18 BULLETIlSr 1029, U. S. DEPARTMENT OF AGRICULTURE. 



been observed where alternate rows or groups of rows in the main 

 field, from two different seed beds, resulted in one lot of plants wilt- 

 ing badly from black-leg, while the other was not affected. An in- 

 stance of tliis is shown in Plate I, B. Thus, although exact experi- 

 mental data have not been obtained, these general field observations 

 indicate that, under Wisconsin conditions at least, the spread of the 

 disease in the main field is not nearly so important as that in the seed 

 bed or during transplanting, 



SEED-BED TRIALS AT MADISON, WIS., IN 1919. 



In order to supplement experiments performed in the laboratory, 

 treated samples of seed from lots.Nos. 2-18 and 3-18 were sown out 

 of doors. Each of these lots contained a small percentage of infected 

 seed. A level strip of silt-loam soil was selected, which had not 

 grown cabbage for at least seven years. Single-row plats 7 feet long 

 and 18 inches apart were used. Two-gram samples of each treat- 

 ment were planted on May 10 and 12. The various treatments in- 

 cluded with the final results obtained are given in Table VII. 



In the check plats of untreated seed which were sown on May 14 the 

 disease appeared on June 9 and was fairly well advanced by July 1, 

 the normal time for transplanting. In all the treated plats the ap- 

 pearance of the disease was materially checked. On June 20 four 

 centers of disease were found, one in each of the 12, 24, and 48 hour 

 treatments of lot No. 2-18 with dry heat at 85° C, and one in the 

 24-hour dry-heat treatment of lot No. 3-18 at the same temperature. 

 In the last case the disease had spread to 15 adjoining plants and to 

 one of the adjoining plants in the case of another center. On June 27 

 one infected plant each was found in the formaldehyde 1 : 256 30- 

 minute and the 1 : 128 1-hour plats. Thus, up to that date very 

 little disease had developed, and had the plants been set in the field 

 at this time, which would have been the normal time for transplant- 

 ing, the disease would probably have been very successfully con- 

 trolled. 



In order to give the parasite all possible opportunity to develop 

 in the plats, however, the plants were not disturbed until July 31, 

 when they were all pulled and examined for black-leg. The data 

 given in Table VII show that the disease continued to develop and 

 spread from primary centers during July. Very few plats were en- 

 tirely free from the disease, which is in general accord with the re- 

 sult of laboratory experiments. 



