Pacific Northwest 1998 An Online Guide to Plant Disease Control

FactSheets offer superior print quality for the page you are currently viewing. Using Microsoft's Internet Explorer has given best printing results.
Glossary
Guide Home
Search

OSU Extension Office
 
Pear -- Pacific Coast Pear Rust
See Also: Cedar, Incense -- Broom Rust ; and Pear -- Trellis Rust
 
Cause: Gymnosporangium libocedri, a fungus. Similar spore stages are produced on hawthorn, Amelanchier, apple, crabapple, mountain ash, and quince. The alternate host is the incense cedar (Calocedrus decurrens). The disease has been reported often from the Willamette Valley of Oregon, but outbreaks are economically significant to growers only every few years. (Note that G. asiaticum is on Asian pears.)
Symptoms: Pear fruit are malformed while young and drop from the tree. Bright yellowish to orangish spots with numerous cup-shape pustules (aecia) develop over the fruit surface. Spots fade and darken as the fruit matures or falls off the tree. Green shoots and leaves also are attacked but not as frequently. Oriental and European cultivars are susceptible. ‘Winter Nelis’ is severely affected, but ‘Bartlett’ is not. Symptoms are most obvious after flowering but before July.

The disease on Incense cedar is called broom rust because it causes a witches’ broom. Telia develop only on the leaves and are not very noticeable until during spring rains when they look like orange jelly. Trees with many infections decline and may die.

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

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

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

 
Cultural control: Remove alternate hosts around the orchard.
Chemical control: The following do not specifically list this pear rust but can be used to control the disease. Apply during the time cedar trees have swollen, orange tellia in early spring. In western Oregon this is usually during bloom.
  1. Flint 50 WG at 2 to 2.5 oz/A. Rotate with other fungicides that have different modes of action. Do not apply more than twice consecutively, exceed four applications total per season, use more than 11 oz/A/season, or use within 14 days of harvest. 'Concord' grapes may be injured if accidentally sprayed. 12-hr reentry.
  2. Procure 480 SC at 8 to 16 fl oz/A. Do not apply within 14 days of harvest or more than 64 oz/A per year. 12-hr reentry.

Chemical control only for flowering pear

  1. Contrast 70 WSP at 3 to 6 oz/100 gal water. 12-hr reentry.
  2. Eagle 20 EW at 6 to 12 fl oz/100 gal water. 24-hr reentry.
  3. Heritage at 1 to 4 oz/100 gal water plus a non-silicone based wetter sticker. 4-hr reentry.
  4. ProStar 70 WP at 3 to 6 oz/100 gal water. 12-hr reentry.
  5. Spectracide Immunox at 1 fl oz/gal water.
References:
Wilson, E.E. and J.M. Ogawa. 1979. Fungal, Bacterial, and Certain Nonparasitic Diseases of Fruit and Nut Crops in California. Berkeley, CA: University of California, Division of Agricultural Sciences, Agricultural Sciences Publications.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
Top

In print since 1954 and on the web since 1996. Questions or comments, please contact us.