22 BULLETIN 829, IT. S. DEPARTMENT OF AGRICULTURE. 



Since there are as yet no certain means of determining the latter 

 fact, a second inspection is essential. It should be made from 25 

 to 30 days after the first, a lapse of time sufficiently in excess of the 

 incubation period for mosaic to insure recognition of the disease in 

 plants inoculated prior to the iirst inspection. If no diseased plants 

 are found during the second inspection, it can be assumed that 

 secondary infection is not in operation and that the remaining 

 plants will continue healthy. If diseased plants are found, how- 

 ever, it establishes the fact that secondary infections are going on. 

 The field should be rogued as before, and a third inspection made 

 after the same interval, i. e., 25 to 30 days. If the carriers remain 

 active it may be necessary to repeat the process several times, and 

 owing to the impossibility of recognizing the disease in inoculated 

 plants before the end of the incubation period it is certain that 

 plants which have become infected just before the inspection is 

 made will escape detection. This emphasizes the necessity for 

 making the first inspection early, preferably before leafhoppers or 

 other sucking insects have appeared on the plants. 



This procedure may result in perfect control or eradication of the 

 disease or in partial control, the element of uncertainty being due to 

 our inability to control the carriers. By it their activity can be 

 rendered less effective by reducing the sources of inoculum to a 

 minimum. It has effectually halted the progress of the disease into 

 new territory in Porto Rico. 



ELIMINATION BY GRINDING ALL CANE AND SECURING CLEAN SEED. 



In badly infested sections the problem is manifestly complicated. 

 Where 25 to 60 per cent or more of the plants in large fields are 

 diseased, roguing is obviously out of the question. Such plantings 

 should be allowed to mature. Every stalk of it should be ground, 

 however, and the stubble plowed up and killed. This means, of 

 course, that carefully selected seed must be imported, for replanting. 

 Fortunately there is still an abundance of healthy stock in Louisiana 

 and other cane sections in the United States. As a result of its 

 recent exhaustive survey for mosiac disease, the Office of Sugar- 

 Plant Investigations of the Bureau of Plant Industry is in a position 

 to furnish information on the nearest or most accessible source of 

 clean seed for any region. Data have been secured on the prevalence 

 of other diseases and insect pests in all cane regions, so that reason- 

 able security against the dissemination of other cane maladies is 

 assured. 



EXCLUSION. 



There are at the present time (October, 1919) a number of large 

 cane areas in the United States not yet invaded by the mosaic 

 disease. Cane planters in these areas should urge the enactment of 



