Hsiang, T. and J. Richter. 1999. Juniper Rust Species in an Ontario Nursery, 1998. Canadian Plant Disease Survey 79:142-143.

CROP: Juniper



T. Hsiang and J. Richter

Department of Environmental Biology, University of Guelph, Guelph, Ontario, N1G 2W1

tel: (519) 824-4120x2753, fax: (519) 837-0442, email: thsiang@uoguelph.ca



In early May, 1998, samples of juniper rust were collected from Guelph, Ontario and Georgetown, Ontario to determine the prevalent species. In mid-May, 1998, a nursery near Georgetown, Ontario was examined for the occurrence of juniper rust diseases on six different cultivars of Juniperus scopulorum. Each tree was inspected for at least five minutes to inventory all rust infections. The number of infections by each rust species, and the height and location of each tree were recorded. Ten trees per cultivar were examined.


Only cultivars of J. scopulorum were found to have rust infections. Although species and cultivars were mixed between rows in the nursery near Georgetown, no rust infections were found on any cultivar of J. chinensis. Three rust species were found on samples collected. Gymnosporangium clavipes was readily distinguishable due to the fusiform swellings on twigs and larger branches (Fig. 1). While both G. globosum (Fig. 2) and G. juniperi-virginianae ( Fig. 3) formed galls, those of G. juniperi-virginianaewere much larger. When present, telial horns could also be used to distinguish these latter two species: those of G. juniperi-virginianae were longer and more cylindrical than those of G. globosum, which were shorter and wider. These descriptions of the Gymnosporangium species agree with those found in Sinclair et al. (1989).

In addition to macromorphology, microscopic features were also used especially where identification was not certain. Teliospores of G. clavipescan be identified by the carotiform shape of the pedicel (Fig. 4). Spores of G. globosum (Fig. 5) and G. juniperi-virginianae ( Fig. 6) have cylindrical pedicels, but these species are distinguishable by the shape and size of the spore body. Spores of G. globosum are 30.0 to 53.6 m in length (Parmelee, 1965), and are ellipsoid with obtuse ends ( Fig. 5). Spores of G. juniperi-virginianaerange in length from 40 to 75 m (Parmelee, 1965; Laundon, 1977), and are also ellipsoid but with tapered ends (Fig. 6). After exposure to water, teliospores will swell and form distinctive jelly-like structures. Here is an example of teliospores of G. globosum (Fig. 7).

There were striking differences between J. scopulorum cultivars in incidence of different rust infections (Table 1). Only the cultivar Moffettii had visible infections of G. juniperi- virginianae. Among juniper species, J. scopulorum and J. virginiana are the most susceptible to this fungus, with only a few cultivars of J. chinensisand J. horizontalis susceptible (Sinclair et al. 1987). Wichita blue showed a very high level of infection by G. globosum, but all cultivars showed some level of infection. The most common juniper hosts of this fungus are J. scopulorum and J. virginiana, with J. horizontalis and J. communis to a lesser extent (Sinclair et al., 1987). .Gymnosporangium clavipes was found on all cultivars except Gray Gleam. This fungus is found on J. virginiana, J. scopulorum, J. horizontalis, J. communis and a few other species (Sinclair et al., 1987)

In an early paper on susceptibility of Juniper cultivars to two rust species in Illinois, cultivars of J. scopulorum were found to be very susceptible to G. juniperi-virginianae but resistant to G. clavipes.

A more recent report on susceptibility of juniper cultivars to G. juniperi-virginianae in Kansas found almost no infections on J. chinensis cultivars, and low to heavy infections on different cultivars of J. virginiana and J. scopulorum (Tisserat & Pair, 1997). Among the cultivars in common between that study and the current one, moderate levels of rust infection were found on Moffettii and Gray Gleam, low levels on Skyrocket and Wichita Blue, and none on Medora. This illustrates that disease ratings may differ between different locations, and hence more local testing of susceptibility should be conducted before recommending juniper cultivars for rust disease resistance.


Laundon, G. 1977. Gymnosporangium juniperi-virginianae. CMI Descriptions of Pathogenic Fungi and Bacteria No. 547. Commonwealth Mycol. Inst., Kew, England.

Parmelee, J.A. 1965. The genus Gymnosporangium in eastern Canada. Can. J. Bot. 43, 239-267.

Sinclair, W.A., H.H. Lyon and W.T. Johnson. 1989. Diseases of trees and shrubs. Comstock Publishing Assoc. Ithaca, New York. p.240-249.

Tisserat, N.A., and J.C. Pair. 1997. Susceptibility of selected juniper cultivars to cedar-apple rust, Kabatina tip blight, Cercospora needle blight and Botryosphaeria canker. J. Environ. Hort. 15:160-163.

Table 1. Incidence of Gymnosporangium rusts on Juniperus scopulorum cultivars in an Ontario nursery in late May 1998.


G. clavipes G. globosum G. juniperi-virginianae
Skyrocket 27.2 ± 0.97a 27.3 ± 1.10  0 ± 0  163 cm
Wichita blue 7.9 ± 0.36  84.1 ± 2.43  0 ± 0  169 cm
Greenspire 2.4 ± 0.53  5.3 ± 0.38  0 ± 0  139 cm
Medora 0.3 ± 0.05  9.3 ± 0.72  0 ± 0  140 cm
Gray Gleam 0 ± 0  2.6 ± 0.20  0 ± 0  108 cm
Moffettii 12.5 ± 0.74  27.4 ± 1.26  0.2 ± 0.04  158 cm
a Number of rust infections are followed by standard error calculated from 10 trees per cultivar

NOTE: another site with photos of Juniper rust