220 Journal of Agricultural Research voi. xvi, no. s 



spora nicotianae E. and E.)- The heaviest spotting was found on the top 

 and middle leaves, while the bottom or sand leaves were but slightly 

 affected. Frogeye, on the contrary, is found chiefly on the sand leaves. 

 The field evidence indicated that the vertical distribution of the spots 

 on the plants was determined by their stage of growth at the time of 

 infection, and that leaves which had attained a certain stage of growth 

 were not susceptible to infection. In some fields the infection was 

 heaviest on the top leaves and in others on the middle leaves. Fre- 

 quently the spots were found to be most numerous on one side of the 

 plants, indicating the probable dissemination of the inoculum by wind- 

 blown rain. 



The consensus of the statements of the farmers placed the first appear- 

 ance of the spotting between the third and fourth weeks in July, follow- 

 ing a protracted period of rainfall. The tobacco at this time was at 

 about the stage for topping. No one had seen any of the spotting earlier 

 in the season, and there had been no evidence of it in the seed beds. One 

 farmer who had planted two fields from the same seed bed stated that 

 the disease was much worse in the field on new ground than on old ground. 

 There was no evidence from any source that continuous cropping with 

 tobacco, as practiced on many farms, had been conducive to heavier 

 infection. 



Some of the farmers had been troubled with the disease in the previous 

 year, 1916, and a few stated that they had seen it occasionally over a 

 period of 10 or 12 years, but never so generally destructive as in 191 7. 

 Prof. T. B. Hutcheson, of the Virginia Experiment Station, informs us 

 that he has known this spotting in Charlotte County for 12 or 15 years. 



Opinions among the farmers as to the cause of the disease were cen- 

 tered on the wet weather, the fertilizer, especially the supposed deficiency 

 in potash, and the seed. The disease was found on both the flue-cured 

 and sun-cured types of tobacco, and no differences in the susceptibility 

 of varieties were apparent. 



Evidence that the disease is not occasioned by lack of potash and that it 

 is not a fertilizer phenomenon, except in a secondary way, was obtained 

 from a study of the distribution of the spotting on the fertilizer plots at 

 the experimental substation at Charlotte Court House. Early in Sep- 

 tember the disease was prevalent on all plots which had received appli- 

 cations of acid phosphate alone or in various combinations with sulphate 

 of potash and nitrate of soda. It was the opinion of several observers 

 who went over these plots that they were uniformly spotted. None of 

 the spotting was present, however, at this time, on any plots which had 

 had no applications of phosphorus and which had received only nitrate 

 of soda or sulphate of potash, or both. There was no spotting on the 

 control plots. The tobacco plants on those plots which had received 

 phosphorus were larger, more vigorous, and matured three weeks 

 earlier than those which had had no phosphorus. The superintendent of 



