58 



James G. Horsfall 



Two laboratory tests to determine the effect of sulfur and of copper 

 dusts on spore germination were made on spores from alsike and hop 

 clover. The data are given in table 19. 



TABLE 19. Effect of Copper-Lime and Sulfur Dusts on Conidial Germination 

 of Cercospora Zebrina from Hop Clover and Alsike Clover 



Treatment 



Hop clover 



Number of Per cent of 

 spores germination 



Alsike clover 



Number of Per cent of 

 spores germination 



Check 



Bank's colloidal sulfur dust. . 

 200-mesh dusting sulfur. . . . 

 7.2-per-cent copper-lime dust 



382 

 313 



350 



90.2 

 33.9 



0.0 



413 

 392 

 403 

 405 



98.6 



68.9 



96.2 



2.0 



A camera-lucida drawing of a spore germinating in sulfur is shown in 

 figure 12. A drawing of a spore in 200-mesh dusting sulfur would answer 

 for germination in the checks because it was not different. 



It would appear, therefore, that copper dusts are more likely to prove 

 valuable in the field than are sulfur dusts, although Kolodust might 

 give some control because of the colloidal sulfur that it contains. 



SOOTY BLOTCH OF CLOVER 



Suscepts 



In New York all three common clovers are affected with sooty blotch. 

 It probably is most common on alsike but scarcely more so than on white 

 clover. Red clover rarely is affected, although two collections have been 

 made, and in each case the attack was severe. Many other species of 

 Trifolium have been recorded as suscepts. These are as follows: 

 T. agrarium, T. alpestre, T alpinum, T. elegans, T.filiforme, T. fragiferum, 

 T. lupinaster, T. medium, T. montanum, T. refiexum, T. rubens, and T. 

 wormskioldii. 



The disease 



The name sooty blotch most adequately characterizes the disease. Cooke 

 (1906:247) speaks of the summer condition, clover black mould, and the 

 autumn condition, clover leaf blotch. Sooty spot is the name commonly 

 applied in the summaries of the Plant Disease Reporter. 



The disease has been collected in widely separated localities in New 

 York. In the various summaries of the diseases of cereal and forage 

 crops in the United States, this disease has been reported from Minnesota 

 to North Carolina and from Vermont to Washington. Probably it occurs in 

 the United States coextensive with the range of clover. Cooke (1906 : 247) 



