996 - EXPERIMENTAL FARMS 



'^ 5 GEORGE v., A. 1915 



The situation in this district was made more grave by the appearance at numer- 

 ous points of a disease the cause of which had hitherto been little known or studied, 

 namely Thielavia hasicoJa or Tobacco Root Rot. 



For some time it had been observed that some land, after having been planted ta 

 White Burley for a period of years, refused longer to produce a normal crop of this 

 variety, no matter what care was taken in preparation of the soil. Moreover, this 

 state of affairs seemed to become worse from year to year. 



Certain varieties like the Seed Leafs seemed to do well on these lands, where the 

 Burley would no longer grow, and hence such soil was termed " Burley sick." The 

 phenomenon was explained as being the action of soil toxins on the roots of the plant 

 which had secreted them, but which were without effect on the roots of other varieties 

 of the same botanical group. 



In reality, whatever the effect of these toxins may be, they did not enter into this 

 question. The true cause was a larval form of Tobacco Root Rot, Thielavia Basicolfi, 

 a disease well enough known, but whose common form consisted of an almost complete 

 decomposition of the fibrous roots and even of the main root up to the level of the 

 crown. In the form observed in Ontario, however, the only trace of the disease consisted 

 of brown spots, hardly visible to the naked eye, at the ends of the fibrous roots. In 

 most cases, apart from the feeble appearance of the plants attacked, no trace of the 

 disease could be observed, the affected portion of the roots remaining in the soil 

 unless the plant was lifted with the greatest care. 



Expert opinion traces this disease to the nature of the materials employed in 

 making the seed-beds. One frequently notices, on bush land, that the disease 

 has attacked the wood violets and cyclamens, and it is soil of this very character that 

 is used, on account of its dark colour and great fertility, for the upper portion of the 

 seed-beds, wherein are placed the seeds. On germination, the roots are rapidly 

 infected, causing what is commonly known as root rot. 



However, although the study of this disease on the plantation had been incom- 

 plete, it has been carefully observed in its action on the seedling. Among some planters, 

 the seed has been subjected to treatments aimed at freeing it from the germs of 

 TJiielavia hsicola. But the process of disinfection (generally treatment of the mould 

 by steam) was applied too late, since the fields themselves had become infected. 



Plant pathologists who had interested themselves in this question claimed that 

 the use of artificial fertilizers with an acid reaction (as the superphosphates) would 

 allow of the establishment of soil conditions unfavourable to the development of the 

 germs of Thielavia hasicola. A set of experiments to test this was laid out, in colla- 

 boration with Walker & Sons, in the autumn of 1913. Unfortunately, certain repro- 

 ductive forms of Thielavia are very resistant and can remain in the dormant state 

 for five years, until favourable conditions for development again appear. One can 

 easily understand that, under these conditions, the struggle would be a severe one, and 

 its success, owing to possible oversight, far from assured. 



At any rate, the importance of treating the mould by steam or formalin has been 

 brought to the attention of the tobacco-planters of Ontario and suitable methods have 

 been indicated. 



The efficacy of the steam treatment has been placed beyond question; it remains 

 to show the value of the use of formalin for this purpose, it being more convenient 

 for most growers to Tise. 



The formalin treatment has been used for four years at the Central Experimental 

 Farm, after it had been compared with steam for the same purpose. Formalin gives 

 very good results with greater economy and, with the exception of the first year, when 

 the mould was not treated, we have never noticed any disease in the seed-beds. It 

 should be added, however, that few planters care for their mould as well as is done 

 here with that delivered to us by the Division of Horticulture. 



The reports of Mr. O. Chevalier, for Quebec, and of Mr. W. A. Barnet, for Ontario, 

 give in greater detail the results of the work at the Stations under their charge. It 



