8 BULLETIN 829, U. S. DEPARTMENT OE AGRICULTURE. 



each successive year. The figures in Table II were ob tamed by 

 cutting all of the cane hi approximately square patches of about 

 one-tenth to one-fifth of an acre selected in commercial fields and 

 in the fields at the Sugar Experiment Station, Audubon Park, La. 

 The stalks cut from such patches were then sorted into two classes, 

 diseased and healthy, and the average weight of stalks in each class 

 was determined. The patches were not selected at random, but an 

 attempt was made to find areas where the mosaic was doing a maxi- 

 mum amount of damage and at the same time a sufficient number of 

 healthy plants were present in the patches, growing under identical 

 conditions, in order to make a fair comparison possible. Since, if 

 no attempt is made to control the disease in these fields, we may 

 expect ultimately to find an infection of 100 per cent, the losses will 

 then be equivalent to the figures found in column 5 of Table II. 



Table II. — Tests of sugar cane in Louisiana, showing the extent of losses in different 



varieties. 



Variety. 





Average weight of 



Reduc- 







stalks — 



tion in 



Diseased 







weight of 

 diseased 



stalks in 

 field. 











Healthy. 



Diseased. 



Healthy. 



Diseased. 



stalks. 









Pounds. 



Pounds. 



Per cent. 



Per cent. 



330 



160 



1.13 



0.7 



38 



32 



268 



100 



1.507 



1.22 



19 



27 



204 



108 



1.27 



1.03 



18 



34 



348 



136 



1.65 



1.16 



29 



28 



373 



310 



.874 



.787 



10 



45 



Loss in 

 tonnage. 



Louisiana Purple. 

 Louisiana Striped 



D-74 



D-95 



L-511 



Per cent. 

 12.16 

 5.13 

 6.12 

 8.12 

 4.5 



PRIMARY SYMPTOMS. 



Upon walking between the rows of cane in an affected field, more 

 or less plants will be seen that are conspicuous on account of a gen- 

 eral pallor of the leaves. This may be discernible for many rods. 

 Closer examination of such plants reveals that the pallor is due to 

 irregular light-colored streaks or spots on the leaves. The affected 

 leaf areas, in so far as color is concerned, are of two distinct types. 

 The most common type presents merely a " washed-out" appearance. 

 It is, in fact, merely a tint of the normal color, in which the blue and 

 yellow are present in the same proportions but diluted. In the sec- 

 ond type, the yellow is predominant, and the affected areas have a 

 decided yellowish green appearance. The normal and affected areas 

 are sharply demarked. In other words, there is no gradual merging 

 of one color into the other. There is a great diversity of patterns 

 in the different varieties, due to the variation in the amount, size, and 

 shape of the light-colored areas, but the arrangement is so constant 

 in any particular kind of cane that the character could be used as an 

 aid in determining; varieties. 



