DANGEROUS INTERNATIONAL FOREST TREE DISEASES 95 



Eastern Gall Rust 



J. E. NlGHSWANDER 



Forest Entomology and Pathology Branch, Canada Department of 

 Forestry, Calgary, Alberta 



Cronartium quercuum (Berk.) Miyabe ex Shirai is a heteroecious 

 rust, the aecial stage of which induces perennial globose galls on stems 

 and branches of two- and three-needle pines in eastern North America. 

 Initial symptoms on pines are a slight hemispherical swelling on one 

 side of the stem usually in the region of the previous season's growth. 

 This swelling enlarges, becomes spherical, and often reaches twice the 

 diameter of the normal stem by the second year. Advance is more 

 rapid in the tangential direction than in the longitudinal. In a few 

 years the gall may completely girdle the stem, but frequently it persists 

 for many years, continuing to enlarge without girdling, and causing a 

 reduction in tree vigor. The soft wood of the gall is liable to insect 

 and rodent attack which results in entry courts for decay fungi and 

 susceptibility to wind breakage. 



Droplets of the sticky viscous pycnial fluid borne in lenticular cavi- 

 ties in the gall epidermis may appear the first, but more commonly 

 the second or third spring after infection. Pycniospores are hyaline, 

 oblong to elliptic, approximately 2 X 4/x. Aecia, with thick cerebroid 

 peridia, appear a year later on the same gall. Aeciospores are yellow 

 orange, obovoid or ellipsoid, wall coarsely verricose with one flat side, 

 15-18 X 24-29/x. 



The uredinial and telial stages occur annually on the undersurface 

 of leaves of oak and chestnut. Urediospores are yellow, ovoid to ellip- 

 soid, wall echinulate, 11-15 X 18-24/*. Chestnut-brown telial columns 

 appear in the same or new sori after the uredia. Basidiospores are 

 hyaline, ellipsoid, approximately 4 X 6/*. Where the ranges overlap, 

 this rust is difficult to distinguish from several other pine-oak rusts 

 on the oak leaves. 



In some regions this is a serious disease of pine in nurseries and 

 young plantations, although the incidence of new infection fluctuates 

 from year to year. Trees are most susceptible in the seedling stage. 

 Infections on the main stem usually result in mortality or severe 

 stunting. 



Intercontinental spread is most probable through shipments of 

 seedlings. The risk is increased by the fact that symptoms might not 

 appear for 1 to 3 years. Consequently, importations should be kept 

 under close surveillance for several years after planting. 



The taxonomy of this rust is uncertain. Some workers believed 

 it to be distinct from the Asiatic form. However, the above name, 

 based on the Asiatic Type Collection, is the only valid name in ac- 

 cordance with the International Code. In view of this confusion, im- 

 portation of susceptible hosts into Asia should be made with as much 

 caution as into other continents. 



The fungus overwinters as mycelium in the pine gall. Pycnia are 

 are produced in early spring. Aecia appear beneath the pycnial scars 

 one year later. Eupture of the peridia and wind dissemination of 



