708 



Journal of Agricultural Research 



Vol. XX, No. 9 



CORRELATION OF CLIMATIC CONDITIONS WITH THE DEVELOPMENT OF THE 



DISEASE IN I 91 5-1 6 



Plots of white onion sets were grown in 191 5 and 191 6 on land which 

 had previously produced many successive crops of onions and where 

 the smudge organism was known to be present in the soil. Soil tem- 

 perature records were taken at a depth of 1 to 2 inches during part of 

 the 191 5 season and most of the 191 6 growing season. The daily mean 

 soil temperatures and rainfall for these seasons are represented in figure 



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•367 // AS 19 23 27 



fit/tr 



6 /o /«»* ia zs 26 



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10 & /& 22 26 30 1 5 9 

 JULY AUGUST 



FlG. 10.— Chart from data collected at Racine, Wis., during 1915 and 1916, showing the daily mean soil 

 temperature at a depth of 1 to 2 inches, and the rainfall. The horizontal broken line represents the 

 optimum temperature for infection and development of the disease as indicated by controlled 

 experiments, the broken vertical line the date of first observation of the disease in 191s, and the heavy 

 vertical line the first appearance of the disease in 1916. 



10. The rainfall records included here are compiled from data taken 

 at the Racine (Wis.) post office, approximately 3 miles from the onion 

 set plots. The progress of the disease between the time of its first sea- 

 sonal appearance and harvest is described for these two seasons, since 

 they represent distinctly different conditions which had varying effects 

 upon the progress of the disease. 



IN 1915 



On June 28 a very few dark green stromata were found, but no acer- 

 vuli or setae had developed. The soil temperature mean was now well 



