DISTRIBUTION OF RUSTS IN THE UNITED STATES. 9 



meridian, which marks the eastern border of the semiarid lands of the 

 central United States. It thus includes a large portion of the great 

 grain-growing districts of this country. The rusts are also very severe 

 and of annual occurrence in the small, isolated districts on the west 

 side of the Coast Range in California, in eastern and southern Texas, 

 and in parts of the Atlantic Coast States. They are an important 

 factor in the grain-growing regions of eastern Washington and Ore- 

 gon. In general, where the annual rainfall is 20 inches or more, rust 

 may be a serious menace to crops. In areas where the annual rainfall 

 is less than 20 inches rusts are generally of little importance. Such 

 dry areas occur in the United States just east of the Rocky Mountains, 

 extending eastward to the ninety-eighth meridian and in the inter- 

 mountain areas, including Wyoming, much of Montana, Idaho, Utah, 

 Colorado, New Mexico, southeastern Oregon, and the interior valleys 

 of California. Here in most years rusts are comparatively rare, 

 though in the great rust epidemic of 1904 some of these areas, includ- 

 ing California, were affected. 



AREAS MOST LIABLE TO RUST. 



The area where rust is particularly a menace is the hard spring- 

 wheat belt of Minnesota, North Dakota, and South Dakota. The 

 States bordering the Ohio River Valley, including Kentucky, Illinois, 

 Indiana, and Ohio likewise are frequently attacked by rust. In the 

 Southern States of the eastern half of the United States — that is, south 

 of and including Tennessee and North Carolina — rust of certain cereals 

 has been so serious as almost to prohibit the growing of them in those 

 regions. It is very difficult, for instance, to grow spring oats profit- 

 ably in portions of the southernmost tier of States east of the Missis- 

 sippi River, one of the chief difficulties being rust. Almost nowhere 

 in this southeastern part of the United States are the small grams, 

 with the exception of winter oats, grown at all extensively. 



DISTRIBUTION OF THE DIFFERENT RUST SPECIES. 



Stem rust of wheat. — The stem rust of wheat (Puccinia graminis tritici 

 Erikss. and Henn.) is of great importance in the hard winter and hard 

 spring wheat belts of the Great Plains area and in the States bordering 

 the Ohio River. In Maryland, Virginia, and other Eastern States it 

 has been almost entirely absent for many years, but is b}^ no means 

 unknown. In Washington and Oregon it is frequent and virulent. 

 In the interior mountain valleys, between the Rocky Mountains and 

 the Sierra Nevada Mountains, and in the nonirrigated western area of 

 the Great Plains, it is only occasionally found and is seldom serious. 

 In the interior valleys of California it is occasionally epidemic, 

 though usually of slight importance. On the coast of California 



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