Minnesota Plant Diseases. 



349 



ridia), which are caught up by the wind and carried to an apple 

 tree or thorn tree. Here infection takes place on the leaves 

 of the host, where the cluster-cups are soon again produced. 



Fruit tree culture is often seriously damaged by this apple 

 rust, and the disease may become epidemic over considerable 

 areas. 



Since cedar trees are a harbor for the fungus, these trees 

 should be carefully watched and removed if necessary. At any 



rate, branches bear- 

 ing cedar apples 

 should be prompt- 

 ly removed and 

 burned. It has also 

 been recommended 

 that diseased leaves 

 and badly infected 

 branches of the ap- 

 ple tree be burned, 

 and that the entire 

 tree be destroyed if 

 badly rusted. Spray- 

 ing has been recommended, but 'is considered by many to be 

 of doubtful value. Bordeaux is used, and the first spray is 

 given just as the leaves expand and the second a few weeks 

 later. A third is recommended in very rainy seasons. As dif- 

 ferent apple varieties vary in their power of resistance to this 

 rust, resistant varieties may be selected where damage from 

 this rust is very great. 



The two following diseases produce leaf rusts of apple very 

 similar to the above. 



Club rust of . juniper [Gymnosporangium clavariae forme 

 (Jcq.) Rees.']. Another disease, similar in its effects to those 

 of the cedar apple and birds'-nest rust of red cedar, is a rust 

 which attacks our common juniper bushes. An attacked 

 branch swells up into a club-shaped body, often of considerable 

 length. From the surfaces arise, in early spring, small, yellow- 

 ish, club-shaped or cone-shaped groups of winter spores, which 

 swell up in moist weather. Very small spores (sporidia) are 

 produced in a similar manner to the cedar apple and these 



Fig. 182. — Rust of apple leaves. Cluster-cup stage of a 

 cedar apple fungus. After Clinton. 



