Damage Caused by Plant Diseases 11 



rust introduced about 1886; the white-pine bhster-rust 

 introduced from Germany shortly pi'ior to 1906; the chestnut 

 bark-disease, introduced from the Orient about 1904. Other 

 examples are cabbage club-root, potato-wart, grape an- 

 thracnose, grape black-rob, the carnation rust, and citrus 

 canker. 



Cases of interstate migration of plant diseases are numer- 

 ous, ^^^ most prominent being, perhaps, the asparagus, holly- 

 hock, carnation, and chrysanthemum rusts, and the pear- 

 blight. 



Fungi introduced into new environment, into a new con- 

 tinent, for example, owing to the change in biologic equilib- 

 rium, to the absence, perhaps, of their natural enemies or to 

 readier access to susceptible hosts are often much more de- 

 structive than in the countries from which they came. This 

 fact finds illustration in many of the diseases, mentioned 

 above, notably so in the case of the chestnut bark-disease. 



Aside from diminishing the value of the produce and the 

 thrift and future productiveness of perennials, as trees, 

 vines, etc., plant diseases entail depreciation in the value 

 of land, and in some cases even occasion large loss of life. 

 Thus the famine in Ireland in 1845 is directly traceable to 

 the injury done to the potato crop l^y the potato late-blight. 

 The presence of ergot in grain used as food for cattle or man 

 results in disease and death. 



The presence in land of the causal germ of the melon,- 

 cowpea, cotton or tobacco wilts, of onion smut, cabbage 

 club-root or black-rot, or of any one of many other soil-borne 

 pathogenes precludes the possibility of successful culture 

 of the susceptible plant for a long period of years, perhaps 

 forever, upon the soil in question. Such restriction may 

 prevent the raising of the crops that are most profitable 

 in a particular section, and in some instances depreciation 

 of 50 per cent or more in the market value of land has resulted 

 from the invasion of one of these ineradicable soil pests. 

 Still more serious is this kind of injury if the crop in ques- 

 tion is one which requires large money outlay before the 



