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University of Illinois Extension

Cedar Rust Differences Chart

by Jim Schuster retired University of Illinois State Extension Educator – Horticulture & Plant Pathology

 

Cedar-apple Rust

Cedar-hawthorn Rust

Cedar-quince Rust

Deciduous hosts

Apple/crabapple

Hawthorn, apple/crabapple, sometimes pear, quince, serviceberry

Many of the genera in the rose family. More common ones attacked in IL include mountain ash, hawthorn, flowering quince, and serviceberry.

Affected plant parts

Mostly leaves

Mostly leaves occasionally fruit, stems and thorns

Mostly thorns, new twigs and fruits. Sometimes petioles and veins of leaves

Leaf spot symptoms

Start as greenish yellow then yellow followed by orange (black spots[spore pustules] may form in orange), there is generally a reddish halo between infected lesion and healthy tissue

Start as yellow spot followed by orange (black spots [spore pustules] may form in orange).

Basically none except upon close inspection of veins and petioles that are swollen and occasional chlorotic spots on some rosaceae hosts.

Aecial spore release

As air dries out in a.m.

As air dries out in a.m. & during rains

As air dries out in a.m. & during rains

Evergreen hosts

Mostly Eastern red cedar in Illinois & a few other junipers not commonly grown in Illinois.

Eastern red cedar; Rocky Mountain, common and prostrate junipers as well as a few not commonly grown in Illinois.

Eastern red cedar, common, creeping, prostrate, Rocky Mountain, and savin junipers.

Gall shape

Kidney shaped to round

Flat on twig side to round

Elongated swelling of the twig

Gall appearance

Dimples/depressions by fall where telial horns develop the following spring

Raised "bubble/blister" like appearances by fall where telial horns develop the following spring.

Spindle shaped that has rough bark appearance after telia production is finished.

Telial horn appearance

Long and thin

Short and stubby

Orange bark scum

Number of years telia are produced

One year (spring following gall development)

May produce telia horns for several growing seasons/years.

Many years – sometimes for more than 20 years.

Death of twig

Twig almost always dies

Twig seldom dies

Twigs seldom die.

Distance between hosts that spores can travel to cause infection

Usually within several hundred feet but possible for several miles

Usually within several hundred feet but possible to 11 or more miles

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Filed under plants: Deciduous Trees & Shrubs

More information is available on Hort Answers.