174 



THE AGRICULTURAL NEWS. 



May 31, 1919. 



PLANT DISEASES. 



INVESTIGATION OF THE FROGHOPPER 



PKST AND DISEASE OF 



SUGAR-CANE. 



In December 191S, Mr. W. Nowell, Mycologist on the 

 staff of the Imperial Department of Agriculture, visited 

 Trinidad at tte request of the Government of thiit colony for 

 the purpose of making investigations on the prevalence of 

 the froghopper pest, and its relation to disease of the sugar- 

 cane. 



When Mr. Nowell's services were asked fi>r in this 

 connexion, the invistigations which had been in progress for 

 some time had reached a stage when it was felt that factors 

 other than the presence of froghoppers were at work, 

 causing the serious loss of the sugar crop which was com- 

 plained of. Mr. Ncwell's investigations fully confirmed 

 this impression. His report, which it is intended to publish 

 in the pjges of this Journal, will doubtless be of material 

 service to those engaged in the sugar industry of Trinidad, 

 and of interest to cane planters generally. 

 Mr. Nowell writes : — 



' 'I he situation which led to the request for my services 

 1 understand to have arisen as follows : Mr. C B. Williams, 

 Kntomologist-in-Cbarge of Froghopper Investigations, had 

 found that the prevalence in sugar cane fields of the condition 

 known in general terms as blight, in many cases did not 

 correspond with the severity of froghopper infestation. In 

 some cases of severe injury the insect was never present in 

 numbers which appeared to be at all adequate to explain the 

 damage, while in others, froghoppers were present in lartie 

 nuniber.s with much less visible effect on the cane. Mr. 

 Williams reached the conclusion that an additional factor 

 roust be involved in the production of blight, and this he 

 came to believe was root disease of fungoid origin. For this 

 reason he desired the co-operation of a mycologist with 

 experience of the effects of root disease in places where no 

 complications with froghoppers exist. 



' At tlie lime of my arrival in Trinidad the froghopper 

 infeetaiion was practically over for the duration of the 

 current crop, and I nowhere saw more than a scanty and 

 scattered remnant. The period of my visit, which covered 

 the la.st two or three weeks of the wet sea-son and the 

 beginning of the dry, was the most suitable for the estimation 

 of the posiiion held by root disease in the (iiial condition of 

 blighted fields, though it would have been more sntisfactory 

 if I could have approached the subject with personal 

 e.\prience' of the immediate effects of froghopper activity. 

 ' From an early stage in the investigation, and without 

 prejudice to conclusions as to the ability of the froghopper to 

 produce serious damage, it became evident that the name of 

 the insect was in popular use to cover practically all the 

 causes which may operate to produce an unhealthy appearance 

 in standing canes. In many fielis other adverse conditions 

 were present to a degree which 1 should unhesitatingly accept 

 as suilicient to account for depression or failure, without any 

 necil to bring in the froghopper as an agent. Such conditions 

 do in fact, regularly produce similar results in all the islands 

 with which I am familiar, in the absence of the tro^hopper 

 at.d often in the ab.sence of notable insect injury of any kind. 

 'It i" the first necessity of success in meeting the various 

 aspects 01 blight that a closer discrimination should be apjjlied 

 to the estimation of the causes which in any particular case 

 produced it. For this reason, the concentration of attention 

 in recent years on the purely entomological a.specl of th 



subject, while it has so far failed to bring the hoped-for relief, 

 has delayed progress in more promising directions. 



'It is the main object of the ['resent report to contribute 

 to the understanding of the widespread type of failure of the 

 cane crop to which the noncommital name of blight is the 

 best to apply. It r^mges, 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 'ns. There is another type in 

 which the appearance of is maintained, but develop- 



ment has at some stage bi arrested that the canes look 



months younger than thc_) really are. 



'The key to the correct appreciation of root disease is the 

 fact that both its on.set and its persistence depend on a con- 

 dition of weakness or debility in the cane, that i.s to say, the 

 existence of root di.sease pre.-upposes some unfavourable 

 circumstances which enable it to take effect. The list of the 

 possible predisposing causes covers all the adverse condition* 

 to which sugarcane is subject, and a complete discussion of 

 the reasons for its prevalence involves a survey of the whole 

 field of cane cultivation. I propo.se 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. 



TlIK N.VTURE 01'" ROOT DISEASE. 



'The name root disease has come to have specific appli- 

 cation in the case of su^ar-cane to conditions which arise 

 from the invasion of the roots, and in severe cases the un- 

 derground portions of the stool and the young shoots by the 

 mycelium of certain fungi which normally exist on the decay- 

 ing cane material in or about the soil. 



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. 



(<;.) The A/'iirasmua fjrou/'. — This is usually repre- 

 sented by Afarasiii/ii.i Saa/iari, but the fructifications of 

 other species of Marasmius 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 A inch 

 across. They c|uickly dry up and disappeai on a sunny day, 

 and are rarely seen unless specially .sought for. The 

 mycelium of Marasiiiiin Suu/iari is more or less distinguish- 

 able by the appearance it produces of the leaf-sheaths being 

 stuck closely ii>gether as if with Hour paste. There is no 

 approach to the definite and easily recognizable form pertain- 

 ing to the group next to be de.scribed. 



(/<.) The 0,/o//t/a groii^.—k white luyceliuin, easily 

 distinguishable from that of Marasmius by its feaihery 

 pattern of growth and the production of abundant stellate 

 crystals of calcium oxalate, has long been known as apparent- 

 ly capable of producing effects similar to tlio.se of Marasmius. 

 It has been commonly referred to as the stellate crystal 

 fungus, and, as a mycelium of unknown artiuities, was given 

 the name 1/iman/ia s/el/ijfrii by .1. !!• Johnson. Recently 

 Dr. P.urt has <lescribed the fructifications of Odon/ia Sacihari 

 and O. saic/htricola from I'orto lUco material; two closely 

 related funiii which produce their spores on cane trash in a 

 clo.selying, granular, buff culouied layer, hardly distinguishable 

 without the aid of a lens from the surface of the dry trash 

 itself. From the constant as.soci:uion and the apparent 

 organic connexion of Ddonlia fructifications with the typical 

 stellate crystal mycelium, I was led by observations in Trial, 

 dad to believe that the two belonged to tlicsame fungus, and 



