584 



IOWA ACADEMY OF SCIENCE 



problem from a direction the reverse of that iu the New Eng- 

 land states, where considerable attention has been given to this 

 disease. 



Notable studies of late blight have been made under labora- 

 tory conditions, the most recent being those of Melhus 3 . These 

 have contributed important information relative to the life his- 

 tory of the fungus and cleared away a number of erroneous 

 conclusions based upon its supposed similarity to other mildews 

 whose life histories were well known. Laboratory studies, how- 

 ever important, recpiire confirmation under field conditions cov- 

 ering long periods of time and different sections of the country. 



FIELD OBSERVATIONS IN IOWA. 



In the following pages the writer has endeavored to supply 

 these field data for Iowa conditions. It is particularly inter- 

 esting to note the close parallelism between the actual condi- 

 tions of the field and the findings of the laboratory, a fact which 

 emphasizes the value of laboratory investigations for the correct 

 interpretation of field data. 



MOISTURE SUPPLY. 



One of the vital factors affecting the growth of diseases is 

 moisture supply. "When present in excessive quantities, the 

 plant growth is apt to be very succulent and sappy thus afford- 

 ing ideal feeding grounds for the parasite and these conditions 

 also augment spore production. 



The rainfall by months for the years of 1885, 1903.. and 1915, 

 is presented in the following table : 



Rainfall for Iowa. 



It will be noted that the rainfall was deficient for June in 

 two of these years. July and August were very wet for 1885, 



-Melhus, I. E., Jour. Agrl. Res. V— 2, Oct., 1915. 



