94 James G. Horsfall 



Epiphytology 



Some epiphytological factor as yet unknown must govern the appearance 

 of timothy rust during the season, since it appears most plentifully as a 

 rule only late in the summer. During 1926, 1927, and 1928 it has occurred 

 but little before the first cutting of hay is made, but it is found frequently 

 on the growth following the first cutting. Kern (1910:417) found the 

 first timothy rust collected in Indiana in a low, wet spot on rich soil. As 

 is the case with wheat rust, the urediniospores are undoubtedly transported 

 by the wind. 



Control 



A large number of laboratory experiments with various dusts were made 

 to determine what would be likely to serve best in the field as protectants. 



Effect of sulfur. In more than ten different tests Bank's colloidal sulfur 

 undiluted always inhibited germination completely except on one slide 

 where about 8 per cent of the spores did show the initial germination. 

 The stock Kolodust always allowed a sma 1 ! amount of germination, but 

 the tubes were dwarfed and distorted considerab'y, so that infection 

 probabV would not have been produced by them had this been on plants 

 instead of glass slides. 



A typical data sheet for the three sulfiirs is given in table 25. 



TABLE 25. Effect of Sulfur Dusts on Ureoiniospohe Germination of Puccinia 



Phlei-Prate.vsis 





Total 



Treatment number of 



spores 



Per cent of 

 germination 



Check 



Bank's colloidal sulfur dust. 



Kolodust 



300-mesh dusting sulfur. . . . 



453 



97.8 



521 0.0 



483 5.6 



497 16.9 



Many other tests showed similar results for the sulfur s*. From these 

 data one would be led to conclude that diseases probably can be controlled 

 in the field with sulfur dust. 



In the spring of 1927 the effect of sulfur was tried in the field upon 

 timothy left in a two-years-old field after the clover had been killed out. 

 Eight contiguous plots, 1 by 3 rods in size, separated by alleys 1 yard wide, 

 were dusted checkerboard fashion with Kolodust, making four dusted and 

 four undusted plots in the experiment. The first application was made 

 on May 3, just as the first new green leaves were beginning to appear. 

 Subsequent applications were made on May 13, May 29, and June 19. 



4 The germ tubes produced in contact with various dusts are drawn with a camera lucida in figure 22" 

 Note that the germ tubes which develop in the sulfur dusts are gnarled and distorted, so that they probably 

 are too weak to get through the stomata. 



