BLACK ROOT-ROT OF TOBACCO |j9 



cure sufficient water and soil nutrients for normal growth of the above ground 

 parts of the plant, hence the dwarfed slow growth and "flagging"' on hot days. 

 Black root-rot may also occur in the seed-beds, where it exhibits the same 

 symptoms, viz., slow growth, yellow or "black" color of leaves, "flagging," 

 and black rotted roots. Many of the plants also die. The beds look very 

 uneven. 



Previous Investic.ations 



In the first experiment station publication which recorded and described 

 the disease in the Connecticut Valley, Jenkins and Clinton (5:7)3 stated: 



"It is not definitely known whetiier an acid, alkaline or a neutral soil is 

 best adapted to the growth of the fungus, which we know can grow in the soil 

 itself apart from the tobacco root, but it is reasonable to suppose that this 

 factor may have its influence." 



Later (5:8): 



"One of the growers whose fields suffered severely was inclined to lay it to 

 the excessive use year after year of potash fertilizers, which gradually accun)u- 

 lated in the soil, and especially to the use of the carbonate of potash." 



The first, and up to the present date the most important, contribution on 

 the relation of soil reaction to root-rot was a brief circular by Briggs (1) 

 describing results of experiments in Connecticut in 1907. His conclusions ar^ 

 best summarized in the following statements which we quote: 



"The results of the writer's investigations thus far indicate that the tobacco 

 is much more severely injured by tlie fungus on fields where tlie soil has been 

 made alkaline by the long-continued use of large amounts of lime, ashes anf' 

 fertilizers containing carbonate of potash." 



"In all cases it was found that the plots on which carbonate of ])otash wa"^ 

 used gave the smallest plants and the lowest, yields. The use of lime with 

 the carbonate of potash still further diminished the yield. The use of car- 

 bonate of potash and lime with cottonseed meal and ground fish gave a yield 

 of but 900 pounds per acre. This yield was 200 pounds less to the acre than 

 when no fertilizer was used and was only a little more than half the yiel'^ 

 obtained from some of the other plots." 



In pot experiments he found that: 



"In soils free from root-rot, the use of 1 per cent of lime gave a better 

 growth of tobacco than where no lime was used. This shows that the lime 

 does not injure the tobacco directly .... The use of hydro-chloric acid, on 

 the other hand, increased the yield by about 10 per cent although this acid 

 carries no plant food .... The root systems of the plants in all the pots to 

 which lime or carbonate of potash was added were badly diseased .... The 

 roots of the plants grown in acid-treated soil were perfectly clean and white, 

 and entirely free from the fungus." 



All of Briggs' experiments were with naturally infested soils from fields 

 where the soil acidity had been greatly reduced by use of alkaline fertilizers 

 and lime. The reaction of the soil was not determined either before or aftc 

 the treatments which he applied. 



Johnson and Hartman (7:53-60) determined the influence of soil reaction 

 on root-rot by growing plants in pots after adding graduated quantities of 



.3 Numbers in parenthesis refer to bibliography at the end of this bulletin. Num- 

 bers after the colon give the page on which statement referred to may be found. 



