The Dry Root-Rot of the Bean 1027 



much higher than that on either side. However, observation in most 

 bean fields will show that the outside rows are composed of low-yielding 

 plants. In other respects the data for this experiment are not difficult 

 to analyze. Weather conditions were such as to make the effect of the 

 dry root-rot very noticeable. The decrease in yield in diseased rows 

 averages approximately fifty per cent. 



CONTROL 

 ROTATION OF CROPS 



Since the cause of the dry root-rot is a soil pathogene, the possibility 

 of controlling the disease through longer crop rotations was considered 

 very early in these investigations. The common rotation practiced by the 

 growers of dry shell beans is but three years, and frequent instances are 

 found in which the rotation is only two years. It is customary to follow 

 beans with wheat and then clover, although in the fruit-growing districts 

 this rotation may vary somewhat. In all localities, however, a few 

 growers vaiy their rotations considerably. For this reason a survey was 

 made in Wyoming County in 1915, and in Genesee, Livingston, and Mon- 

 roe Counties in 1916, to determine whether these variations in rotation 

 affect the disease to any extent. Very little information was obtained. 

 Fields were observed in which beans had not been grown for ten years 

 and yet the dry root-rot was present. In some of these fields the patho- 

 gene might have been continuously returned to the soil in the manure. 

 On the other hand, this explanation could scarcely hold for pasture land. 



One point drawn from the survey that should be noted is, the shorter 

 the rotation the more serious is the disease, although long rotations do 

 not eradicate the fungus. From this it appears that the pathogene will 

 accumulate more rapidly in the presence of the bean plant. Neverthe- 

 less it still persists in the absence of this host plant, and, as far as is known, 

 no other crop grown in rotation with the bean and no weeds found com- 

 monly in the fields are susceptible to its attacks. It would thus appear 

 that the fungus lives saprophytically in the soil. It is not uncommon 

 for pathogenic members of the genus Fusarium to do this, since they 

 frequently have been isolated from the soil in the absence of their host 

 plant. Pratt (1918) isolated Fusarium radicola Wollenw. and F. tricho- 

 thecioides Wollenw., two potato pathogenes, from virgin soil in Idaho. 



