14 



BULLETIN 1256, U. S. DEPARTMENT OF AGRICULTURE. 



Cause. — Granville wilt is a bacterial disease, and the organism 

 concerned has been named Bacterium solanaa varum. This parasite 

 causes similar destructive rots of tomatoes and potatoes, being cap- 

 able also of attacking many other plants. The bacteria pass through 

 and multiply particularly in the woody vessels of the plants, thereby 

 clogging or otherwise injuring these vessels, so that the water and 

 food supplies are cut oif and the plant naturally wilts and gradually 

 dies. 



The germs live over winter in the soil or in the decaying roots 

 and refuse of preceding crops for at least four or five years. In the 

 yearly presence of tobacco or any other plant on which the bacteria 

 can live the disease, of course, continues to infest the soil indefinitely 

 instead of gradually dying out. The organism may be spread from 

 Held to field in various ways like any other soil-infesting parasite, 

 but its spread is more frequent through direct transfer of soil from in- 

 fested fields, as carried by men, animals, water, tools, or other equip- 



Fig. 8. — A field of tobacco plants affected with Granville wilt. The symptoms shown 

 here, accompanied by blackening in the woody layer of the stalk, which yields an 

 ooze on pressure of the cut end, are typical of this disease. 



ment, and these facts should be borne in mind when new land is being 

 used for tobacco. 



Conditions favoring the disease. — Granville wilt seems to be es- 

 pecially favored by hot weather. Dry weather usually exaggerates 

 the disease symptoms, in that it hastens the drying up of the plants ; 

 but as a matter of fact wet weather and wet soils are more favorable 

 for actual disease development. Sandy soils are apparently more 

 likely to become heavily infested than clay soils. Wounding of the 

 roots markedly favors infection, and a certain amount of this is un- 

 avoidable in transplanting and cultivating. Nematodes, which cause 

 the root-knot disease, are common in the wilt-infested districts, and 

 it seems that wounding of roots by these organisms greatly favors 

 infection by the wilt organism. 



Control. — The control of this important disease in the badly in- 

 fested area lies in crop rotation. A number of other methods of 

 control have been tried, among them resistant varieties and various 



