586 INSECTS AFFECTING VEGETATION 



mode of attack is similar. The two are taken up together in this 

 publication chiefly because of the similarity of preventive measures. 

 The occurrence of stinking smut of wheat over the state is not so 

 general as that of either the loose smut of oats or the loose smut of 

 wheat. The stinking smut of wheat occurs only where smutty seed 

 wheat has been used or clean seed has been inoculated with such 

 smut spores in some way in handling. Where this disease does occur, 

 however, it is usually far more destructive than the loose smuts of 

 oats or wheat, sometimes destroying as much as one-half of the crop 

 or even more, and rendering the remainder almost worthless. The 

 same method as with oats can be used for estimating the percentage 

 of smut present in any field. In addition to the amount of grain 

 actually destroyed by the smut, the sound wheat that remains is 

 heavily docked on the market because of the well known fact that 

 such wheat produces flour of very poor quality. It is therefore 

 important to give special attention to keeping this smut from the 

 crop or eradicating it if it is present. This can be done. It is neces- 

 sary, however, to know something of the habits of the fungus which 

 causes the disease so as to be able to proceed intelligently to com- 

 bat it. 



Development and Spread of the Disease. The stinking smut 

 of wheat is caused by a parasitic fungus, which, like the oat smut 

 fungus, is carried over from year to year by spores attached to the 

 kernels of the seed grain and sown with them. Infection of the 

 very young wheat plants takes place in a way similar to that with 

 oats. The fungus grows up within the tissues of its host and when 

 the latter heads out the parasite enters the young kernels and trans- 

 forms the contents of each into a dark brown, dust-like, somewhat 

 greasy, ill-smelling mass, the spores of the fungus. The disagree- 

 able odor given off by this smut, from which character it gets its 

 name, is often so striking at harvest time that it is sometimes notice- 

 able to a considerable distance on the windward side of a badly 

 affected field. This odor is especially noticeable when such wheat 

 is threshed and for some time thereafter in the product. 



Thus, instead of heavy, well filled heads of sound wheat, the 

 diseased plants produce heads that are worse than worthless. Such 

 heads are very light and consequently remain usually quite erect. 

 The glumes or chaff of the affected heads are not attacked by this 

 smut. They are, however, often abnormally distended by the short, 

 puffy smutted kernels, which sometimes show between them. In 

 general appearance the smutted heads are similar to the sound ones; 

 when the smutted kernels are examined, however, a rather striking 

 difference is at once evident. The smutted kernels or smut balls 

 are of a dead, light brown color, often with an olive green tint. In 

 form they are usually shorter and thicker than the sound kernels 

 and the characteristic deep crease of the latter is no longer present. 

 This gives the smut balls their characteristic puffy appearance. The 

 smutted kernels remain whole until broken in some mechanical way 

 in handling the grain. When thus broken the spores attach them- 

 selves to anything with which they come in contact, such as the 



