TOBACCO DISEASES AXD THEIR COXTROL. 



13 



ing of diseased plants until all healthy plants have been handled. If 

 decayed pith is touched by the worker's hands they should be cleaned 

 before continuing work on healthy plants. 



GRANVILLE WILT. 



Description. — This disease was first found in Granville County, 

 N. C, and' is therefore commonly referred to as Granville wilt, 

 although it is often referred to 

 simply as tobacco wilt. It is also 

 known to occur in tobacco districts 

 of Virginia, Florida, and Georgia 

 as well as in foreign countries. Al- 

 though the disease has been a se- 

 rious one for a long time, particu- 

 larly in Xorth Carolina, it has not 

 and probably never will become so 

 in the more northern tobacco dis- 

 tricts, on account of the fact that it 

 thrives well only under relatively 

 high temperature conditions The 

 disease has made a considerable 

 though not a rapid spread in the 

 southern districts. Fields ordinar- 

 ily become gradually infested, so 

 that under repeated cropping to 

 tobacco practically complete crop 

 failure results. 



The plants ordinarily are first in- 

 fected through the roots from in- 

 fested soil. Subsequently the dis- 

 ease affects the stems and leaves. 

 Usually the symptoms first appear 

 two to four weeks after transplant- 

 ing, the number of wilting plants 

 gradually increasing. The first 

 characteristic sign of the disease 

 on a plant is the drooping of one or 

 more leaves, followed by distortion 

 or wrinkling, yellowing, and finally 

 browning and drying up (fig. 8). 

 If the tobacco stalk is cut across in 

 an early stage of the disease, the 

 woody portion will show yellowed 

 streaks, which in later stages turn 

 to brown or black as contrasted with 

 the normal white tissue. In late 

 stages of the disease parts or all of 

 the surface of the stalk turn black 

 and the pith also rots out, accom- 

 panied by a decaying root system. 

 The cut ends of the stalks or mid- 

 ribs when pressed yield a dirty 

 white ooze, which is characteristic and aids in distinguishing it from 

 certain other wilt diseases. 



Fig 



-Hollow-stalk 



of tobacco pro- 

 duced by inoculation. If the bacteria 

 causing this disease are inserted into 

 a stalk they cause a rot, as shown in 



this split stalk. 





