DANGEROUS INTERN ATIOXAL FOREST TREE DISEASES 91 



Spruce Broom Rust 

 R. S. Peterson 



Forest Service, U.S. Department of Agriculture, Fort Collins, Colo. 



Chrysomyxa arctostaphyli Diet. (Peridermium coloradense A. & 

 K.) is a perennial witches'-broom of spruce in North America. First 

 symptom is probably needle etiolation. Release of dormant buds re- 

 sults in formation of brooms, which bear annual crops of yellow-green 

 needles. Abundant pycnia produced on these needles in late spring 

 give off a strong, foul odor detectable for 50 meters or more. Aecio- 

 spores produced during summer give entire brooms a yellow-orange 

 appearance. Fungus mycelium invades bark and outer xylem of 

 branches and trunks, often giving rise to secondary brooms and oc- 

 casionally causing formation of cankers and fusiform swellings. 



Aeciospores infect Arctostaphylos uva-ursi (L.) Spreng., a common 

 associate of spruce in Eurasia. Basidiospores produced on this trail- 

 ing, woody plant are believed to infect spruce in early summer. There 

 are no urediniospores. It has been suggested, but not confirmed, that 

 spruce-to-spruce transmission by aeciospores also occurs. 



Spruce broom rust is similar to the broom rust of Abies (Melamp- 

 sorella caryophyllacearwm, (DC.) Schroet.). They may be distin- 

 guished not only by host but also by the looser, larger brooms on 

 spruce and by microscopic characteristics of the fungi. Distinct woody 

 swellings are more commonly caused by the fir parasite, which also 

 changes the shape and color of infected needles more than does the 

 spruce rust. 



Spike-tops, dead branches, and mortality, are commonly associated 

 with spruce brooms. Presence of dead brooms near trunks is usually 

 an indicator of heart rot. 



Seldom are more than 25 percent of the spruces in a stand infected : 

 in most stands fewer than 1 percent bear brooms. 



Intercontinental spread is possible on infected plants and perhaps 

 by windblown aeciospores, which survive several months' storage. 

 However, the telial host is a very unlikely target because of its thick 

 cuticle and lack of stomata on upper leaf surfaces. 



Range : Nearly coextensive with the range of spruce in Xorth America, 



but more common in the West. 

 Hosts : 

 Pinaceae — 



Piceadbies (L.) Karst. where planted 



P. engelmannii Parry 



P.glauca (Muench) Voss 



P. mariana (Mill.) BSP 



P. pungens (Engelm.) 



P. rubens Sarg. 



P. sitchensis (Bong.) Carr. 

 Ericaceae — 



Arctostaphylos uva-ursi (L.) Spreng. 

 Literature : 

 Bourchier. R. J. Alberta and Rockv Mountain Parks forest disease 



survey. Forest Ins. and Dis. Surv., Div. For. Biol., Sci. Serv., 



Canad. Dept. Agr., Ann. Rpt. 1952: 121-126. 1953. 



687-137 0—63 7 



