Ornamental Pear: Pear trellis rust

Biology

Pear trellis rust is a fungal disease that attacks pear trees and junipers. It is commonly reported on pear leaves in western Washington. Like many rust diseases, pear trellis rust requires both hosts to complete its life cycle. Spores produced on juniper infect only pear trees and spores produced on pear only infect junipers. However, pear can occasionally be reinfected from overwintering diseased material on the tree. Symptoms on pear appear on both upper and lower leaf surfaces. Bright yellow to orange spots up to about 1″ in diameter appear on pear leaves, twigs and branches in spring and summer. Diseased fruit may become mummified. Small fungal fruiting bodies develop in the center of the lesions on the upper leaf surface. Opposite these pimple-like fruiting bodies, additional fruiting structures (up to 1/4″ high) develop on the leaf underside. These brown fruiting bodies first appear blister-like, then develop a distinctive acorn-like shape with a pointed tip. The sides of the structure are finely divided, creating a trellis-like appearance that gives the disease its name. These may appear as early as mid-June but are more commonly found in late summer. Spores produced in the trellis structure infect species of junipers in the fall. Infected junipers do not show symptoms until the following spring or later. Symptoms on juniper can be very difficult to detect and may include spindle-shaped swellings on twigs which girdle and kill plant tissues. The fungal fruiting structures which develop on juniper consist of long cylindrical, gelatinous, reddish-brown “horns” that appear during wet weather on the swollen tissues. Infected tissues on junipers may continue to produce spores for several years. For more information, see Juniper: Pear trellis rust.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• 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.
• Carefully examine plants before adding them to your landscape. Many diseases are introduced on infected planting material.
• Complete removal of one host is the only completely effective cultural control.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• There are no products labeled for homeowner use on pear trees grown for fruit production. However, myclobutanil may be used on ornamental or flowering pear.
• Homeowners should not make foliar applications to trees over 10 ft tall.
• Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Spectracide IMMUNOX Multi-Purpose Fungicide Spray Concentrate
  Active ingredient: myclobutanil [EPA registration number: 9688-123-8845]
• This list may not include all products registered for this use.

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