5.10 THE SMALL GRAINS 



555. Control measures for rust diseases. No means 

 has yet been devised for the eradication of cereal rusts, 

 and there are no effective remedies. The investigations 

 of Galloway, Wiitrich, and the author (Hitchcock and 

 Carleton, 1894) have shown that certain fungicides will 

 kill the spores in all cases where the rust has broken 

 through the epidermis. It appears impossible, however, 

 with any appliances yet available, to reach all affected 

 portions of the plant with a fungicide spray, on a practi- 

 cal scale in large fields. Many sori occur on the under 

 sides of the leaves, and often the leaves turn over. Driv- 

 ing through the fields, at the time the rust is worst, will 

 also destroy much grain. 



556. Prevention of rust. Prevention of rust is possible 

 to a considerable extent. Where wet seasons are usual, 

 the crop should not be grown on low lands. A heavy 

 stand in humid districts is favorable to rust. Under these 

 conditions, it should be noted that the atmospheric humid- 

 ity is the influencing factor, and not the moisture in the 

 soil, except as the latter may affect the immediately over- 

 lying stratum of air. In fact, a soil over-wet may be 

 inimical to the fungus if unfavorable to the host. Stakman 

 (1914, pp. 34-36) investigated this subject and concluded 

 that " the water relation in the soil which is most favor- 

 able for the host plant's development is also the most favor- 

 able for the development of the rust." 



Well-balanced fertilization of the soil is important in 

 this connection. Over-feeding with nitrogenous fer- 

 tilizers, by causing greater vegetative growth and succu- 

 lence of the host, is, in the same proportion, conducive 

 to rust. 



Earliness of the crop is a very important favorable 

 factor in enabling it sometimes to escape rust. Either 



