26 



James G. Horsfall 



It is seen from the table that on the basis of the percentage of leaves 

 infected, a control of 8 per cent was obtained in experiment no. 1, but the 

 difference is probably not even out of the range of experimental error. 

 The difference due to treatment is much less in experiment no. 2 than in 

 experiment no. 1 and is not significant. 



It is evident from table 10 that the experiments in the greenhouse 

 confirm the laboratory tests, showing that Macrosporium sarcinaeforme is 

 tolerant of sulfur. 



A single test was made in the greenhouse to see if copper-lime dust is 

 as effective in preventing infection as it had been shown to be in inhibiting 

 spore germination. Standard copper-lime dust was applied before in- 

 oculation to the leaves that had been moistened previously with tap water. 

 The results of the counts, which were made after eight days had elapsed, 

 appear in table 11. 



TABLE 11. Effect of Copper-Lime Dust on Infection by Macrosporium Sarcinae- 

 forme in the Greenhouse 



Difference = 3. 52 ±0.42 

 D 



E,i 



8.38 



Obviously the copper did prevent some infection, because the leaves in 

 the dusted lot averaged only about 50 per cent as much infection as the 

 undusted leaves. The laboratory tests, however, indicated that better 

 control should have been obtained. A single greenhouse experiment is 

 insufficient to warrant the conclusion that copper-lime dust would prove 

 ineffective under field conditions, especially in view of the results obtained 

 in the laboratory. 



When all the tests are considered, it appears that sulfur dusts or sprays 

 cannot be relied upon to give control of this disease but that copper-lime 

 dusts are promising. 



