TOBACCO DISEASES AND THEIR CONTROL. 



25 



marked. As far as known, broom rape is largely limited to Kentucky 

 tobacco fields, especially in the White Burley district, although it has 

 been known to occur on tobacco in other States. The infested area 

 seems to be limited to the hemp-growing district, the same broom 

 rape being also parasitic on hemp. The seeds are commonly mixed 

 with hemp seed and are sown with it ; hence they infest the soil upon 

 which tobacco is subsequently planted. 



A large number of species of broom rape are known, especially 

 in foreign countries. The common species in the Kentucky fields is 



Orobanche ramosa. 

 Aside from tobac- 

 co, this species also 

 attacks hemp, to- 

 mato, potato, rape, 

 cabbage, and pars- 

 nip ; but corn, cere- 

 als, grasses, and 

 legumes as a class 

 are immune to this 

 species. The con- 

 trol of the trouble, 

 therefore, is largely 

 based on crop rota- 

 tion, using plants 

 not susceptible to 

 attack on infested 

 land for several 

 years before re- 

 planting to tobacco 

 or other crops, 

 where such precau- 

 tions are deemed 

 necessary. 



LEAF DISEASES. 



WILD-FIRE. 



Description. — A 

 serious outbreak of 

 an apparently new 

 disease which be- 

 came known as 

 wild-fire occurred 

 in North Carolina 

 in 1917. This disease has since become introduced into practically all 

 tobacco districts. The occurrence of wild-fire is more or less sporadic, 

 being markedly influenced by weather conditions, but the seriousness 

 of the disease, under conditions favorable for its spread, is well estab- 

 lished by the large losses which it has caused since its recognition. 



Wild-fire may attack plants at almost any stage of growth, and 

 so far as is definitely known all field infection originates from in- 

 fected seed beds. The most typical symptoms in the plant bed as 

 well as in the field are on the leaves in the form of spots which are 



Fig. 17. — Later 



stages of development 

 tobacco. 



of broom rape on 



