Vegetable and Field Crops 253 



become brown or black, and the entire root system is in- 

 volved later. The decayed roots are brittle and break 

 easily. Numerous lateral rootlets are put out to replace 

 them, but these also succumb sooner or later. The leaves of 

 diseased seedlings on rich soil are usually abnormally dark 

 green. They may, however, in poor soil be of a sickly yellow 

 color. 



In the field the diseased seedlings may remain without 

 growing for weeks; some yellowing, wilting, and dying. 

 Others in light soil may survive and yield a fair, but late, 

 crop; in heavy soil few survive to be of value. When large 

 roots are attacked, the effect is generally limited to the outer 

 surface, where a brownish, scurvy appearance is produced. 



Sick plants in uninfested soil or healthy plants set in in- 

 fested soil result in diseased crops, and the development of 

 the disease when the causal fungus is present is favored by 

 alkaline fertilizers. 



To avoid loss, only uninfected plants from a clean seed 

 bed should be used. A seed bed can be rendered safe and 

 so maintained by disinfection, by the means suggested 

 on page 460, selecting the method best applicable to the 

 conditions. Surface firing is the method most widely used in 

 connection with the tobacco crop. Formalin and steam have 

 also proved efficient in many instances. 



The following measures conduce to reduction, though 

 not to complete eradication of the disease: the use of light 

 rather than heavy soils for the seed bed ; avoidance of excess 

 of water or fertilizer; the use of a new bed each year; avoid- 

 ance of too heavy seeding. Infested fields should be given a 

 rotation of nonsusceptible crops. A strain of white Burley 

 has been developed to a state of high resistance. 



Granville-wilt -°' ^''^' ^'^^' ^^^' ^"^^ (Pseudomonas solanacearum 

 (EFS.) ). — This wilt was first noted in print in 1903 

 though known to tobacco growers in Granville County, N. C, 

 as early as 1881. It takes possession of the soil, prohibiting 

 successful tol)acco culture in succeeding years, and in sections 

 where tobacco is the chief, possibly the only profitable money 



