12 MASS. EXPERIMENT STATION BULLETIN 361 



of disease being present where humidity conditions were rather indifferently 

 regulated and where the minimum temperature bordered 60° F. 



The same comparisons were made in the fall cropping season of 1930. There 

 were 28.7 percent more infected leaflets in greenhouse B where a fixed minimum 

 temperature of 60° F. maintained only a limited control of the relative humidity 

 than in greenhouse A where a fluctuating automatically controlled temperature 

 and forced ventilation operated fairly well to keep the relative humidity under 

 85 percent (Table 9). 



Table 9. — Relation of Automatic Humidity Regulation and Automatic 

 Temperature Regulation to the Control of Tomato Leaf Mold 



Fall Cropping Season 1930. 



Percentage of Diseased Leaflets 

 Date of 



Foliage Counts House A House B 



Humidity Temperature 



Control Control 



October 17, 1930 19.7 21.9 



November 21, 1930 25.4 41.2 



December 26, 1930 18.2 35.7 



January 26, 1931 10.3 63.3 



Total 18.2 46.9 



The average yield in pounds per plant in each greenhouse was: 



Grade of Greenhouse Greenhouse 



Tomatoes A B 



No. 1 pounds 2.32 2.9 



No. 2 pounds 1.00 1.3 



No. 3 pounds .37 .5 



Total 3.69 4.7 



The higher yield did not coincide with better control of the disease, which 

 suggests the operation of other limiting factors. Obviously, the fuel cost of reg- 

 ulating the conditions in greenhouse A was greater than in greenhouse B. 



Further comparisons were made in the spring cropping season of 1931. The 

 disease was equally bad in both greenhouses. After May 15 all the ventilators 

 were kept open day and night; nevertheless, the disease, which had already ap- 

 peared, eventually spread to all of the foliage. The yield and quality of the toma- 

 toes did not appear to be seriously affected. Where the humidity was kept fairly 

 well below 85 percent within a temperature range of 60° to 75° F., the yields 

 averaged 10.28 pounds per plant, of which 7.35 pounds were of first grade, in 

 contrast to a total of 11.92 pounds of which 8.63 pounds were of first grade, under 

 a minimum temperature of 60° F. and natural ventilation. The yields were 

 considered exceptionally good, but relative humidity below 85 percent with tem- 

 peratures between 60° and 75° F. again showed an adverse influence on yield. 



A further comparison of the two sets of conditions was made in the fall of 

 1931. A difference of only 10.1 in percentage of infected leaflets could be shown 

 (Table 10) in favor of automatic humidity control and forced air. 



