Gymnosporangium juniperi-virginianae (cedar apple rust on red cedar)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Pucciniomycotina
Class	Pucciniomycetes
Order	Pucciniales
Suborder	Uredinineae
Family	Pucciniaceae
Genus	Gymnosporangium

Scientific Name

Gymnosporangium juniperi-virginianae

Scientific Name Synonyms

Gymnosporangium macropus

Common Name

cedar-apple rust

Author: Clarissa Balbalian, Mississippi State University

Reviewed by: Alan R. Biggs, PhD., West Virginia University

Pathogen

Gymnosporangium juniperi-virginianae Schwein. is a heteroecious, demicyclic rust fungus. Telia are golden brown, 10-22 mm long and 1-2 mm wide and appear as hornlike projections from round galls on the juniper host. The telia consist primarily of 2-celled, cylindric-fusoid teliospores that are 45-65 μm long and 15-21 μm wide. Teliospores are thick-walled (0.5-1 μm thick), yellow to golden in color and have 2 pores near the septum.

Symptoms and Signs

Globose to kidney-shaped galls begin as small green leaf swellings on the branches of the juniper host and enlarge to about 10-30 mm in diameter by fall. The surface of young galls is pitted and orange tendrils of teliospores (telial horns) will develop from those pits as the gall matures. The spore tendrils are gelatinous under wet or humid conditions, and dry and shriveled during dry conditions. Twig dieback may occur distal to the galled portion of the twig.

Ecology and Spread

Gymnosporangium juniperi-virginianae is an obligate parasite of plants in the Cupressaceae (primarily Juniperus sp.) and pomaceous members of the Rosaceae. Apple and crabapple (Malus sp.) are the most commonly infected rosaceous hosts, but the fungus has also been reported on pear (Pyrus sp.) and hawthorn (Crataegus sp.). The life cycle of the fungus takes 2 years to complete. Juniper leaves are infected in midsummer to early fall by windborne aeciospores released from infections on the rosaceous host. In the spring of the year following infection, hypertrophy of the infected leaf tissue occurs and the resulting round galls become visible on the branches of the juniper host. The following spring, telia form in the juniper galls and teliospores are extruded from the telial horns during spring rains and may be airborne up to several kilometers. Teliospores remain viable for up to a day after release and germinate in situ, with basidiospores being forcibly discharged within 4-6 hours after wetting. The basidiospores infect leaves and fruits on the rosaceous host. Juniper galls are annual, they only produce telia for one season and then the gall dies and eventually falls from the plant.

Geographic Distribution

The fungus is native to North America and is not reported to occur anywhere else in the world. In Canada the fungus has been reported from Ontario and Quebec. In the United States the fungus is common in states east of the Rocky Mountains and also is reported from California and Washington.

Management

Management of any pathogen is often dependent upon both cultural and chemical options. Consult your local extension specialist or agent for recommendations relevant to your particular host and state.

Cultural Management

Galls can be pruned and destroyed before the telial horns develop. Rust resistant junipers are available for the landscape.

Juniper species and cultivars that have been reported as resistant to cedar-apple rust

Juniper species	Cultivar
Juniperus ashei
Juniperus chinensis	'Ames', 'Blue Point', 'Foemina', 'Fortunei', 'Hetzii', 'Hetzii Columnaris', 'Iowa', 'Japonica', 'Keteleeri', 'Leeana', 'Maney', 'Mas', 'Mountbatten', 'Perfecta', 'Plumosa Aurea', 'Pyrimidalis', 'Robusta Green', and 'Spartan'
Juniperus chinensis var. procumbens
Juniperus chinensis var. sargentii	'Variegata', 'Wateri', and 'Wintergreen'
Juniperus communis	Aurea', 'Aureospica', 'Cracovia', 'Depressa', 'Hibernica', 'Oblonga Pendula', 'Saxatilist', 'Suecica', and 'Suecica Nana'
Juniperus communis f. oblonga
Juniperus conferta
Juniperus horizontalis	'Admerabilis', 'Adpressa', 'Argenteus', 'Douglasii', 'Eximius', 'Filicina', 'Glomerata', 'Livida', 'Petraea', and 'Plumosa'
Juniperus xpfitzeriana	'Compacta' and 'Glauca'
Juniperus rigida
Juniperus sabina	'Broadmoor', 'Fastigiata', and 'Knap Hill'
Juniperus sabina var. tamariscifolia
Juniperus scopulorum	'Medora' and 'Moonglow'
Juniperus squamata	'Albo-variegata', 'Meyeri', and 'Wilsonii'
Juniperus squamata var. fargesii
Juniperus virginiana	'Aurea', 'Berg's Rust Resistant', 'Blue Mountain', 'Burkii', 'Globosa', 'Grey Owl', 'Hillspire', 'Kosteri', 'Pseudocupressus', 'Pyramidalis', 'Skyrocket', 'Tripartita', and 'Venusta'

Chemical Management

Junipers can be protected by making fungicide applications during late summer (July and August), when aeciospores are being released. The following active ingredients are labeled for use on juniper: azoxystrobin, mancozeb, myclobutanil, propiconazole, thiophanate-methyl plus mancozeb, triadimefon, and trifloxystrobin.

Remember: the label is the law.

Diagnostic procedures

Identification is based on the morphological characters of the gall on the plant material and the size and shape of the teliospores. Molecular diagnostic methods have not been developed, however some sequence data are available for Gymnosporangium juniperi-virginianae.

Resources and References

• Aime, M.C. 2006. Toward resolving family-level relationships in rust fungi (Uredinales). Mycoscience. 47:112-122.
• CABI and EPPO. Gymnosporangium juniperi-virginianae. Data Sheets on Quarantine Pests. Prepared for the EU under contract 90/399003. [1]
• European and Mediterranean Plant Protection Organization. 2006. Gymnosporangium spp. (non-European). EPPO Bulletin Vol. 36: 441-446.
• Sinclair, W.A. and Lyon, H.H. 2005. Diseases of Trees and Shrubs. Cornell University Press, Ithaca, NY and London.

Acknowledgments

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)