58 Levi Otto Gratz 



control 



Although the subject of the control of wire stem was not investigated 

 thoroughly, certain phases of the experiments described above are 

 important in indicating lines of attack. The disease cannot be con- 

 trolled by changes in the environmental conditions. A low temperature 

 and a dry surface soil may reduce the disease or delay it, but not suf- 

 ficiently to warrant such a procedure as a control measure. The fungus 

 must be killed before the seed or the seedlings are placed in the infected 

 soil, if freedom from the disease is to be insured. The method of eradi- 

 cation is obviously soil sterilization. This can best be done by thorough 

 steaming of the soil or by drenching it with formaldehyde. The latter 

 method was used as recommended by Johnson, with good results (John- 

 son, 1914, and Sherbakoff, 1917, a and b). Calcium hypochlorite, up to 

 sufficient quantities to kill the host plant, had no value in controlling the 

 disease when used as a soil disinfectant. The Cheshunt mixture (Bewley, 

 1921-22) was tried at the recommended strength on several occasions. 

 At every trial there was a delay of several days in the appearance of the 

 disease, but later no difference was observed in the percentage of diseased 

 plants growing in 'treated and in untreated soil. 



SUMMARY 



Wire stem of cabbage is caused by a strain of Corticium vagum B. & C. 

 which is physiologically distinct from the strains causing lesions on potato 

 stems. Of the strains from potatoes with which the writer worked, none 

 were found to be pathogenic to cabbage, and likewise the strain from 

 cabbage seedlings did not produce lesions on potato stems. 



The minimum and maximum temperatures for the growth of the fungus 

 in pure culture are approximately 9° and 31° C. The optimum is not 

 sharply defined, but it lies between 22° and 26° C. 



The fungus exhibits a wide pH range for growth, the minimum being 

 approximately 2.0 and the maximum above 10.4. The optimum is 

 about 6.2. 



Practically any combination of soil temperatures and moistures favorable 

 for the growth of the host is favorable for the growth of the fungus and 

 for the development of wire stem. Consequently, no changes in the 

 environmental conditions will control the disease. 



