Pear Trellis Rust

With the seasons slowing, there’s time to review the pests of this year, and make some mental notes for spring. Julia Turney, MG Class of 2004 and one of our Diagnostic Clinic coordinators, tells us about one annoying visitor to her garden.

Rust on upper leaf.

Rust on upper leaf.

A plant problem that didn’t come into the Diagnostic Clinic this year but did show up on my Orcas pear is Pear Trellis Rust or Pacific Coast Pear Rust. It was first noticeable as orange spots on the upper leaf surface. Later in the summer the opposite lower leaf surface grew raised bumps called aecia. The sides of the aecia are finely divided, giving a trellis-like appearance. There were 20 or so leaves on the the tree with spots and the fruit didn’t seem to be affected.

The Pacific Northwest Disease Handbook identified junipers as the alternate host for the disease. This fungus first appeared in Bellingham in 1997 and has since been found in many areas of Western Washington. Coincidentally, my neighbors new landscaping includes junipers.

The PNW handbook lists a few chemical controls but not for home use. Hortsense lists the following management options:

  • Prune out swellings or galls from junipers.
  • Remove and destroy infected material from pear trees (fallen leaves, mummified fruit, heavily infected twigs, etc.) to help minimize disease spread. To help protect junipers, infected plant material must be removed from the pear trees before spores form, usually around late August in western Washington. This may not be practical on large trees.
  • Plant only disease-resistant junipers in areas where this disease is a concern; cultivars of Juniperus squamata, J. horizontalis, and J. communis are resistant.
  • Do not plant pears and junipers within 1,000 feet of each other. Most local transmission of this disease is by wind-blown spores.
  • Aecia on lower leaf.

    Aecia on lower leaf.

    The only effective cultural control is to remove one of the hosts within 1000 feet. Logically, I don’t want to remove my pear and my neighbor doesn’t want to remove her junipers! For now, removing the affected leaves on the pear is the option available and since the tree is under ten feet tall, manageable. Hortsense has a wise suggestion for ourselves and our neighbors: Carefully examine plants before adding them to your landscape. Many diseases are introduced on infected planting material.

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