INTRODUCTION 



Cromrtium comandrae Pk. is a heteroecious fun- 

 gus that lives as an obligate parasite in hard pines and 

 comandras. Although distributed across North Amer- 

 ica, C. comandrae is probably most common now in 

 the Rocky Mountain States. There it produces 

 uredinia and teha on Comandra umbellata (L.) Nutt. 

 ssp. pallida {A. DC.) Piehl (fig. 1) and aecia on lodge- 

 pole pine {Pinus contorta Dougl.) and ponderosa pine 

 (Pirns ponderosa Laws.). On pine it produces the de- 

 structive canker disease (fig. 2) known as comandra 

 blister rust (Hedgcock and Long 1915 and Mielke 

 1961). This rust was believed to be an important 

 problem in the West only on ponderosa pine until 

 Mielke (1957) reported that it was also causing wide- 

 spread damage to lodgepole pine in the Rocky Moun- 

 tains. Concern developed that the rust was intensi- 

 fying and could become a serious obstacle to the or- 

 derly management of lodgepole pine. Subsequent 

 studies of the chronology of comandra blister rust 

 outbreaks in the Rocky Mountain States, made by 

 dating cankers by ring analysis, indicated that infec- 

 tion of lodgepole pine was abundant for several dec- 

 ades prior to about 1945, and since then extremely 

 scarce (Peterson 1962 and Krebill 1965). Thus the 

 comandra bhster rust damage that is now apparent in 

 lodgepole pine in the Rocky Mountain States arises 

 from old outbreaks of infection and will not increase 

 unless future outbreaks occur. To better evaluate the 

 potential threat of this rust, we must have a thorough 

 understanding of the causes of outbreaks. 



It has long been suspected that fluctuations in the 

 abundance of comandra might influence the occur- 

 rence of comandra rust outbreaks in pine. Meinecke 

 (1928) indicated that such changes were major fac- 

 tors regulating outbreaks in ponderosa pine. Some 

 evidence was provided by a severe outbreak of 

 comandra rust in the Shasta River drainage of north- 

 ern California. When the site was examined in 1914 

 by J. S. Boyce, heavily infected comandra occurred 

 commonly among recently infected ponderosa pine 

 (Wagener 1960).^ In the same area nearly 50 years 

 later Wagener (1960)^ found that the rust was still 

 common, but both comandra and young cankers in 

 pine were scarce. 



In the Rocky Mountain States fluctuations in 

 comandra populations are poorly documented. 



Mielke (1957) suggested that changes in comandra 

 abundance might be occurring in the Intermountain 

 area, and Lay cock and Krebill (1967) present some 

 evidence of change in long-term study plots. Also, the 

 fact that it is now difficult to find comandra near 

 some areas where old pine infections are abundant 

 (Peterson 1962 and Krebill 1965) indicates reduction 

 of comandra, unless the infections were due originally 

 to long-distance spread of the rust. 



The causes of changes in abundance of comandra 

 are even less well known than the influence of such 

 changes. Wagener (I960)' suggested that closing of 

 an overstory might have reduced comandra in the 

 Shasta River drainage outbreak area. This idea has 

 merit since comandra does not survive in deep shade. 

 Meinecke (1928) suggested that continual infection 

 of comandra over a number of years following a 

 buildup of comandra rust in pine causes comandra 

 populations to decUne and remain at low levels until 

 the rust dies down in pine; then comandra can rees- 

 tabhsh itself and set up conditions for new waves of 

 pine infection. This sequence of events might occur 

 on sites where comandra is not a stable member of a 

 community. However, comandra is commonly abun- 

 dant now near most old outbreak areas in the Rocky 

 Mountain States, despite frequent heavy infection of 

 the plants. The suggestion has also been made that 

 comandra has increased in the West because of over- 

 grazing (Kimmey 1958 and Mielke 1957 and 1961), 

 but a more recent evaluation casts doubts on this idea 

 (Laycock and Krebill 1967). 



Although presence of the alternate host is a 

 requirement for spread of the rust, climatic condi- 

 tions suitable for infection and development also play 

 a large part (Wagener I960,' Mielke 1961, Krebill 

 1965, and Powell 1965). The present study improves 

 our understanding of this phase of the epidemiology 

 of comandra bhster rust in lodgepole pine by reveal- 

 ing the influence of some physical factors of the 

 environment on the life cycle of C. comandrae and by 

 relating these findings to the phenology of the hosts 

 and parasite in a portion of the Rocky Mountains. 



^Wagener, W. W. Sporadic diseases in young stands 

 in California and Nevada. Pp. 14-22. IN: Proc. of the Eighth 

 Western Int. Forest Dis. Work Conf, Nov. 29-Dec. 2, I960. 

 Unpublished; permission to cite granted by W. W. Wagener. 



