THE BROWN ROOT ROT OF TOBACCO AND OTHER PLANTS 



caused by any other agency or condition interfering with the food 

 or water supply of the plant. 



The symptoms on the root system are more characteristic. Where 

 the disease is extensive the plant is easily pulled from the soil, and 

 the few remaining roots on the base of the stalk are brown and 

 decayed; or, as is frequently characteristic in moderately stunted 

 plants later in the season, a considerable number of well-developed 

 roots with distinct lesions may be present in the uppermost layer of 

 soil, but the taproot and strong secondary roots normally present in 

 the deeper layers of soil are either lacking or have made little or no 

 growth. These conditions might be mistaken for Thielavia root rot 

 except for the absence of black lesions and spores of Thielavia. 

 (Fig. 3.) Their absence in the presence of a root decay is one of 

 the principal diagnostic characters for brown root rot. In both 



Fig. 2. — A diseased field of Havana tobacco at Deerfield, Mass., showing character- 

 istic wilting as a result of a deficient root system. The symptoms on the roots 

 were typical of brown root rot 



diseases the plants are apparently stimulated to send out more new 

 roots than would otherwise develop from the portion of the stalk 

 below the surface of the soil. These may or may not make con- 

 siderable headway into the soil before being destroyed. The roots 

 which are able to persist are on the average generally nearer the 

 surface than the main fibrous roots of a normal plant. 



So far as known the plants never actually die as a result of brown 

 root rot but may remain throughout the entire season without mak- 

 ing much growth. On the other hand, they may show a decided 

 tendency to recover late in the season. 



Brown root rot is not ordinarily distributed uniformly over large 

 field areas. So far as observation has gone, the disease in its most 

 serious form is often more or less limited to spots in the field; at 

 other times, the whole field may be very uniformly affected except 

 for occasional small spots of good tobacco. The lack of uniformity 



