BIENNIAL REP( RT, ]»27 AND 1928 307 



Acetic acid used as a soil disinfectant in tobacco seed-beds infested with 

 Tliielavia and "daniping-off" fungi has given excellent results. This treat- 

 ment has been applied to a number of commercial beds and considerable 

 data should be available in 1929. 



As a corollary of this feature of the work, acetic acid was tried as a 

 soil disinfectant for the control of damping-off of red pine seedlings in a 

 forest nursery. Very promising results were obtained. 



Both monochloracetic acid and formic acid failed to prevent infection of 

 tobacco by Thielavia. 



Yield of tobacco on limed plots was much less than on similar plots 

 whicii had been acidified by either sulfur or sulfuric and orthophos- 

 ])horic acids. 



riiosphoric acid alone was found to favor black root-rot as does lime. 

 Since both of these substances are known to inactivate aluminum in acid 

 soils experiments have been undertaken to determine whether ahiminum 

 may be in part responsible for the inhibition of Thielavia in acid soils. 



i'ot experiments were conducted during the winter of 1926-1927 to 

 determine the effect of lime on tobacco in the absence of Thielavia. 

 Lime in tlie presence of Thielavia was associated with a loss in yield of 

 tobacco; lime in the absence of Thielavia was associated with a decided 

 gain, which indicates that lime in the absence of Thielavia is beneficial to 

 tobacco. 



In experiments conducted to determine the effect of soil temperature 

 oil the response of tobacco to lime in the absence of Thielavia, it was 

 found that the greatest benefit from lime was at soil temperatures of 24° 

 to 8()°C. At soil temperatures of 20° to 15°C lime actually retarded 

 growth of tobacco. 



On the basis of the sorting record and burn tests of the tobacco grown 

 on tiie Tillson Farm plots in 1927 it was concluded: that the quality was 

 much poorer on plots with too much lime than on plots with no lime; 

 that the quality on limed plots was improved by the application of acid- 

 ifying chemicals to the soil; that lime or the absence of lime did not signifi- 

 cantly affect fire-holding capacity of the leaf, and that the fire-holding 

 capacity of the leaf from limed plots was improved by certain acidifying 

 treatments of the soil. 



No infection of alfalfa by Thielavia was found in limed plots known 

 to be infested with this fungus. Alfalfa does not appear to be a common 

 host of this fungus, and were it not for brown root-rot alfalfa probably 

 could be safely rotated with tobacco. Severe brown root-rot occurred on 

 tobacco which followed alfalfa, timothy, or alsike clover. 



Brown Root-Rot. The occurrence of brown root-rot on tobacco grown 

 on soil in which a cover crop of timothy has been turned imder and be- 

 come partially decomposed is a matter of common observation. This 

 suggested a study of the effect on tobacco roots of timothy infusions of 

 different ages applied to the soil. 



Wiien such infusions were applied to soil in which tobacco plants were 

 growing, the effect on the tobacco was found to be sometimes harmless 

 and sometimes very injurious depending on the age of the infusions, that 

 is, on the stage of the decomposition of the timothy. The response of 

 plants to an infusion of a given age was influenced b}' the proportion of 

 tops to roots of timothy tised or by the temperature at which the de- 

 composition process went on. These infusions of timothy which retarded 

 the growth of tobacco plants produced on their roots brown discolora- 

 tions and lesions apparently of the same type as those which, in the field. 



