A Study of Meadow-Crop Diseases in New York 



45 



to inoculation, the average green weight of the dusted plants was 1.74 

 times as much as that of the undusted ones, and their dry weight was 

 1.53 times as much. These data appear in table 17 (page 52). Ap- 

 parently the mildew reduced the crop from one-third to one-fourth. The 

 two photographs in figure 8 show the difference between the two series. 



Symptomatology 



In New York the disease rarely appears prior to the first cutting. It 

 may occur as early as July 20, but in 192d, 1927, and 1928 it has not 

 developed in abundance until after August 15. The first sign of the 

 disease is a barely perceptible patch of white cobwebby growth on the 



Figure 9. a 



LEAF OF BED CLOVER IN THE EARLY STAGES OP INFECTION BY ERYSIPHE 

 POLYGON! 



upper surface of the leai (figure 9). These patches increase in size, finally 

 coalesce and give (lie leaf the superficial appearance of having been 

 sprinkled with flour. When a considerable number of leaves are diseased, 

 the whole field appears white from a distance. 



By the time the mycelium has covered the leaf, the tissue begins to 

 show necrotic effects. Dark purple to black irregular spots appear in 



