52 



Journal of Agricultural Research 



Vol. VI, No. I 



ing this time and the few days just preceding, the humidity remained 

 above 60 for a longer time on an average and the minimum humidity 

 did not become so excessively low nor the temperature so excessively 

 high as during the time previous to July 4. 



The next period of pronounced increase in conidial production was 

 from July 19 to 23 (fig. 6, curves D, E, G), when the conditions were more 

 favorable than during any period of similar length through the summer, 

 the humidity ranging above 60 on an average of 19.4 hours each day and 

 not falling below 52 (fig. 7), and the temperature ranging from 60° to 

 90° F. 



Conidial production was again above the average (curves M, N, and O) 

 from August 9 to 13, during which period the humidity remained above 

 60 from 13 to 20 hours each day and there was a small amount of rain 

 which seemed to aid in maintaining the necessary humid conditions. 

 Production was checked on August 16, on which date the temperature 

 was 102° and the average humidity low, and was again inhibited after 



Fig. 8.— Curves of the comparative production of conidia on the upper and lower surfaces of the leaf spots, 

 representing series E. K, N, and G of Table V and figure 6. Rocky Ford, Colo.. 1913. 



September ii, subsequent to which date the minimum temperatures 

 ranged from about 30° to 45° and the maximum from about 65° to 83°, 

 while the humidity remained above 60 for 12.4 hours per day, on an 

 average. 



The general conclusion from these tests is that conidial production is 

 greatly influenced by temperature and relative humidity, or speaking 

 specifically — 



(i) A temperature of 100° F. or over is detrimental to conidial pro- 

 duction, directly perhaps because it is inimical to the growth of the 

 fungus and indirectly because humidity is ordinarily excessively low at 

 such an extreme temperature. 



(2) Conidial production is greatly checked at daily temperatures 

 ranging below 50° as a minimum and 80° as a maximum. 



(3) The most favorable temperature for conidial production is 80° to 

 90° in the daytime and not below 60° at night. 



(4) The temperature being favorable, the largest conidial production 

 occurred at the higher humidities. A good production occurred when 



