BULLETIN OF THE 



No. 40 



Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief, 

 January 15, 1914. 



THE MOSAIC DISEASE OF TOBACCO. 1 



By H. A. Allard, 

 Assistant Physiologist, Tobacco and Plant-Nutrition Investigations. 



INTRODUCTION. 



" Mosaic " is one of the most serious and widespread diseases known 

 to affect the tobacco plant. This disease also is known locally as 

 " calico," " gray-top," " mottled-top," " mottling," and " foxy " to- 

 bacco. Especially in southern tobacco sections the term " frenching " 2 

 is used to designate abnormal, sickly plants characterized by the de- 

 velopment of stringy, very thick, and leathery leaves which may be 

 free from mottling. It has not been determined whether this is dis- 

 tinct from mosaic or only a somewhat different phase of this 

 disease. In the tobacco sections of Kentucky and Tennessee "Wal- 

 loon" is often used to denote mosaic or other abnormal appearances 

 more or less closely resembling symptoms of the mosaic disease. The 

 disease has also been termed "chlorosis." Finally, mosaic plants 

 sometimes are spoken of as "brindle" or "mongrel." These terms 



1 In a study of the mosaic disease of tobacco facts have been learned which throw con- 

 siderable light on its nature and origin. It has been shown that it is communicable to 

 plants of many genera of the solanaceous family and that aphides are sometimes active 

 disseminators of infection both in the greenhouse and in the field. The fact that par- 

 ticular insects are involved in the spread of the disease not only helps to explain the 

 contradictory results obtained by previous investigators, but also serves to indicate 

 means by which the disease can, to a greater or less extent, be controlled under practical 

 field conditions. 



Since insects are involved in the spread of the mosaic disease both in seed beds and 

 in the field and the practical control of this disease must depend primarily upon an 

 intimate knowledge of the habits and distribution of species which may act as capable 

 carriers of infection, this phase of tbe investigation has been taken up in cooperation 

 with the Bureau of Entomology. — Wm. A. Taylor, Chief of Bureau. 



2 The term " frenching " or " frenched " is applied to sickly, spindling corn plants 

 and peach trees -as well as to tobacco plants. Its origin dates back to the settlement of 

 Maryland when the English settlers applied the term " Frenchmen " to weak, spindling 

 tobacco plants as a term of contempt. See Clayton, John. A Letter ... to the Royal 

 Society, May 12, 1688, giving an account of several observables in Virginia ... p. 19. 

 (In Force, Peter. Tracts and Other Papers, Relating Principally to the Origin, Settle- 

 ment, and Progress of the Colonies in North America, v. 3, Washington, 1844.) 



13128°— Bull. 40—14 — -1 



