1919.\ INVESTIGATION OF FROGHOPPEB PEST, <£c. 59 



familiar, in the absence of the froghopper and often in the absence of 

 notable insect injury of any kind. 



7. It is the first necessity of success in meeting the various aspects 

 of blight that a closer discrimination should be applied to the estimation 

 of the causes which in any particular case produce it. For this reason 

 the concentration of attention in recent years on the purely entomolo- 

 gical aspect of the subject, while it has so far failed to bring the hoped-for 

 relief, has delayed progress in more promising directions. 



8. It is the main object of the present report to contribute to the 

 understanding of the widespread type of failure of the cane crop to 

 which the non-committal name of blight is the best to apply. It ranges, 

 in the examples exhibited to me, from a condition in which whole 

 fields contain nothing but stunted and worthless stools, the cultivation 

 of which has been abandoned, to merely unhealthy fields which will 

 give, in various degrees, reduced returns. There is another type in 

 which the appearance of health is maintained, but development has at 

 some stage been so arrested that the canes look months younger than 

 they really are. In the definitely unhealthy fields the existence of root 

 disease is general, and its prevalence as a rule appears proportionate to 

 the severity of the damage experienced. 



9. The key to the correct appreciation of root disease is the fact that 

 both its onset and its persistence depend on a condition of weakness or 

 debility in the cane, that is to say the existence of root disease 

 pre-supposes some unfavourable circumstance which enables it to take 

 effect. The list of the possible pre-disposing causes covers all the 

 adverse conditions to which sugar cane is subject, and a complete 

 discussion of the reasons for its prevalence involves a survey of the 

 whole field of cane cultivation. I propose to deal in three sections with 

 the general nature of root disease, the apparent reasons for its epidemic 

 occurrences in Trinidad, and the means which may be adopted for its 

 reduction. 



THE NATURE OF EOOT DISEASE. 



10. The name root disease has come to have specific application in 

 the case of sugar cane to conditions which arise from the invasion of the 

 roots, and in severe cases the underground portions of the stool and the 

 young shoots, by the mycelium of certain fungi which normally exist on 

 the decaying cane material in or about the soil. 



11. The fungi concerned in Trinidad as in other parts of the West 

 Indies are mainly two, or as it would appear to be more accurate to say, 

 two groups, each comprising two or more closely allied species. 



{a.) The Marasmius group. — This is usually represented by 

 Marasmius Sacchari, but the fructifications of other species of Maras- 

 mius are sometimes seen, occurring under conditions at present 

 indistinguishable. The fruiting bodies, which are developed only under 

 very moist conditions, are small papery toad stools usually less than 

 half-an-inch across. They quickly dry up and disappear on a sunny day, 

 and are rarely seen unless specially sought for. The mycelium of 

 Marasjnius Sacchari is more or less distinguishable by the appearance 

 it produces of the leaf sheaths being stuck closely together as if with 

 flour paste. There is no approach to the definite and easily recognisable 

 form pertaining to the group next to be described. 



