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



just been removed grew without any evidence of the disease. The 

 virus does not live over in the soil and it is doubtful whether it exists 

 there at any time. In this respect the mosaic does not by any means 

 present the practical difficulties in the way of control measures to be 

 met with in root-rot. Root-rot, in fact, is to be regarded as a far 

 more serious problem for the Louisiana cane planter than mosaic on 

 this account. 



RELATION TO DISINFECTANTS. 



Treatment of infected seed pieces by soaking in strong Bordeaux 

 mixture or corrosive sublimate previous to planting has had no effect 

 on the course of the disease. All shoots were typically mottled as 

 soon as they appeared. It was hardly to be expected that superficial 

 disinfection could influence the virility of the infectious principle when 

 all our evidence indicates that the latter permeates the internal 

 tissues, or at least the vascular systems of affected plants. 



RELATION TO FERTILIZERS. 



Many experiments x have been performed in Porto Rico to deter- 

 mine the effect of applying fertilizers, since the claim was made by 

 many planters that mosaic was due to insufficiency of plant nutrients 

 in the soil. Filter press cake, sulphate of ammonia, and lime in 

 various combinations, together with turning under cover crops and 

 good tilth, had no noticeable effect on the disease as compared with 

 control plats. Standard complete fertilizers were also tried. Beyond 

 a slight stimulation in growth and the darker green color of the treated 

 plants, there was no observed effect. Diseased plants may be expected 

 to respond to good growing conditions the same as healthy ones, 

 but the same constant difference between healthy and diseased plants 

 is maintained under all conditions. The diseased stalks remain below 

 the average weight for healthy stalks and are just as capable of 

 spreading the disease. Liming the soil has no more effect on diseased 

 plants than the application of fertilizers. 



CONTROL. 



It is interesting to note that in Java long experience has demon- 

 strated that the disease can best be held in check by careful selection 

 of healthy plants for seed and by replanting fields with cuttings taken 

 from the same field, in preference to buying cuttings of unknown 

 origin or moving the cuttings from field to field on the same plan- 

 tation. The use of such methods practically amounts to tacit 

 admission of the infectious nature of cane mosaic, although it is 

 ascribed to "bud variation." The facts which have most impressed 

 the Dutch planters are that cuttings from diseased stalks always 



1 Stevenson, John A. The "mottling" disease of cane. Porto Rico Insular Exp. Sta. Ann. Rpt., 

 1916-17, p. 40-77, 1917. [Literature] p. 76-77. 



