THE CONTROL. OF CABBAGE BLACK-LEG. 3 



It was upon the basis of these facts that the present investigation 

 was begun. It was necessary, first of all, to determine more definitely 

 the limitations of seed treatment with the common disinfectants, 

 both upon commercial cabbage seed and upon the black-leg fungus 

 within infected seeds. Following this, the relation of certain en- 

 vironmental factors to the development and spread of the disease, 

 especially in the seed bed, and their influence upon the ultimate 

 success of seed treatment were studied. This paper is a progress re- 

 port upon the work along these lines. 



EFFECT OF FUNGICIDAL TREATMENT IN THE LABORATORY 

 UPON SEED AND THE SEED-BORNE FUNGUS. 



Because of its practical bearing upon the efficacy of seed treatment, 

 an extensive study was made of the resistance of the fungus within 

 infected seeds to heat, desiccation, and chemical fungicides, and, as 

 a necessary corollary, experiments on the effect of the same treat- 

 ments upon normal cabbage seeds were performed. Early experi- 

 ments showed that it would be impossible completely to disinfect 

 seed without producing some detrimental effect upon its vitality. 

 From the standpoint of practical cabbage culture, however, seed 

 treatment can be carried somewhat beyond the point of first injury 

 with profit if sufficient benefit is to be derived from fungicidal action. 

 Moreover, as will be pointed out later, where it is desirable to rid 

 small quantities of " mother seed " of the black-leg fungus before 

 introducing the seed into a new locality, quite severe treatment may 

 be desirable with the aim of complete eradication of the parasitic 

 organism. For these reasons, in the laboratory experiments treat- 

 ment with disinfectants was usually prolonged to the point where 

 complete eradication was attained, and the effect upon commercial 

 seeds up to that point was determined. 



Four types of treatment were used: (1) Mercuric chlorid, (2) for- 

 maldehyde, (3) hot water, and (4) desiccation at moderate and high 

 temperatures. For the study of the effect of treatment upon the 

 fungus, seeds directly beneath or very close to pod lesions were col- 

 lected shortly before maturity. Two such lots were used, one (No. 

 4-18) secured in a field of the Wisconsin Hollander variety at Racine, 

 Wis., in July and August, 1918, and the second (No. 1-19) collected 

 by Mr. E. E. Clayton from a field (variety not determined) at Matti- 

 tuck. Long Island, N. Y., in July, 1919. The earlier and more ex- 

 tensive experiments were performed with the former lot, and the 

 stronger treatments were repeated or performed for the first time 

 with the latter. 



The seeds were exposed to the various treatments and placed on 

 potato-agar plates. They were kept at room temperature for two 

 to four weeks, within which time the fungus, if viable, was identi- 

 fied by its growth on the medium. 



