MOSAIC OF SUGAR CANE AND OTHER GRASSES, 21 



produce diseased plants and that careless importation of seed is 

 apt to result in increased amounts of the disease. 



In the Hawaiian Islands also the disease is controlled by selection 

 of clean seed and the use of resistant varieties. 



Measures for controlling the mosaic disease recommended in the 

 following pages are not haphazard expedients, but have been used 

 with very satisfactory results in Porto Rico for more than a year. 

 Planters there have paid a heavy price to learn them, and it is urged 

 that planters of sugar cane in the United States cooperate to prevent 

 a possible epidemic. Indifference to the situation may result in the 

 cane growers being confronted with the fact that it is too late to prac- 

 tice seed selection, as is already the case in western Porto Rico. 

 At present, it will work no particular hardship on the planters to 

 take steps that will reduce the disease to a minimum. 



ELIMINATION BY ROGUING. 



Roguing consists of pulling out infected plants, root, stem, and 

 branch, and throwing them down between the rows. It is based on 

 the fact that as soon as the plants are wilted they are no longer 

 dangerous as a source of infection. This method is applicable only 

 to fields in which the disease has not obtained a strong foothold. 

 It is not recommended for fields in which the number of infected plants 

 exceeds 5 per cent in half -grown to mature cane or 20 per cent in young 

 plants just sprouting. The size of the field and the condition of 

 surrounding fields with reference to the occurrence of the disease 

 in them must also be taken into consideration. When the field is 

 quite small or consists merely of a few rows or plants of a new variety 

 being propagated for trial on a plantation scale, it should be rogued 

 even if 100 per cent of the plants are infected. Such plants are a 

 constant menace to plants in surrounding fields. In large fields 

 where the proportion of diseased individuals is greater than 20 per 

 cent, roguing is impracticable, not because the plants are any less 

 potent as sources of infection, but because diseased plants produce 

 millable cane, and to destroy considerable quantities of such plants 

 would probably result in greater financial loss than would be sustained 

 by the reduction in yield due to new cases. Large fields with a high 

 percentage of diseased plants should be allowed to mature, but no 

 cane from such fields should be saved for seed. 



It is suggested that the following schedule of inspections and 

 roguing be put into operation: In the spring, just as soon as all of the 

 plants have sprouted, the fields should be inspected by passmg up 

 and down the rows. All diseased stools should be pulled out of the 

 ground and cast down between the rows. If this first inspection is 

 carried out in a thorough manner the field will be completely freed 

 from the disease provided no secondary infections are going on. 



