UNITED STATES DEPARTMENT OF AGRICULTURE 



.J H rn T i * F i V% i. 



In Cooperation with the 



Wisconsin, Connecticut, and Massachusetts Agricultural 



Experiment Stations 



DEPARTMENT BULLETIN No. 1410 



Washington, D. C. 



July, 1926 



THE BROWN ROOT ROT OF TOBACCO AND OTHER PLANTS 



By James Johnson, Agent, Office of Tobacco and Plant Nutrition, Bureau of 

 Plant Industry, and Professor of Horticulture, College of Agriculture. Uni- 

 versity of Wisconsin; and C. M. Slagg, formerly Assistant Pathologist, and 

 H; F. Mtjbwin, Agent, Office of Tobacco and Plant Nutrition, Bureau of Plant 

 Industry 



CONTENTS 



Tage 



Introduction 1 



Symptoms of brown root rot 2 



Historical review 4 



Isolations from diseased roots 6 



Evidence regarding the nature of the 



disease 7 



Plants affected 11 



Page 



Variety and strain tests with tobacco- 13 



Influence of soil conditions 11 



Influence of drying and aeration 16 



Field-plat experiments 17 



Discussion of results 25 



Summary 28 



Literature cited 29 



INTRODUCTION 



During the last 10 years a disease of tobacco which is character- 

 ized by brown and decayed roots has been under observation and 

 the subject of considerable experimental work. This condition has 

 been referred to as brown root rot, to distinguish it from the more 

 generally known black root rot due to Thielavia hasicola (B. and 

 Br.) Zopf. Intensive studies along etiological lines have failed to 

 yield conclusive evidence as to the actual cause of the disease. Al- 

 though most of the evidence points to a parasitic origin, other evi- 

 dence apparently is contradictory to a parasitic hypothesis. The 

 observations over a period of several years, together with the results 

 from rotation experiments reported in this bulletin, show that the 

 occurrence of brown root rot is closely correlated with the preceding 

 crops grown on the land. Tobacco grown on sod is commonly most 

 markedly affected, and the use of winter cover crops may bring on 

 a similar condition. From an agronomic standpoint as well the 

 problem becomes very complex, since the kind of preceding crop, the 

 soil type, the environmental conditions, and other circumstances 

 determine the occurrence and the severity of the disease. 



So far as is known, brown root rot is most prevalent in the tobacco 

 soils of the Connecticut Valley. A similar condition is known to 

 exist in Wisconsin, Maryland, Kentucky, and in several other tobacco- 

 growing districts, but in the absence of a known parasite or other 

 causal agency it is not readily demonstrable that the conditions ob- 

 served are all due to the same cause. 



87761—26 1 



