404 



FUNGOUS DISKASKS OF PLANTS 



Long Island, and parts of New England. In succeeding years 

 it became more serious in those sections, and spread also rapidly 

 southward and westward. It has, however, varied .greatly in 

 destructiveness in the eastern states from year to year, but on 

 the whole the asparagus industry suffered such a check that a 

 much more complete study has been made of methods of culture, 

 of direct means of control, and of varietal resistance. As a result, 

 in the East the asparagus interests have been gradually adapted to 

 the new conditions, and it is not likely that the former epidemics 

 have left any very serious impression upon this product as grown 

 for immediate marketing. 



In 1901 the rust seems to have been of the first serious conse- 

 quence in southern California, spreading northward, and doing the 

 greatest damage up to about 1905, since which time the energetic 

 control measures suggested by Smith have been effective with the 

 best growers in many localities. 



Climatological relations. It has been demonstrated that the 

 prevalence of asparagus rust in most localities bears a very definite 

 relation to climatological and other conditions. When the air re- 

 mains dry throughout the summer, rust is very largely prevented. 

 Occasional rains with intervening periods of low humidity do not 

 constitute favorable conditions for the fungus. A heavy formation 

 of dew is almost inevitably requisite to the abundance and spread 

 of the disease. This latter is of much practical importance in Cali- 

 fornia, and referring to the conditions in that state, Smith says, 

 The amount of rust varies directly and exactly with the amount of 

 dew, and so long as there is little or no dew, there can be no rust" 



Again, on light soil which has a tendency to dry out during 

 the growing season, rust is prevailingly worse than on land 

 where the plant secures the amount of moisture needed by the 

 roots. The greater susceptibility on' such lands has been attributed 

 to tin- reduced vigor of the host plant, but here also a dew relation 

 may often be a possible factor. Nevertheless, good cultivation is 

 favorable to the host plant, as innumerable experiments have 

 demonstrated. It should further be noted that the asparagus 

 under half shade is commonly free from rust. 



Host plants. Among the varieties of asparagus commonly grown 

 in the United States, the Palmetto has proved most resistant, this 



