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The P&PDL Picture of the Week
for 28 July 2003



Cedar-quince rust (Gymnosporangium clavipes) kills hawthorn fruit and twigs

Gail Ruhl, Interim P&PDL Director, Senior Diagnostician, Dept. of Botany and Plant Pathology, Purdue University

Have you noticed pink protrusions on the fruit of your hawthorn or dieback of branches. Check your trees closely. You may find your tree to be infected with Cedar-Quince Rust.

Cedar-quince rust affects quince (Chaenomeles), serviceberry (Amelanchier), hawthorn (Crataegus), mountain ash (Sorbus) as well as many other plants in the rose family and can cause a great amount of damage to the fruits, twigs and thorns of susceptible plants. The rust fungus requires two different tree species to complete its lifecycle. On the primary host, juniper or red cedar, the fungus infects leaves and soft shoots, becomes perennial in the living bark and causes swellings that girdle twigs and small branches. During damp weather in April and May, orange spore masses emerge from infected, swollen juniper twigs and may be splashed or blown to hawthorn, one of the alternate hosts. On the hawthorn, this fungus causes distortion of fruit, twigs, and buds. Fruits become shrunken and often die; twigs become enlarged and woody. Pinkish-orange tubes, about the size of a pencil lead, protrude from affected fruits and twigs and shed orange spores that are splashed or blown back to the juniper, completing the life cycle of this rust fungus.

Effective control of this fungal disease includes both cultural and chemical approaches.

Planting resistant varieties when installing new trees will reduce the need to invest time and money into chemical control. The following Hawthorns have shown some degree of resistance to rust.

* Crataegus crus-galli (Cockspur Thorn)
* C. intricara
* C. laevigata (Autumn Glory)
* C. phaenopyrum (Washington Thorn)
* C. pruinosa
* C. viridis (Winter King)

If rust is a chronic problem causing poor tree vigor, registered fungicides may be used on the hawthorn. These fungicides are preventive and must be applied several times during early spring to maintain a protective coating on developing twigs and fruit. Fungicides such as chlorothalonil, mancozeb or triadimefon, when used regularly during infection periods, will help control hawthorn rust. When spring weather is dry fungicide applications are generally not required. Read and follow label instructions regarding amounts of fungicide, method of application, and safety precautions.

For more information, please see the following publications (pdf):
Cedar Apple and Related Rusts on Apples in the Home Landscape
Cedar Apple and Related Rusts on Landscape Plants

Click on the small image to view a larger image.

Image from:
http://ohioline.osu.edu/hyg-fact/3000/3055.html
Cedar-quince rust

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Last updated: 28 July 2003/amd
The Plant & Pest Diagnostic Laboratory at Purdue University