I02 Minnesota Plant Diseases. 



The success of smut infection depends largely upon the abil- 

 ity of the spores to germinate and the germination of the spores 

 at a suitable season for attacking the host-plant, e. g., in oats, 

 in the seedling stage. An epidemic of smut must, therefore, be 

 preceded by a season favorable to spore germination and also 

 coinciding with the seedling stage of the grain. Such epidemics, 

 moreover, are greatly favored by the clinging of smut spores to 

 the grains since they are thus sure to be near the latter when 

 these commence to grow. 



Many other causes of epidemics might be mentioned. Un- 

 der so-called normal conditions the fungus may create no ex- 

 traordinary damage but under propitious conditions it becomes 

 epidemic. One can easily understand that any disease may be- 

 come epidemic if the conditions are right, and since the horti- 

 cultural and agricultural changes instituted by man are so great 

 in many cases it is to be expected that the danger of epidemic 

 diseases is always an important and ever-present source of 

 trouble. The older horticulturists and agriculturists took cog- 

 nizance of epidemics only after they occurred, when, of course, 

 remedial measures were impossible. Now the raiser of plants, 

 just as does the medical practitioner among men, keeps close 

 watch upon all kinds of diseases and attempts to prevent epidem- 

 ics rather than to cure them. Every introduction of a plant into 

 a new country and new surroundings, every appearance of a new 

 hybrid opens up new fields for numerous parasites who may find 

 in the newcomer just the right conditions for an epidemical 

 growth. Every introduction of a new plant to a certain com- 

 munity may also bring new fungus diseases which may be able 

 to attack plants of this community if the latter have not learned 

 to withstand their attacks. Thus may -result an epidemic simi- 

 lar to that of mallow rust. It is useless to suppose that 

 we shall ever get rid of the plant disease question and be able 

 to lay it aside under the weight of a few rules for spraying or 

 other treatment. On the contrary, the more complex and ad- 

 vanced our agriculture and horticulture become even more so 

 becomes the question of immunity from fungus epidemics. As 

 the host plants vary so also may the fungi, and those parasites 

 which are apparently harmless today may in years to come be 

 very dangerous pests. 



