160 MANUAL OF TREE DISEASES 



any prolonged wet period until the spores are all disseminated. 

 For further details concerning the leaf-cast diseases of conifers, 



see page 38. 



Reference 



Spaulding, P. Notes upon tree diseases in the eastern states. My- 

 cologia 4 : 148-151. 1912. 



Rust Witches'-Broom 



Caused by Melampsorella elatina (Alb. and Schw.) Arthur 



This rust disease causes witches'-brooms on various species 

 of fir (Abies) throughout their range in the United States. It 

 also occurs commonly in Canada, Mexico and Europe. The 

 young affected twigs are dwarfed and develop numerous up- 

 right laterals forming a broom-like growth. If the twigs are 

 infected at a place where no buds are present, only gall-like 

 enlargements of the bark are formed. The fungus grows out 

 into the branches and leaves of the broom. The leaves re- 

 main small and yellowish. There develop in midsummer 

 from the under surface of these dwarfed leaves two rows of white 

 blisters. The leaves then fall, leaving the broom bare during 

 the winter. New growth of the twigs and new infected leaves 

 are formed the following season. In this manner the broom 

 develops for several years and produces a crop of spores each 

 season. 



The spores (aeciospores) from the fir needles infect species 

 of Alsine and Cerastium. On these plants very small orange- 

 red or yellowish pustules are formed in late summer. Ure- 

 diniospores are produced in these pustules which may infect 

 other plants of the same species. Teliospores are formed later 

 in whitish or pale reddish spots on the under surface of the leaf. 

 They germinate the following spring producing basidiospores 

 which may infect the fir twigs. The mycelium is perennial in 

 both sorts of hosts. 



