-Powdery Mildew

Young fruit with powdery mildew colony, note the skin of the fruit is becoming discolored under the colony.

David Sugar.

Note the lighter colored shoot of this Asian pear with white sporulation of the fungus.

Photo by Jay W. Pscheidt, 1993.

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Cedar, Incense - Broom Rust

Pear (Pyrus spp.) - Trellis Rust (European Pear Rust)

Bartlett pear is not as susceptible but will show symptoms on some fruit.

Jay W. Pscheidt, 2015.

Image related to Pear (Pyrus spp.)-Pacific Coast Pear Rust

Close up of orangish cup-shaped pustules (aecia) on Pyrus calleryana (Bradford pear).

Luisa Santamaria, 2012.

Pear rust can also occur on the flower petals as well as leaves and fruit.

Jay W. Pscheidt, 2012

Note the reddish, yellow lesions on these young, misshapen fruit.

Photo by Jay W. Pscheidt, 1993.

This is a scanning electron micrograph of aecia and aeciaspores (150x).

Photo by Al Soeldner, 1999.

Numerous rust pustules (uredia) can be seen on these flowering pear leaves (Pyrus calleryana).

Photo by Melodie Putnam.

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Apple (Malus spp.) - Nectria Canker (European Canker)

Note Neonectria ditissima (formerly Nectria galligena), a fungus. Pear is susceptible but only when conditions are very favorable for disease development such as west of the Cascade Range.