BLACK ROOT-ROT OF TOBACCO 



12.5 



fact that a similar difference was not apparent on tiie uninoculated iialf 

 indicated that the dwarfing effect was due to the influence of lime on the 

 root-rot. When the roots were examined it was found that (1) the disease 

 was very bad on all the inoculated limed plots, (2) the lesions were fairly 

 prevalent on the roots of the unlimed inoculated plots (hut nuich less so than 

 on the limed plots), (3) there were frequent lesions on the uninoculated limed 

 plots, and (4) only rarely could a lesion be found on the uninoculated, un- 

 limed plots. 



The results noted in 1923 may be summarized as follow.'.: In the inoculated 

 half of the held, the yield on limed plots was 16 per cent less than the yield 

 on imlimed plots. In the uninoculated half of the field, the jield on limed 

 plots was still 7 per cent more than the yield on unlimed plot.s, but this was 

 a drop of 12 per cent from the previous year. On the inoculated half of the 

 field even the unlimed plots suffered some loss from black root-rot, the yield 

 being about 8 per cent less than on unlimed plots in the uninoculated part 

 of the field. 



In 1923 there was a small loss from the use of timothy, and, as in the pre- 

 ceding year, this loss was less on the inoculated than on the uninoculated plots. 



Season of 1924 



It became apparent early in the season that tlie limed plots were making a 

 much poorer growth than the corresponding unlimed ones. This was particu- 

 larly striking on the inoculated half, but it was also quite apparent from the 

 poor growth that there were many places in the uninoculated half where root 

 rot was doing serious danage. It was plainly evident that root-rot was no 

 longer confined to the inoculated end of the lime strips but that it was now 

 present even to the extreme opposite end. A second very ajjparent fact was 

 that there were some very good plots of tobacco (unlimed) in the inoculated 

 part of the field, .showing that the effect of very thorough inoculation was 

 not lasting when the soil condition was not right. These observations during 

 the growing season were substantiated by examination of the roots after the 

 crop was harvested. It was then found that, irrespective of inoculation, the 

 number of lesions was very small on all plots which had not been limed. On 

 the limed .strips, lesions were particularly numerous on the roots from the 

 inoculated plots; but many of the roots from the other end were in just as 

 serious condition, while others were relatively free. This indicated that on 

 the uninoculated limed plots, the infestation was still uneven. Nevertheless 

 it seemed to be spreading rapidly in these. The cured weights per acre as 

 given in Tables I and II showed a loss from liming of 17 per cent on the 

 inoculated plots and 12 per cent on the uninoculated plots. 



In 1924, the fourth year of the experiment, the loss from black root-rot on 

 limed plots was more severe than in the previous years, although no lime was 

 applied this year. 



In the unlimed plots, the amount of root-rot was small, whether or not the 

 plots were inoculated. The yield on the inoculated plots was only 4 per cent 

 less than on the corresponding iminoculated plots. 



For the third successive year a reduction in yield was associated with the 

 use of the timothy cover crop. 



