282 MANUAL OF TREE DISEASES 



jack, lodge-pole, Jeffrey, Norway and short-leaf pines and on 

 the imported Scotch, Austrian and mugho pines. Only very 

 young trees are generally affected and it is most important as a 

 nursery and yoimg plantation disease. It is known to have 

 caused the death of a large number of the susceptible pines 

 in certain nurseries in Massachusetts, Connecticut, New York 

 and Michigan. The common weeds, sweet-fem {Comptonia 

 asplenifolia) or sweet-gale (Myrica Gale) must be in the vicinity 

 of the pines for this fungus to complete its life history. If 

 this plant is not present, the unaffected trees will not be en- 

 dangered by the diseased pines. 



Symptoms. 



This rust produces symptoms on two- and three-needle 

 pines very similar to the blister-rust which occm-s on five- 

 needle pines (see page 276). Small branches and the trunks of 

 young trees are affected. Slight enlargements are usually 

 formed. On these swollen areas yellowish blisters are pushed 

 out in early spring. The arched covering breaks and the 

 orange-colored spore-mass inside dusts out as a fine powder 

 and is blown away. 



On the sweet-fern and sweet-gale (Comptonia asplenifolia 

 and Myrica Gale), small yellowish pustules are formed on 

 the under sides of the leaves in sunmier, followed later by 

 brown bristles which project from the same spots. These 

 structures are similar to those formed on gooseberry and 

 currant leaves affected with felt-rust (see page 277). 



Cause. 



The sweet-fern rust of two- and tju-ee-needle pines is caused 

 by the fungus Cfrpnartium comptoniw ( = Peridermium comp- 

 tonice Orton and Adams), a close relative of the blister-rust fungus 

 on white pine. The life history and control of this rust-fungus 

 is similar to the white pine blister-rust except that it has 



