Cedar Hawthorn Rust: An In-Depth Exploration of a Complex Plant Disease

Cedar Hawthorn Rust, caused by the fungus Gymnosporangium globosum, is a fascinating disease that affects both cedar (juniper) trees and hawthorn trees. This disease is part of a group of rust diseases involving junipers and various rosaceous hosts, creating a complex lifecycle that requires two different types of plants to complete. In this comprehensive blog post, we will explore the details of Cedar Hawthorn Rust, its symptoms, lifecycle, and the strategies available to manage and control this disease.


Cedar Hawthorn Rust is primarily found in North America, where both cedar and hawthorn trees are common. The disease can lead to aesthetic issues and weaken the affected plants, making them more susceptible to other diseases and environmental stresses.

Symptoms and Identification

Cedar Hawthorn Rust manifests differently on cedar and hawthorn trees:

On Cedar Trees:

  • Galls: Round, woody galls form on twigs and branches.
  • Orange Gelatinous Horns: During wet spring weather, orange gelatinous horns emerge from the galls, releasing spores.

On Hawthorn Trees:

  • Leaf Spots: Bright yellow-orange spots appear on the upper leaf surface.
  • Fruit and Twig Infections: The disease may also infect hawthorn fruit and young twigs, causing deformities.

Lifecycle and Transmission

The lifecycle of Gymnosporangium globosum is complex and involves two hosts:

  1. Infection of Cedar: The fungus infects cedar trees, forming galls that take a year or more to develop.
  2. Spore Release from Cedar: In the spring, gelatinous horns emerge from the galls, releasing spores that infect hawthorn trees.
  3. Infection of Hawthorn: The spores infect hawthorn leaves, causing leaf spots and sometimes fruit and twig infections.
  4. Spore Release from Hawthorn: In late summer, spores are produced on the hawthorn and spread to cedars, starting the cycle again.

Management and Control

Controlling Cedar Hawthorn Rust requires an integrated approach:

1. Cultural Practices

a. Plant Selection

Planting resistant varieties of both cedar and hawthorn can prevent the disease.

b. Pruning

Removing galls from cedar trees and infected leaves from hawthorn trees can reduce disease pressure.

c. Proper Spacing

Planting trees with adequate spacing can improve air circulation, reducing humidity and infection chances.

2. Chemical Control

a. Fungicides

Sprays with fungicides can be used on hawthorn trees as preventive measures during the infection period.

3. Environmental Control

a. Water Management

Avoiding overhead watering can reduce leaf wetness, limiting the chances of infection on hawthorn trees.


Cedar Hawthorn Rust is a complex and intriguing disease that highlights the intricate relationships between different plant species and pathogens. While typically not a devastating disease, it can cause significant aesthetic issues and weaken the affected plants.

By understanding the biology of Gymnosporangium globosum and implementing a combination of cultural, chemical, and environmental strategies, it is possible to manage Cedar Hawthorn Rust effectively.

The story of Cedar Hawthorn Rust serves as a vivid example of the complexity of nature and the interdependence of different species. Whether you’re a commercial grower, a home gardener, or simply interested in the wonders of plant pathology, the exploration of this disease offers valuable insights into the delicate balance that defines the world of plants. It’s a reminder of the ongoing challenges and triumphs of understanding and managing the diverse and beautiful organisms that share our environment.