so TRINIDAD AND TOBAGO BULLETIN. [XIX. I. 



THE MOSAIC DISEASE OF SUQAR CANE 

 IN TRINIDAD. 



By C. B. Williams, M.A., 

 (Entomologist in charge of Froghopper Investigations.) 



THE MOSAIC DISEASE. 



In various parts of the world a serious disease or group of allied 

 -diseases of sugar cane is known under various names, all based on the 

 typical condition of the leaves of the diseased plants. " Mosaic Disease" 

 " Mottling Disease " or " Yellow Streak " are names in use in different 

 countries. It has been recorded from Java, Argentine, Hawaii, Porto 

 Rico, Cuba and more recently in Louisiana, St. Croix and Jamaica. 



Diseased canes show an irregular streaking of the leaves with 

 yellowish green, paler than the normal healthy colour, most obvious 

 when the leaf is held up to the light. The intensity of the streaking 

 may vary in different varieties of cane and according to the severity 

 of the attack, from a few paler streaks on the normal green background 

 to a condition when only a few streaks of healthy dark green colour 

 remain on an otherwise pale washed-out looking leaf. 



In some countries, and in some varieties of cane, this mottling 

 ■of the leaf is accompanied by a longitudinal cankering of the canes, 

 between the nodes, with light coloured streaks, and a drying up of the 

 canes resulting in a considerable loss of weight. 



The disease seldom kills the infected stool outright but it is reported 

 to become gradually more severe each year the stool is ratooned. 



Nothing is known of the cause of the disease. Neither fungus nor 

 bacteria have been found after considerable search, and it has been 

 suggested that it is due to some organism too small to be seen by the 

 microscope. 



Experiments carried out in Porto Rico indicate that every cutting 

 taken from a diseased plant carries with it the infection, and none x^ro- 

 duce healthy plants. 



In addition the disease is, in some unknown manner,- infectious and 

 gradually spreads from diseased plants to healthy ones in the neighbour- 

 hood. The spread occurs more rapidly at certain times of the year and 

 it is possible that it is due to transmission by son^ie sucking insect. 



In Porto Pdco the disease was fnsb recorded in 1916 and has spread 

 with great rapidity over more than three-quarters of the area under 

 cane. Ten factories in the diseased area are said to have experienced 

 a reduction in out-put averaging nearly 40 percent., while ten factories 

 in the free area in the same period have slightly increased their yield. 



r * Expc riments at "Wasliiugton have now shown that transmi; slon can be effected 

 by_the ct rn aphis. 



