May IS. I9J9 Influence of Soil Environment on Rooirot of Tobacco 45 



does much damage. No definite experimental data are given, however, 

 in support of these views. The following year (1908) drouth is said to 

 have reduced the injury due to the disease. 



Briggs (j) reported, upon evidence obtained from Connecticut soils 

 that the fungus attacks are most severe on soils made alkaline by large 

 applications of lime, ashes, or fertilizers containing carbonate of potash, 

 and that the alkaline condition in infested soils should be corrected by 

 the use of acid fertilizers in order to obviate the damage by T. hasicola. 

 This advice was received favorably by both practical growers and sci- 

 entists, and many recommendations were based upon it. 



Gilbert {12) concludes that an abundance of humus, a considerable 

 percentage of clay, high fertilization either with chemicals or manure 

 (expecially nitrogenous fertilizers), excessive water, and high tempera- 

 tures favor the disease. In an experiment to determine the influence 

 of the amount of watering he found that excessive water increased the 

 disease, although 62 per cent of the plants in the scantily watered beds 

 were diseased. He also compared the yield as a result of transplanting 

 diseased and healthy plants in the field, using a "Havana Broadleaf " 

 variety. He obtained as good yield from the diseased plants as from the 

 healthy ones. 



Whetzel and Osner (27) recommended acid-phosphate fertilization for 

 the control of T. hasicola which causes fiber-rot on ginseng. 



Benincasa (2) reporting on results obtained in comparing different 

 "soils" for growing tobacco plants, recommends sand or "pozzolano" 

 a volcanic ash for this purpose, since favorable conditions for disease 

 are said to be absent in these . He also states that T. hasicola is a weak 

 parasite under certain conditions. 



Martinazzoli (18), however, reported that he obtained T. hasicola 

 from beds where pozzolano was used, infection probably having come from 

 soil. 



Massee (jp) concludes that T. hasicola can not infect host plants in 

 pure sand, since the fungus is able to infect only in the presence of 

 organic matter which will permit the mycelium to exist for some time 

 as a saprophyte. 



Chittenden (7) had difficulty in obtaining infection with T. hasicola 

 until overwatering of the soil was practiced. 



Rosenbaum (22) believes that such external conditions as excessive 

 water, lack of aeration, and heavy manuring favor infection. 



Reddick (21) reported unsatisfactory results for the control of 

 Thielavia of violets by acidifying the soil with acid phosphate as recom- 

 mended by Briggs. Stable manure apparently did not act deleteriously 

 on infested soil. The experiments were not carried far enough, however, 

 to be entirely conclusive. 



The present writer (14), as a result of field observation, also believed 

 soil moisture to be the main controlling factor in determining the severity 

 of the disease. 



