158 THE CULTIVATED EVERGREENS 



Oak rust* is caused by the fungus Cronartium cerebrum, 

 Hedgcock and Long, and affects many two- and three-needle 

 pines, especially the scrub, jack, Sabine, Monterey, and knob- 

 cone. Large gall-like swellings are produced on the branches 

 or trunk, and in some cases witches'-brooms are formed. 

 The alternate host is the oak, the leaves of which are infected 

 by the spores from the pines. 



Some two- and three-needle pines, especially the lodge- 

 pole and western yellow, are injured by Castilleja rust, which 

 is caused by the fungus Cronartium coleosporioides, Arthur. 

 On western yellow pine it has been found to cause serious 

 losses in some nurseries, where the alternate host, Castilleja 

 miniata, is an abundant weed. Extensive swellings of the 

 branches and trunk are produced, somewhat resembling the 

 previous disease in this respect. 



Sweet-fern rust is destructive in some nurseries. It occurs 

 on two- and three-needle pines, giving rise to symptoms very 

 similar to those described under the white-pine blister-rust. 

 The alternate hosts are the sweet fern {Comptonia asplenifolia) 

 and sweet-gale {Myrica Gale). 



Rust witches'-broom of spruce is caused by a Melampsorella 

 species which has its alternate stage on Alsine (sandwort), 

 Cerastium (mouse-ear chickweed), and Stellaria (chickweed). 

 The disease is wide-spread and very harmful in some localities 

 on Engelmann, Norway, black, Colorado blue, and Sitka spruce. 

 It not only attacks and stunts the twigs and branches of young 

 trees, but also brooms and dwarfs saplings and older trees. 



Rust witches'-broom of fir causes harmful brooming and 

 dwarfing of the tips of various species of fir (Abies) . Cerastium 

 and Stellaria are again the alternate hosts. 



* The existence of the fungi causing these diseases depends on the close proximity 

 of the coniferous and alternate hosts. Control measures will be as outlined under 

 "White pine blister rust." 



