Cedar-apple rust

  • Cedar–apple rust, Gymnosporangium juniperi-virginianae
  • Cedar-hawthorn-rust, G. globosum
  • Cedar-quince rust, G. clavipes

Hosts

These fungi require two different hosts to complete their development: an evergreen host (mainly junipers) and a rosaceous host.

Rosaceous hosts of rusts

Cedar apple

Cedar hawthorn

Cedar quince

  • Apple
  • Crabapple
  • Apple
  • Crabapple
  • Hawthorn
  • Quince
  • Mountain ash
  • Amelanchier
  • Apple
  • Crabapple
  • Hawthorn
  • Quince
  • Mountain ash
  • Amelanchier
  • Cotoneaster

Symptoms on junipers

Ceder apple rust Quince rust
Gelatinous telia on junipers: (left) Cedar apple rust galls on twig; (right) Small galls of cedar-quince rust on twig.

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.

Symptoms on rosaceous hosts

Quince rust Cedar apple rust Cedar apple rust
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

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.

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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 AgBioResearch, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.