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IPM Scouting in Woody Landscape Plants

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Cedar–apple rust, Gymnosporangium juniperi-virginianae, Cedar-hawthorn-rust, G. globosum, Cedar-quince rust, G. clavipes
IPM scouting in woody landscape plants > cedar–apple rust, cedar-hawthorn-rust, cedar-quince rust
Hosts: These fungi require two different hosts to complete their development: an evergreen host (mainly junipers) and a rosaceous host. Cedar-apple rust, Michigan trees, shrubs
How it’s spread: These rusts overwinter on their evergreen hosts and produce jelly-like masses of orange telia from perennial galls during warm, wet weather in spring. Telia give rise to a different type of airborne spore that infects members of the rose family.

Management: Galls on junipers can be pruned off and destroyed before spore horns develop, but usually, only rosaceous hosts need protective fungicides. Apply labeled fungicides to broadleaf hosts as orange telial horns are first visible on juniper and repeat at several week intervals. Select resistant cultivars where possible when making new or replacement plantings.
Cedar apple rust galls on twig Small galls of cedar-quince rust on twig
Symptoms on junipers: Gelatinous telia on junipers: (left) Cedar apple rust galls on twig; (right) Small galls of cedar-quince rust on twig.
Fruit damage Leaf damage Tree damage
None of these rusts kill their hosts, but cedar quince rust is the most disfiguring, producing not only leaf spots, but deformed fruits and petioles and stem galls. Cedar apple and cedar hawthorn rusts produce similar rusty orange leafspot symptoms and premature leaf drop. ‘Cluster cups’ form on backs of leaves and form spores that are carried on the wind and infect only junipers.

Additional information

This information was developed from A Pocket IPM Scouting Guide for Woody Landscape Plants by Diane Brown-Rytlewski. Purchase this in a pocket-sized guide for reference in the orchard from MSU Extension (publication E-2839).
The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the Michigan Agricultural Experiment Station, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.
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Updated 7/17/07