12 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE. 



able. It is possible to recognize such fields from a distance of half a 

 mile or more on account of their sickly, dry appearance. 



INJURIES RESEMBLING MOSAIC. 



Many types of injury are commonly found on cane leaves that 

 might be confused with this malady by one not familiar with it. 

 The condition termed chlorosis, which is due for the most part to 

 soil conditions, expresses itself in many ways, some of which closely 

 simulate the mosaic disease. The affected areas are white opaque 

 or yellow, and the most familiar form is a regular striping of the leaves 

 longitudinally. The stripes usually extend the entire length of the 

 leaves and may be about one-eighth of an inch wide and numerous, 

 with normal green stripes of equal width spaced between them, or 

 the chlorotic areas may be quite wide. Occasionally, the entire leaf 

 is pure white. Less frequently the areas are in the form of large 

 spots or blotches, extending inward from the margins of leaves or 

 situated at the center of the blades anywhere from base to tip. 

 Another type, which is rare, consists of a very fine irregular white 

 mottling of the leaves, which, however, is in local patches and does 

 not involve the whole leaf, as is invariably the case with the mosaic 

 disease. Many fungi cause spotting of the leaves of cane, but these 

 can easily be distinguished, as the spots usually turn brown and the 

 leaf tissue dies, which does not occur in the cane mosaic. Since a 

 pale-green halo is sometimes present surrounding these small spots, 

 they have the appearance of mosaic from a distance, especially 

 when quite numerous, but a close examination always reveals quite 

 distinct differences. Many insects, especially those which feed by 

 puncturing the leaf epidermis and sucking the sap from the layers 

 of cells below, cause a very fine mottling of the leaves when the 

 punctures are present in enormous numbers. Ordinarily, the punc- 

 tures are scattered and can lead to no confusion. This type of in- 

 jury can also be determined by close inspection, since the minute 

 pale area surrounding each individual puncture is almost exactly 

 circular and has no tendency to elongation in the direction of the 

 long axis of the leaf, such as is almost invariably the case in true 

 mosaic. Drought, lack of proper nutrients in the soil, excessive 

 rainfall, and poor tilth, or combinations of these, sometimes result in 

 a general pallor or yellowing of the leaves, but this color is always 

 uniform and can lead to no confusion. 



VARIETAL SUSCEPTIBILITY. 



VARIETIES ATTACKED. 



More than a thousand varieties of cane have been determined to be 

 susceptible to the mosaic disease. Most of these are the progeny of 

 seedling canes that exist in small variety-test rows or patches at the 



