THE CONTROL OF CABBAGE BLACK-LEG. 25 



personal inspection by the writer of the western plantings was 

 impossible, notes were taken by a careful grower, aided by pre- 

 served specimens of the disease forwarded to him. Although the 

 plantings were kept under observation until October, he noted no 

 development of the disease, thus apparently confirming the observa- 

 tions of the previous season.^ It is possible that the dry weather 

 which usually prevails in western Washington from about June 10 

 to September 1 (5) may account for the lack of development of 

 black-leg. This matter should, therefore, be kept under observa- 

 tion for a period of years, since it is obvious that relatively minor 

 variations in amount and date of rainfall from season to season may 

 materially affect the development of the disease. In any case, this 

 experience emphasizes the necessity of greater attention than has 

 heretofore been given to the importance and practicability of secur- 

 ing cabbage seed free from black-leg infection. 



s SUMMARY. 



(1) Cabbage black-leg is a disease of increasing economic impor- 

 tance, and its appearance in epiphytotic form has been generally 

 associated with the use of infected seed. 



(2) Experimental treatments of infected and commercial seeds 

 with formaldehyde solution, mercuric-chlorid solution, hot water, 

 and dry heat have shown that the fungus can not be entirely eradi- 

 cated from infected seeds by any of these fungicides without ma- 

 terially reducing germination and causing injury to seedlings. 



(3) When infected seed is used primary lesions appear as a rule 

 on a small percentage of seedlings in the seed bed 10 days to several 

 weeks after planting. 



(4) The subsequent dissemination and development of the fungus 

 are favored by spattering water and atmospheric humidity. Con- 

 sequently, where the seed bed is located in the open, spread from 

 such primary centers to surrounding plants is dependent upon the 

 amount of rainfall and of humid weather which prevails during the 

 seedling stage. 



(5) The dissemination of the fungus in the seed bed or during 

 transplanting appears to be of much greater importance than its 

 spread in the main field. 



(6) Seed-bed trials showed that the disease was checked by seed 

 treatment, but was not completely controlled even when the treat- 

 ment was carried beyond the point where seed injury resulted. 



(7) In 1918 an epiphytotic of black-leg developed at Racine, Wis., 

 from seed treated with a 1 : 256 formaldehyde solution for 30 min- 



5 Comparative trials in Wisconsin, at Mount Vernon and Madison, were continued in 

 1921 with conflrming results. (See Walker, J. C, and Tisdale, W. B. Further notes on 

 the occurrence of cabbage black leg Abstracts of papers presented at the Toronto meet- 

 ing of the American Phytopathological Society, Dec, 1921. In Phytopathology, v. 12.) 



