1922.] NOTES ON PROCLAIMED DISEASES AND PESTS. 177 



LITTLE-LEAF DISEASE OF COCONUTS. 



This affection of the coconut pahn is now for the first time proclaimed 

 under the Ordinance. It is common in a scattered way in both Trinidad 

 and Tobago, being often conspicuous on roadside trees. Recently a 

 district was inspected in which the distribution of the disease had 

 assumed epidemic proportions. 



The most obvious character of the disease as seen in these islands is 

 that after its onset the leaves come out smaller and smaller in size 

 until in the end, if no recovery takes place, they are reduced to a 

 ridiculous little crown of aborted stumps not more than l-li feet long, 

 which may be borne at the end of a stem perhaps 20-30 feet high. 



Examination of the central shoot and bud reveals the young 

 leaves with brown necrosed spots and patches on the folded leaflets and 

 on the surface of the leaf-stalk. As the leaves expand the leaf-stalks 

 develop a russeted or corky surface, which later becomes hard and 

 woody, more or less raised and mis-shapen and exhibits well marked 

 cracks. The unyielding nature of the leaves so affected causes those 

 which follow to be more and more severely deformed, and in the later 

 stages the leaflets either do not expand or are almost entirely aborted, 

 and the rachis or mid-rib itself is reduced to a pointed stump. 



Trees of all ages are liable to be affected. Oases are fairly common 

 in fields of young trees, and even very old trees are subject to attack. 

 Conditions in respect of soil and moisture appear to have little influence. 



Affected trees occasionally show some degree of recovery, but this is 

 usually intermittent and the end result in nearly all untreated cases is 

 death. 



The causation of the disease is now under investigation. In the first 

 trace of the lesions, found among the embryonic leaves of the bud, a 

 species of yeast is conspicuous, accompanied, in some cases at least, 

 by a rod-like bacterium. 



The disease is one which responds readily to treatment, even at an 

 advanced stage. A method adopted with complete success is to relieve 

 the constriction of the central part of the shoot by slitting the strainers 

 and forcing the leaves apart, and then pouring a disinfectant fluid into 

 the heart. Tobacco juice is very effective, and apparently any of the 

 ordinary commercial disinfectants such as Jeye's or Kreso, if applied in 

 ■weak solutions that will not seriously burn the tissues, serve the purpose 

 very well. 



MOSAIC DISEASE OF SUGAR-CANE. 



The Mosaic diseases form a peculiar and well-marked group of highly 

 infectious diseases affecting in each instance closely related plants. 

 There are well known mosaic diseases of tomato, tobacco, and Irish 

 potato. The name has reference to the irregularity of distribution of 

 the green colour of the leaves which is the most obvious character of 

 this class of affection. No causative organism can be detected in these 

 diseases, but the juice in all cases conveys infection, often with great 

 readiness. 



