DISTRIBUTION OF RUSTS IN THE UNITED SLATES. 9 



meridian, which marks the eastern border of the semiarid hinds of tlie 

 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 tlie 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 ijiches rusts are generally of little importance. Such 

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

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

 mountain areas, including Wyoming, much of ^h)ntana, Idaho, Utah, 

 Colorado, New Mexico, southeastern Oregon, and the interior vallej^s 

 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. Tlie 

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

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

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

 of and hicluding 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 difhcidt, 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 diliiculties being rust. Almost nowhere 

 in this southeastern part of the United States are tlie small grains, 

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



DISTRIBUTION OF THE DIFFERENT RUST SPECIES. 



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

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

 spring wheat belts of the Great Plams 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 by no means 

 unknown. In Washington and Oregon it is fre(iuent and virulent. 

 In the Ulterior mountain valleys, between the Rocky ^lountains 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 epitlemic, 

 though usually of sHght importance. On the coast of California 



216 



