350 DISEASES OF ECONOMIC PLANTS 



More common and more injurious than the black stem 

 rust of wheat, it constitutes the destructive oat rust, totally- 

 destroying thousands of acres of oats almost yearly. As 

 with the wheat black stem rust, its attacks are epidemic, 

 fluctuating greatly in abundance and destructiveness from 

 year to year. It is usually more common in the northern 

 states than in the South. 



Crown rust {Puccinia rahmni (Pers.) Wett.). — This 

 rust is found only upon the various species of oats, and 

 in the teleutospore stage clearly differs, even to the naked 

 eye, from the other oat rust mentioned above, though 

 in the uredospore stage such separation is extremely 

 difficult without microscopic examination. 



It occurs upon oats in practically all fields and is more 

 common than its more destructive relative, the black stem 

 rust. Like the wheat orange leaf rust the damage done is 

 not serious, or very rarely so. 



The cluster-cup stage of this rust is known to grow upon 

 the common buckthorn {Rhamnus cathartica) and the 

 lance-leaved buckthorn {Rhamnus lanceolatus) . The stage 

 most conspicuous is the uredo, which forms numerous 

 orange sori upon the leaves. Later the black teleutosori 

 appear under the epidermis as long streaks which, unlike 

 most rusts, do not rupture the epidermis. 



Marked varietal resistance is shown. In Cahfornia 

 black oats are reputed to be less subject to rust than white 

 oats. In the North, the White Russian is said to be resist- 

 ant, while in the South, the Texas Rust Proof resists attack. 



Scab. See wheat. 



Phyllostictose (Phyllosticta sp.). — Browned or reddened 

 leaves with the black pycnidia profuse upon the affected 



