96 



THE CEREALS IN AMERICA 



sown cereals, of which the wild mustard is the most common. It is so common in 

 spring wheat that the seed has become a by-product of flouring mills. The mus- 

 tards are tall prickly plants with large leaves and bright yellow flowers. The wild 

 mustard is distinguished from the black mustard on account of its long knotted pod 

 being a stout two-edged beak. Seeds are dark bro\\Ti to black, commonly spherical, 

 one-twentieth of an inch in diameter, slightly granular-roughed. It has been found 

 that by spraying wheat or oat fields wth a three per cent solution of copper sul- 

 phate (about ten pounds to the barrel, or forty gallons, of water) at the rate of fifty 

 gallons of solution to the acre, the mustard may be killed without injury to tlie 

 cereal.l The treatment is most effective if made in clear bright weather. 



145. Fungous Diseases. — The more im- 

 portant fungi which attack the wheat plant 

 are given below : 



(i) Rust {Piiccmia graminis Pers. and 

 P. rubigo-vcra (D C.) ) 



(2) Wheat scab {Fusarititn roseum Lk.) 



(3) Loose smut {Ustilago tiitici Jen- 

 sen.) 



(4) Stinking smut (Tilletia foe tens 

 B. & C.) 



Another little studied fungus causes rather 

 conspicuous dark spots upon the glumes of 

 wheat, and has been given the name of 

 ''glume spot." There is no known remedy. 



146. Rust. — The rusts of wheat in the United States 

 belong to two closely allied species, black stem rust and 

 orange leaf rust, only the latter of which it is believed 

 can pass the winter in the wheat plant.2 There are two 

 stages of rust found on the wheat plant : (i) the red rust, 

 caused by one-celled spherical uredospores, which com- 

 monly does not survive the winter, and (2) the black rust, 

 caused by elongated two-celled ieleutospores, which may 

 pass the winter upon the ripened plant. It is believed 

 that the rust plant may enter the wheat plant at the 

 time of germination, or later if opportunity offers. 



The loss caused from rust is difficult to estimate, but it is undoubtedly very large. 

 It is encouraged by hot moist weather during the ripening period. There is nc 



1 Cornell Bui. 216 (1904), p. 107. 

 % P. rubigo-vera (D C.) 



x^^ 



The black rust on wheat 



