196 MANUAL OF TREE DISEASES 



Leaf- and Twig-Rusts 



Caused by species of Gymnosporangium 



A few species of the rust-fungi belonging to the genus Gym- 

 nosporangium attack the green twigs and leaves of various juni- 

 pers without causing any over-growth of the affected parts. 

 The symptoms of these diseases are confined to the brown spore- 

 masses developed either on the leaf or between the leaves. The 

 life history of these forms is similar to the other species of the 

 same genus and is discussed on page 192. Below are given the 

 hosts and characteristics, in brief, of these diseases. 



In Colorado, Utah and New Mexico, the Utah juniper is at- 

 tacked by G. inconspicuum Kern. A yellowing of the leaves 

 on the affected twigs may be noticed and in early spring small 

 brown cushion-like spore-masses, the size of a pin-head, are 

 formed from between and around the margins of the appressed 

 scale-like leaves. The alternate Stage occurs on species of 

 service-berry. 



In Colorado a similar appearing species, G. midtiporum Kern, 

 attacks the Utah and one-seed juniper. The alternate hosts 

 are not known. 



In Texas several species of juniper are attacked by G. exiguum 

 Kern. Short brown conical spore-masses, a sixteenth of an inch 

 long, are pushed out from the affected leaves. The alternate 

 host is Cratwgus Tracyi. . 



In northeastern and north central United States, Juniperns 

 sibirica is attacked by G. Damsii Kern. Spore-masses appear 

 as small brown pustules on the leaves or at the base of leaves on 

 the twig. The alternate stage occiu-s on species of mountain ash. 



A foreign species, G. koreaense (P. Henn.) Jackson, recently 

 has been found established in Oregon on an imported juniper, 

 Juniperus chinensis. Spore-masses form on the leaves of the 

 juniper. The alternate stage occurs on cultivated quince and 

 introduced Asiatic species of quince and pear. 



