298 



Minnesota Plant Diseases. 



small tubes which bear secondary spores in great abundance; 

 these spores are capable of yeast-like budding when brought 

 under favorable conditions, e. g., in piles of manure ; in this 

 manner the infecting ability of the disease is greatly increased. 

 These secondary spores are conveyed by the wind or other 

 agency to other plants and infection follows. Only young 

 parts of the plants can be successfully attacked. The disease is 



only local in its effects, and in 

 this character it differs very de- 

 cidedly from such smuts as loose 

 smut of oats and stinking smut 

 of wheat. The part most fre- 

 quently attacked is the cob and 

 the harvest is often seriously 

 diminished by this disease. Cer- 

 tain varieties of sweet corn are 

 peculiarly susceptible to attack, 

 so that a selection of varieties is 

 often advisable. 



Treatment of seed corn with 

 copper sulphate or formalin has 

 absolutely no effect on this smut. 

 If the disease has been bad in 

 the preceding year, fresh manure 

 should be avoided, as the multi- 

 plication of the spores is in- 

 creased by its use. All smut tu- 

 mors and spore masses must be 

 burned as soon as discovered. 

 Bordeaux spray has been found 

 successful to a certain extent, 

 but usually is unnecessary if the 

 spore masses are carefully removed. 



Head smut of sorghum [Sphacelotheca reiliana (Kuhn.) Clin- 

 ton]. This smut attacks the whole head of the sorghum plant 

 and often all of the heads of a plant. The smut mass therefore 

 replaces the entire head and is at first surrounded by a fine 

 white membrane, which later ruptures and exposes the smut' 

 powder. Grains, glumes and all parts of the head are de- 



FiG. 148. Smut of corn (Ustilago may- 

 dis), on left, on the leaf of the corn; 

 on the right, in the tassels (stami- 

 nate inflorescence). After Clinton. 



