SECTION" H. — NATURE OF THE " BMfillT." 29 



Leaf Spots. Spots in the leaves of canes are produced in Trinidad 

 by two fungus diseases, the Ring-spot disease {Leptnsphaeria aacchari) 

 and the Eye-spot disease {Helminthosporium sacchnri). Both 

 of these are readily distinguishable from the streaks caused by frog- 

 hopper injury, by their size and shape. The spots produced by Ring- 

 spot start as a small purplish red discoloration which later turns brown 

 inside but spreads equally in all directions, remaining more or less 

 ro una and very seldom reaching half an inch in length "in the direction 

 of the leaf axis (Plate II. Fig. 2). It is usually commonest in the 

 ■ outer half of the older leaves. 



The "Eye-spot" streaks (Plate II. Fig. 3) are a dark brownish red 

 in colour, elongated in the direction of the axis, usually small and closely 

 crowded on the leaf, where they may join up to form larger irregular 

 streaks. They also start almost from the first as a discoloured area. 

 They may be found developing on leaves which have only just unrolled 

 and in severe attacks cause a browning of all the leaves which at a dis- 

 tance resembles that produced by froghoppers, but is of a deeper reddish 

 colour. Up to the present this disease has only been found on one 

 cane, D. 109, in certain small areas, and seldom appears before the 

 month of December when all froghopper injury has ceased in 

 normal years. 



Mosaic Disease or Mottle Leaf. A. serious cane disease of unknown 

 cause in Porto Rico, Louisiana and elsewhere, results in the more or less 

 distinct mottling of the blade of the leaf with pale yellowish green spots. 

 This disease has recently been discovered in Trinidad and steps are 

 being taken to prevent its spread. There should however be no 

 confusion between this and the froghopper blight as the leaf markings 

 are quite different in colour (never darker than the healthy leaf) and in 

 shape and distribution. 



Mosaic Disease has been shown in the United States of America, 

 to be transmitted from one plant to another by certain sucking insects. 

 Experiments in Trinidad to test if the froghopper is a carrier have so 

 far given negative results. 



hiscct Borers. Failure of the canes in Trinidad is frequently caused 

 by the damage due to the Large Moth-borer {Castnia liens) and the 

 Small Moth-borer {Diatrcea spp.). The latter is the usual cause of 

 " dead heart," which consists of the death of the centre green leaves of 

 the cane owing to the destruction of the growing point bj^the caterpillar. 

 The lai'ge borer, which is found at the base of the stem is frequently the 

 cause of the failure of the smaller shoots in a stool and should always be 

 sought for before such injury is ascribed to froghopper blight. 



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