152 THE FORAGE AND FIBER CROPS IN AMERICA 



the complaint that land does not grow clover as readily as 

 formerly is not uncommon, the necessity for a lapse of years 

 between crops has not been clearly recognized. The causes 

 for this condition are not understood. The causes which may 

 be ascribed for the failure of clover are as follows: (i) fungous 

 diseases; (2) insect enemies; (3) lack or exhaustion of one or 

 more essential elements, particularly potash; (4) unfavorable 

 physical properties of the soil and sub-soil, particularly the 

 latter; (5) acidity of the soil; (6) lack of the tubercle-forming 

 and nitrogen-gathering bacteria. It is probable that the causes 

 mentioned have been operative at different times and places in 

 preventing the growth of clover. 



162. Fungous Diseases. Gursow studied the "clover-sick" 

 plants at Rothamsted in 1901 and identified a fungus (Peziza 

 ciboroides Fries, Sclerotinia ciboroides Rehm.) which was suf- 

 ficient to destroy the plant in the manner in which most of the 

 clover was affected throughout the clover-sick region. This 

 fungus has long been known to do considerable damage in 

 northern Germany. Alfalfa, white clover, and other leguminous 

 species are affected by it. Gursow states that in the earlier 

 stages of the disease, when the dark spots first occur on the 

 leaf, spraying with Bordeaux mixture would modify if not 

 check the disease. 1 



In Tennessee, where the failure of red clover to grow has 

 become pronounced, an anthracrtose (Colletotrichum trifolii 

 Bain) has been found attacking both red clover and alfalfa, 

 but to which alsike clover appears to be immune. It is believed 

 to be the most serious plant disease occurring in that state. 

 While the plant may succumb to the disease at any time, the 

 most critical periods appear to be when the seedlings encounter 

 the first prolonged spells of summer and again when the plant 

 ripens its seed. 2 



ijour. Roy. Agr. Soc. Eng. No. 64 (1903), pp. 376-91. 

 2 Journal of Mycology, 12 (Sept., 1906), pp. 192-3. 



