THE COISTTEOL OF CABBAGE BLACK-LEG. 



9 



may serve as sources of subterranean infection of near-by seedlings. 

 Treatments with solutions heated to 55° and 60° C. for the very 

 short periods of 1 to 5 minutes were so injurious that their effect upon 

 infected seeds was not given further consideration. It was thus very 

 evident that complete disinfection of infected seeds with a formalde- 

 hyde solution is impossible without material injury to the subsequent 

 development of the plants. Moreover, the fact that x^rotracted treat- 

 ment with this fungicide results in very serious injury to the host 

 plant precludes its use even in those special cases where complete 

 eradication of the parasite is so much desired that moderate seedling 

 injury would be tolerated. 



HOT WATEK. 



The use of hot- water treatment for the control of cabbage black- 

 leg was first suggested by Norton (8). He treated cabbage seed for 

 5 minutes at 60°, 10 minutes at 56°, 15 minutes at 56°, and 20 minutes 

 at 54° C. without injuring it, while spores of the fungus were killed 

 at somewhat lower temperatures. The effect of these treatments upon 

 the fungus within infected seeds was not determined, however. 



Table III. — Effect of hot-water treatment upon the Mack-leg fungus tvithin 

 infected cabhage seeds and upon commercial seeds. 





Length 

 of ex- 

 posure 

 (min- 

 utes). 



Effect upon 



infected seeds. 



Effect upoji commercial seeds. 





Seed 

 lot. 



Num- 

 ber of 

 seeds 

 used. 



Seeds 



with 

 viable 

 fungus 



after 

 treat- 

 ment 



(per 

 cent). 



Seeds 

 with 

 viable 

 fungus 

 and 

 ger- 

 minat- 

 ing 

 (per 

 cent). 



One-year 



-old seed. 



Two-year- 

 old seed. 



Temperature. 



Lot 2-18.1 



Lot 4-19.6 



Lot 2-18.0 





Ger- 

 mina- 

 tion 

 (per 

 cent). 



Seed- 

 ling 

 in- 

 jury, c 



Ger- 

 mina- 

 tion 

 (per 

 cent). 



Seed- 

 ling 

 in- 

 jury, c 



Ger- 

 mina- 

 tion 

 (per 

 cent). 



Seed- 

 ling 

 in- 

 jury.c 







4-18 

 1-19 

 1-19 

 1-19 

 1-19 

 1-19 

 4-18 

 1-19 

 4-18 

 1-19 



130 

 24 

 15 

 20 

 24 

 35 

 17 

 35 

 23 

 24 



75.3 

 66.6 











29.1 

 14.2 







2.8 











22.3 

 

 

 

 

 

 

 

 

 



93 







97 



O 



67 



o 



Do ... 







At 50° C 



30 



60 



5 



10 



15 

 15 

 20 

 30 

 5- 



86 

 85 

 81 

 80 

 67 

 67 



e 



91 



82 

 86 

 86 

 82 



e 

 e 



66 

 46 

 51 

 48 

 33 



e 



Do 



At55°C 



_!_ 



Do 



+ 



Do 



-t- 



Do 





At 56 to 57° C 











At 55° C 



52 

 59 



* 



39. 



+ - 



. 18 



-f 



At 60° C 























a Wisconsin Hollander variety grown at Racine, Wis., in 1918. . 



b All Seasons variety grown at La Conner, Wash., in 1919. 



c Sjrmbols used: 0= No injury; ©=slight; -f-= medium; -|-=severe. 



The effect of hot water held at 50°, 55°, and 60° C. both upon 

 commercial and infected seeds has been determined by the writer, 

 and the results of the tests are given in Table III. Treatment for 30 

 minutes at 55° C. completely eradicated the fungus, but considerable 



73603°— 22— Bull. 1029 2 



