THE CONTROL OF CABBAGE BLACK-LEG. 



21 



Table VIII. — Development of cabhage dlaclc-leg in commercial fields planted with 

 treated seeds in the Baoine, Wis., district in 1918. 





Treatment. 



Field 



No. 



Diseased plants. 





Seed lot. 



Infected. 



Pre- 

 vented 

 from 

 heading. 



Date of 

 obser- 

 vation. 



No. 2-17 





2 

 3 



1 

 1 

 4 

 5 



Per cent. 



87 

 99 

 99 

 74 

 37 

 83 



Per cent. 

 87 

 96 

 91 

 14 

 52 

 65 



Nov. 2 



No. 3-17 a 



do "...' 



Do. 



No. 3-17 a 



do 



Nov. 5 



No. 4-17 a 



do 



Do. 



No. 5-17 



do 



Oct. 30 



No. 5-17 



do 



Nov. 1 





five fields 





Average, 



79.8 



67.5 











a Treated by seed grower. 



RESULTS IN 1919. 



The observations were continued at Racine in 1919 and were ex- 

 tended to the Appleton and Shiocton districts in east-central Wis- 

 consin, where certain quantities of the No. 2-18 and No. 3-18 lots of 

 seed had been distributed. Most of the seed in all of these sections 

 was sown about May 9. Because of the poor showing made with the 

 formaldehyde solution in 1918, treatment with a 1:500 solution of 

 mercuric chlorid for 30 minutes was recommended for general use 

 in the spring of 1919. A small quantity of untreated No. 2-18 seed 

 was sown in the Racine district on May 9. As already noted in 

 the experiments conducted at Madison, the disease developed first 

 and most rapidly from the untreated seed. When the beds at Ra- 

 cine were examined on June 12, black-leg had become widespread in 

 the plant ig of untreated No. 2-18 seed. From the treated seed, how- 

 ever, very little of the fungus had developed at this date. Most of 

 the transplanting was done within the next two weeks, and the 

 disease was effectively checked in most fields, as shown by the re- 

 sults of a survey at the end of the season (Table IX). This was un- 

 doubtedly due to the fact that the development of primary infec- 

 tions was retarded and the number reduced by mercuric-chlorid 

 treatment coupled with the fact that only two rainy periods occurred 

 during the remainder of the month — one on June 13-16 and the 

 other on June 24. (See fig. 1.) * 



In one bed under observation, where practically no black-leg was 

 noted on June 11, the disease had become widespread by July 1. 

 Two plantings were made from this bed, the first (field 1, Table IX) 

 about June 12 and the second (field 2, Table IX) about July 2. A 

 comparison of the two fields at the end of the season, as given in 

 Table IX and illustrated in Plate II, brings out the effect of extensive 

 spread of the disease in the seed bed previous to transplanting. In 



