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Need to know:
- Yellow spots that eventually enlarge on hawthorn leaves.
- Fruits will have an orange rusty tubes with dust like substances (signs).
- The disease occurs during rainy spring weather, and spores are spread to nearby hawthorns by the wind.
- Removing as much of the infected twigs while leaving the fruit and leaves intact is a good method of sanitation.
- Some fungicide treatments can be used to prevent symptoms.
Hawthorn rust is caused by the fungus Gymnosporangium globosum.
Symptoms of cedar-hawthorn rust
The rust fungus causes small yellow spots on hawthorn leaves. These spots eventually enlarge and often have a reddish border. The centers of these yellow spots later show small black spots. On the lower leaf surface, small brownish tube-shaped structures form directly above the spots. Infected leaves may eventually yellow and drop prematurely from the tree.
Signs of cedar-hawthorn rust
On Fruits, tubes with orange spores mases (rusty dust like substance).
Disease cycle of cedar-hawthorn rust
This disease is also called cedar-hawthorn rust because the fungus requires two hosts to complete its life cycle.
The cedar-hawthorn rust fungus overwinters on junipers or red cedars in round, brown galls on leaves and twigs. During rainy spring weather, these galls produce bright orange, gelatinous tendrils that contain fungal spores. These spores are then blown to nearby hawthorn trees. Spores may be blown several miles. Fungal spores produced in infected hawthorn leaves in late summer are then blown back to the juniper host, completing the life cycle.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa, please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us.
Want to submit a sample? Follow the foliar instructions on Submitting Trees and Shrubs page.
Plant Resistant hawthorn varieties when available.
Sanitation: remove as much of the infected twigs, fruit and leaves as possible.
Some fungicide treatments available can provide protection prior to the symptoms have appeared. Fungicides can be used to protect hawthorn leaves from infection. Labeled products include chlorothalonil and EBDC products. Fungicides should be applied as new growth appears and flower buds start to open. Repeat 3 or 4 times as directed by the product label. Control on the juniper host is usually not necessary.
See this article for more information about cedar rusts.
Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.
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