DISTRIBUTION OF RUSTS IN THE UNITED STATES. 11 



Even as far north as Wisconsin regions are known where oat growing has 

 been discontinued on account of rust, and epidemics have been known 

 to extend to the Canadian line and even beyond. Two features of 

 an oat-rust epidemic explain instances of successful crops which often 

 occur in the midst of an epidemic. They are (1) the great variation 

 in time of ripening of different varieties of oats, amounting to as much 

 as three weeks or a month in some latitudes, and (2) the apparent 

 suddenness of the appearance of the epidemic. Frequently a variety 

 one week later than another will be ruined by rust, while the earlier 

 variety will escape entirely. This results in the presence every year 

 of considerable rust, amounting to a severe attack in some localities 

 and on some varieties, while other localities and varieties escape. 



Stem rust of barley. — The occurrence of stem rust of barley (Puccinia 

 graminis Tiordei) 1 is practically coextensive with the culture of that 

 grain, but its presence is not often a serious menace. In general, 

 the early date of maturing of barley seems to assist this crop in 

 avoiding injury. Barleys planted very late — for instance, those 

 planted for fodder — are sometimes seriously attacked, while the 

 grain barleys usually escape damage. It may be noticed, however, 

 that this rust, like the stem rust of oats, is not so nearly confined to 

 the stem as the wheat stem rust, but is often abundantly present 

 on the leaves. The rust assumes more serious proportions in the 

 Southern States. In the Great Plains area and in the dry inter- 

 mountain districts it is comparatively rare. 



Leaf rust of barley. — Leaf rust of barley (Puccinia simplex (Korn.) 

 Erikss. and Henn. ) seems to be of recent introduction. It was reported 

 from Iowa in 1896, from California in 1905, from Minnesota in 1905, 

 1906, 1907, and 1908, and occurred in Virginia in 1906 in a considerable 

 degree. In 1910 it was abundant at Laurel, Md., and also occurred 

 in Virginia. The most abundant outbreak was in Virginia, in 1906, 

 where the plants were well covered with rust. In Minnesota it 

 seems to appear late in the season and has had no injurious effect on 

 the crop. It may be classed as one of the least conspicuous of the 

 grain rusts in point of economic importance. 



Stem rust of rye. — The stem rust of rye (Puccinia graminis secalis 

 Erikss. and Henn.) is fairly common, but causes little injury. The 

 explanation of this probably lies in the fact that winter rye is grown 

 almost exclusively in the United States, and the stem rust appears 

 at so late a date as to cause no appreciable damage. It was fairly 

 common in Minnesota in 1906-1908 in experimental plats on spring 

 rye, and in 1909 was abundant. As these were light rust years as 



1 As shown later, the physiological specialization of this rust in the United States is sufficiently different 

 from that of the stem rust on wheat to make a distinction in the name desirable, and the trinomial termi- 

 nology, as here applied, is used throughout this paper. 



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