A Study of Meadow-Crop Diseases in New York 41 



more disease- free leaves than the undusted plots. This difference is 

 statistically significant, but not being great, it is in harmony with the 

 field weighings. 



In 1927 the plots were cut down accidentally by a laborer before yield 

 data could be procured, but a careful examination just before this cutting 

 showed no appreciable difference between the dusted and the undusted 

 plots. 



Several attempts to test the fungicidal efficiency of various fungicides 

 in the laboratory were ineffectual because of the difficulty of obtaining 

 satisfactory spore germination. Greenhouse experimentation on control 

 likewise is unsatisfactory because: (1) the quantity of leaves available for 

 inoculation during any one experiment is limited, since each pot of clover 

 requires a bell jar in the top of which the fruiting culture is attached; 

 (2) sporulation is erratic in pure culture, making uniform inoculation 

 almost impossible; and (3) a good method of taking data is unknown. 

 Too many pots would be required for significant yield data. Leaf, leaflet, 

 or plant counts are unreliable because of nonuniformity of inoculation. 



The indications available from field work show that sulfur will prove 

 ineffective as a fung'cide, but copper-lime dust warrants further tests 

 since a congeneric pathogene of the vine, P. tracheiphila, is controlled with 

 bordeaux mixture (Faes and Staehelin, 1927). 



The work of Williams (1927) indicates that resistant varieties may offer 

 some possibilities for control. 



powdery mildew of clover 



Suscepts 



Salmon in his monograph of the Erysiphaceae of the world (1900:178- 

 181) lists 356 species of plants in 157 genera as susceptible to the pathogene 

 of powdery mildew of clover. This extensive list includes the following 

 species of Trifolium and its near relatives, Medicago and Melilotus: 

 Medicago falcata, M. lupulina, M. sativa; Melilotus alba, M. officinalis; 

 Trifolium agrarium, T. alpestre, T. arvense, T. Jiliforme, T. hybridum, 

 T. incarnatum, T. involucraium, T. longipes, T. lit pinaster, T. medium, 

 T. minus, T. monanlhum, T. montanum, T. mora nth urn, T. paucifiorum, 

 T. pratense, T. procumbens, T. repens, T. rubens. Salmon records the 

 fungus also on other legumes, among which may be mentioned 12 species 

 of Yicia, 2 of Phaseolus, and 1 of Pisum. The work of Hammarlund 

 (1925) and of others, discussed later, indicates clearly, however, that 

 little danger of cross infection exists, because of physiologic specialization, 

 each suspect species having its own race of the pathogene. 



In New York, the writer has seen the disease on alsike, zigzag, red, and 

 white clovers. No powdery mildew has been collected on Medicago or 

 Melilotus. Moreover, a survey of American writings on meadow-crop 



