584 INSECTS AFFECTING VEGETATION 



infection of oat kernels and is capable of destroying young seedlings 

 after the manner described for wheat. (See Diseases Transmitted in 

 the Seed and also Wheat.) Like that disease in wheat, it must be 

 controlled, if at all, by a combination of seed treatment for adhering 

 spores and thorough seed recleaning to exclude all light kernels. 

 (Ohio E. S. B. 214.) 



Loose Smut of Oats. The loose smut of oats is a disease that 

 is more or less common, some years more than others, wherever that 

 crop is grown unless measures have been taken to prevent its oc- 

 currence. The disease is caused by a fungus growing within the 

 tissues of the oat plant. This fungus eventually transforms prac- 

 tically the entire head to a black dusty powder. Such smutted heads 

 are to be found, usually very readily as the oats are heading out, 

 borne on stalks somewhat shorter than normal as a rule, because 

 of the diseased condition, and consequently easily overlooked. Later, 

 at harvest time, practically all of this powdery dust has blown away 

 and scarcely anything but the skeleton of the head remains. This 

 is very inconspicuous and easily overlooked. Because of these two 

 reasons, oat smut is frequently underestimated. 



The black powdery dust of the smutted head is composed of 

 innumerable, minute bodies, nearly or quite globular, the spores of 

 the smut fungus. These smut spores mature thus in the smutted 

 heads and, being light, are blown about by the wind like dust just 

 at the time when the healthy oats are in bloom. In this way the 

 spores easily get on to the young sound kernels that are to become the 

 seed for next year's crop. Many smut spores cling to the oat kernels 

 often safely protected within the chaff. When the oats are sown 

 in the spring, the same conditions that favor their germination and 

 growth favor the germination and growth of the smut spores. These 

 latter soon push out minute germination tubes which grow into the 

 tissues of any very young oat plant within reach. Here the smut 

 fungus grows in the form of irregularly branched tubes and ab- 

 sorbs nourishment from its host; nourishment that the oat plant 

 itself should use in producing growth and seed. The smut fungus 

 keeps pace with its host through the season often branching to all 

 the stalks of a stool. The slightly dwarfed condition of the host, 

 which usually occurs, is the only effect of the smut to be seen until 

 the diseased plants head out. Then, instead of a sound head, one 

 appears with kernels and chaff wholly or in part changed to a black 

 dusty powder, masses of spores of the fungus. These spores are 

 now ready to be blown about to find lodgment on sound young oat 

 kernels where they may remain ready to infect the crop the fol- 

 lowing year after being sown with the seed in the spring. In this 

 way, then, the oat smut fungus lives over from year to year and 

 spreads. 



Since it is by way of the seed that the disease is carried over 

 from season to season, it is at once apparent that any practicable 

 method of seed treatment that will kill the smut spores without in- 

 juring the vitality of the seed is the point of attack. Several methods 

 are known that meet these requirements and the application of some 



