Fir Broom Rust 



Melampsorella occurs in most of the world's fir forests. Only European foresters, 

 however, have undertaken large-scale investigation and practical control of this "most 

 important" parasite of fir (Neger 1924). In Germany Melampsorella usually infects 

 from 2 to 15 percent and occasionally 20 to 30 percent of silver fir trunks before control 

 work (Heck 1894; Flury 1932). Percentage of trees infected may be much higher, par- 

 ticularly in wet sites, if branch brooms are counted (Koch 1891; Neger 1924). Other 

 site factors and stand composition appear not to affect the amount of rust on fir in 

 Europe (Frbhlich 1931; Schwerdtfeger 1957). 



Mortality due to snow and wind breakage at rust trunk cankers is thought to be 

 important in Eurasia (Hartig 1900; Vanin 1955). But cull due to bole deformation and to 

 decay centered at rust cankers is regarded as by far the most serious form of broom 

 rust damage (Koch 1891; Schwerdtfeger 1957). Rust-caused swellings and resin accumu- 

 lations make infected trunks undesirable for pulpwood. Cankers provide infection courts 

 for decay fungi, chiefly Fomes hartigii and Pholiota adiposa (Frohlich 1931; Gaumann 

 1950; Hartig 1900). In Siberia a large part of fir heart rot is associated with broom 

 rust (Kravtsev 1933). Effects of rust brooms on tree growth rate are not thought to be 

 important in Eurasia, and Guinier (1922) claims that even the branch on which a broom 

 is located continues normal diameter growth. 



Because fir stands in Europe are managed intensively, it has proved possible to 

 eliminate rust cankers economically during regular thinnings (Heck 1927). Controversy 

 regarding the pruning of branch brooms has continued for decades, but even the "broom- 

 control" group believes that pruning prevents trunk infection and subsequent cull, not 

 that brooms themselves cause loss (Guinier 1922; Schwerdtfeger 1957). 



Fir broom rust is widespread in North America. Pomerleau (1956) reported a 

 large outbreak in the East in balsam fir, but most concentrations of the rust are in the 

 West. It is locally common in California on red fir, and was found on 3 percent of 917 

 trees of this species examined in statewide randomized plots (California Forest Pest 

 Control Action Council 1963). Serious outbreaks on white fir occur near Albuquerque, 

 New Mexico. 2 But the rust reaches its greatest known abundance on subalpine fir in 

 the Sawtooth, Cache, Caribou, and Bridger National Forests of southern Idaho, northern 

 Utah, and western Wyoming (Mielke 1957). Informal tree counts by Forest Service in- 

 vestigators on Idaho's Cassia Plateau indicated that 70 percent, 80 to 90 percent, and 

 90 to 95 percent of the subalpine fir were infected in three different localities. 



Fir broom rust in North America reduces growth and eventually causes death, 

 particularly in seedlings and saplings (Mielke 1957). Freeman (1905) and Faull (1932) 

 also reported stunting of trees by this rust. However, Boyce (1961) stated that lightly 

 infected firs seem to grow as rapidly as sound ones, and Meinecke (1916) thought that 

 branch brooms in no way affect trunks. Alexander (1958) recognized the importance of 

 trunk cankers in subalpine fir. But it appears that the ratio of trunk infections to branch 

 infections of Melampsorella is lower in America than in Europe (Boyce 1961). 



Rocky Mountain Forest and Range Experiment Station, unpublished observations. 



2 



