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TOBACCO 153 



the soil or fertilizers, but excessive nitrates are said to 

 favour its development. In India it is also said not 

 to occur on newly-cleared jungle lands. It is not 

 transmitted through the seeds, but on general principles 

 it is inadvisable to use seeds from unhealthy plants. 



The only satisfactory remedies are preventative 

 measures, such as careful preparation and care of the 

 seed beds, the selection of clean healthy plants, careful 

 field cultivation, care in handling, and so far as possible 

 protection from insects. 



Leaf Spots. Tobacco, like most plants, is affected 

 with various fungi which attack the leaves and produce 

 spots, and since the leaves are the commercial parts, 

 injuries are much more serious on the tobacco than on 

 most plants. The amount of injury due to these causes 

 depends upon the season ; being much greater in a 

 very wet than in a relatively dry season. 



The following are among the most important : 



(a) Gercospora nicotianae, E. and E., is one of 

 the leaf-spot fungi which is quite common in the West 

 Indies and the United States, Ceylon, and Sumatra. 

 It is more prevalent on the lower than on the upper 

 leaves, due to the fact that the upper leaves are better 

 aerated and receive more sun while the lower leaves 

 retain the moisture. It is more troublesome in the 

 Western than in the Eastern Hemisphere. 



(b) Gercospora raciborskii occurs in Queensland, 

 Ceylon, and Java, and behaves in much the same 

 manner as the preceding, while an undetermined species 

 has been reported from Dumbara as causing a leaf 

 disease locally known as " pulli." 



(c) Ascochyta nicotianae, Pass, is another of these 

 leaf-spot diseases which occurs in the West Indies, but 

 is not so severe as C. nicotianae. 



(d) Macrosporium tabacinum, E. and E., is the 

 cause of a leaf-spot known as " white speck." It causes 

 small, circular, rusty red or brown spots which later 

 develop ashy-coloured centres. 



(e) Macrosporium longipes, E. and E., causes the 



