Preface. 



IT is probably safe to say that millions of dollars are lost in Minnesota yearly 

 by the ravages of plant diseases. Agriculturists and horticulturists all over 

 the world have of late years directed a great deal of attention toward the 

 study of plant diseases and the methods of combating them. The Department of 

 Agriculture of the United States has done vastly more than any other institution in 

 the world along this line and the results have been well worth the efforts, for many 

 efficient methods of fighting these pests have been devised. 



In many cases w^here cure is impossible an intelligent understanding of the con- 

 ditions and effects of a disease '^ili aid in prevention. The dissemination of such 

 knowledge is of very great value. It is a very evident fact that all agricultural pur- 

 suits are taking great strides, and the education of those boys and girls who are about 

 to cultivate or manage the cultivation of lands is becoming more and more impera- 

 tive. 



The possession of an accurate knowledge of plant diseases and their causes is not 

 only of commercial use to the farmer, both in cure and prevention, but also, by 

 making him an intelligent observer, adds hosts of assistants to the small corps of men 

 who are devoting their time to this study of botanical science. The advantages of 

 such a condition amongst agriculturists would far surpass those where the mere 

 knowledge of present methods of prevention and cure obtains. In fact it is only w^ith 

 the intelligent and hearty co operation of farmers that such work can successfully go 

 forward. 



It b not the aim of tliis work therefore to catalogue all of the ills that Minnesota 

 plants are heir to, but its cliief object is to disseminate knowledge of the destructive 

 parasites of the useful plants of this state, to assist all concerned in the cultivation of 

 plants to a more intelligent and thorough understanding of the habits of these para- 

 sites, and to point out established methods of combating such diseases. Recipes are 

 not the aim of such a work — these are of value and as such are introduced; but by 

 far the most valuable effort should be the inculcation of the knowledge of the habits 

 and life-stories of those organisms which are the causes of disease. Upon such 

 knowledge, widely disseminated, can be built a substantial system of disease preven- 

 tion. In short, the aim of this work is rather educa.Uona.1 than immediately practi- 

 caU for in the former feature the author hopes that it will be ultimately most useful. 



