26 



BULLETIN 1256, U. S. DEPARTMENT OF AGRICULTURE. 



usually circular, of a bleached or yellowish color (chlorotic area or 

 halo), and often as large as a dime (PL VII, fig. 1). In the center 

 of each spot is a dried area often only the size of a pin point, but 

 varying in size up to as much as half an inch in diameter. The 

 chlorotic area may consequently be only a narrow border or entirely 

 lacking, depending upon the age of the spot and other conditions. 

 These spots when numerous may run together, forming irregular 

 areas and sometimes causing the whole leaf to collapse and dry up. 

 In other cases the bleached or chlorotic area may spread into and 

 throughout an entire leaf, apparently from a center of infection in 

 or near the bud or stem of the plant. Such plants usually fail to 

 make satisfactory growth. 



WW - ■" •• * '* • -^ 



W 



*V* . '^^B 







iv. .•■ ■ , '. * y* * » ** 



E %> *\ * •*> *** -•%' * 



R.\^- 





•j 







I s " -1 



I 



1 







Fig. 



18. — Tobacco leaves showinsr wild-fire. Affected leaves finally become more or 

 less ragged and may often be made practically worthless. 



The bottom leaves are most likely to become heavily infected, not 

 only because they are exposed to infection for a longer period of 

 time but also because they are in a. more favorable environmental 

 position for infection (fig. 18). Under favorable conditions for 

 infection, however, the disease may spread to the uppermost leaves 

 on the plant and even to suckers and seed pods. Cigar wrapper and 

 binder tobaccos especially may be rendered worthless for the pur- 

 poses for which they are used by a comparatively few infections pet- 

 leaf, while other types may not be seriously damaged unless the spots 

 are sufficiently numerous to markedly affect the color of the leaf 

 or cause such extensive drying up in the field as to render harvesting 

 impossible without much breaking, thereby lowering the yield and 

 producing a ragged crop. 



