DISEASES OF SUGAR CANE 317 



there, but is more common in the hills, where the moisture is 

 greater. It is not uncommon in some districts in Barbados, 

 is reported as very common in Porto Rico, and has been recorded 

 from St. Lucia, St. Croix, and Trinidad. The fungus is very 

 generally distributed through the islands and no doubt occurs at 

 times on sugar-cane in all of them, but it nowhere attracts much 

 attention. 



Causative Fungus. 



The fungus to which the disease is due produces an orange 

 or brick-red discoloration of the leaf-sheaths, often on young 

 shoots. It is distinguished by a copious white radiating my- 

 celimn, on which occur as it matures large numbers of white 

 to brown spherical sclerotia like small seeds. The fungus has 

 been shown by cross inoculations to be identical with Sclerotium 

 Rolfsii Sacc. described under the heading General Diseases. 



Nature of the Attack. 



There is no doubt as to the parasitism of the fungus. The 

 mycelium spreads over the surface and penetrates the tissues 

 of the leaf-sheath by way of the stomata. On young shoots 

 the leaves and even the stem may be more or less affected. 

 Infection apparently always proceeds in the initial stage from the 

 soil, where it is assumed to be carried over by the resistant 

 sclerotia. 



Effects. 



The extent of the damage caused by the fungus on sugar-cane 

 is uncertain. Some planters attribute considerable importance 

 to its presence on young shoots, which are dwarfed and reduced 

 in vitality by its attack. On the other hand it is reported from 

 Porto Rico that in one instance careful observation for six 

 months of a field in which it was growing vigorously owing to 

 the wetness of the season revealed no visible difference in the 

 condition of infested and uninfested stools. The fungus develops 

 only under moist conditions. 



Red Spot of the Leaf-sheath. 



This is the most general of the diseases attacking sugar-cane 

 in the West Indies. In many districts it is difficult to find a 

 shoot which does not show more or less evidence of its presence. 

 It occupies a similar position in Java. 



The affection appears on the outer leaf-sheaths as a large 

 bright red patch, commonly somewhat oval in shape, but ill- 

 defined, with a dark brown spot of dead tissue in its centre. 

 Under this spot, by pulling off the successive leaf-sheaths, one 

 may trace the infection inwards, in the form of red spots which 

 are smaller and smaller until only a red dot appears at the 



