Cedar Apple Rust

The causal agent of Cedar Apple Rust is the heteroecious basidiomycete Gymnosporangium juniperi-virginianae. By definition (of heteroecious) this rust fungus require two hosts to complete its life cycle. Cedar (members of the genus Juniperus) usually have the most visible symptom of the disease in the early spring as the orange gelatinous teliohorns are produced. Basidospore produced in these teliohorns are blown to susceptible apple trees where they germinate and infect. iIn late summer, after subsequent spore stages, aeciospores are blown back to the cedar where they infect and galls are initiated where they grow and mature the next year. In the spring following a year growth on the cedar, the galls give rise to teliohorns and the cycle is complete. It take two years to complete the disease cycle.

The most common host of Gymnosporangium juniperi-virginianae. in Nebraska is eastern red cedar (Juniperus virginiana). Other susceptible alternate hosts include; Rocky mountain juniper (Juniperus scopulorum), creeping juniper (Juniperus horizontalis) and common juniper (Juniperus communis).

Similar rust/host diseases American hawthorn rust and cedar-quince rust occur on American Hawthorn (Hawthorn/Gymnosporangium globosum) and Quince (Quince/Gymnosporangium clavipes),respectively. Gymnosporangium clavipes has many alternate hosts including; mountain ach, chikeberry, cotoneaster, medlar, pear, photinis, quince, flowering quince, and service berry. The galls formed by Gymnosporangium clavipes are perennial increasing in size for year to year and may remain active for 20 years.

Development of Disease

Apple host

• basidiospores germinate on leaves, and haploid mycelium spreads
• spermagonia form on upper leaf surface
• sexual reproduction begins and aecial cups form below the spermagonia on the under side of the leaf
• aeciospores are produced and dispersed

  Cedar (Juniperus virginiae) host

• aeciospores are borne on wind (up to several miles) and infect needles and axillary buds
• in the following spring, and summer, galls begin to form
• the fungus overwinters in these galls
• the following spring, wet weather will cause the galls to swell and telial horns will protrude (see picture above)
• teliospores will then germinate, produce basidiospores which will disperse, and infect the Apple host

Symptoms

Apple

• yellow to orange leaf spots and occasionally fruit spots
• spermagonia on upper surface and aecial cups on lower surface of leaves
• premature defoliation

Cedar

• galls up to 2" in diameter with surface depressions then laterprotruding horns. The telial horns are gelatinous in nature and light orange to salmon in color. The horns appear rapidly in the spring following, or during, cool rains. The horns may appear to "dry-up" between moist periods, but rapidly rehydrate to their gelatinous appearance with a new rain.

Plant Health Management

Eliminate or isolate alternate hosts

As with other heteroecious diseases, eradication, or isolation of one of the hosts is effective but is very complicated and often impractical.

Use Disease Tolerant Varieties

Apply Fungicides

Fungicides are part of the culture of apples where junipers and apple are cultivated in proximity to one another. Refer to NebGuide by University of Nebraska for current recommendations.

References

Agrios, G. N. (1988) Plant Pathology Academic Press, Inc. Calif.

Maloy, O. C. (1993) Plant Disease Control Wiley, New York

Oku, H. (1994) Plant Pathogenesis and Disease control pp. 116-7 CRC Press, Boca Raton, FL

Useful Links

University of Nebraska

Iowa State University

Ohio State University - Apple

Ohio State University - Cedar

University of Nebraska - Crab Apple Varieties

Caveat

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by:

Jane Christensen and Larry Osborne,
Department of Plant Pathology, University of Nebraska-Lincoln

Dr. John Watkins, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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