JL919.'\ FBOGHOPPEB BLIGHT OF SUGAB CANE. 55 



Several different types of damage are possible: — 

 (1.) Caused by Froghopper alone. 

 (2.) Caused by Root Fungi alone. 



(3.) Eoot Disease followed by independent Froghopper attack. 

 (4.) Froghopper followed by independent Root Fungi. 

 (5.) Froghopper attack resulting in increase of Root Fungi. 

 (6.1 Root Disease resulting in increase of Froghoppers. 



1. We have at present no direct experimental evidence that Frog- 

 hoppers alone can cause blight. Several innoculation experiments have 

 been tried by various experimenters but all gave negative results, except 

 one in which conditions resembling blight were produced in potted 

 Para grass by a heavy infestation of froghoppers. (Heriot. Proc. Agr. 

 Soc. VITI. 1908. 550). 



There is also still some doubt as to whether it is the nymph or the 

 adult which is the more dangerous. Experiments to test these points 

 will be carried out this season. 



In spite of this lack of experimental proof, thero is, however, no 

 •doubt that Froghoppers alone, in sufficient numbers, can cause great 

 damage. The severe loss occasioned to plant-canes in years of heavy 

 blight must be due almost entirely to the Froghopper, as root fungi are 

 seldom found in any quantity in canes during their first year of growth. 

 In such cases, as Mr. Nowell has pointed out in his report, recovery is 

 more rapid than when the situation is complicated by the presence of 

 root fungi. 



In addition we know that conditions similar to blight can be produced 

 in other crop'^ (e.g. grass and corn) and in other countries (Colombia, 

 Cuba, British Guiana, &c.) in constant association with Froghoppers. 



2. Damage due to the root fungi alone is sufficiently well established 

 to need little comment. One of the features of such an attack is its 

 close dependence on external conditions such as the rainfall, soil, and 

 general health of the plants, and such a dependence is very noticeable 

 in many of the Trinidad outbreaks. 



3-6. Tn nearly all the cases of blight in Trinidad both Froghopper 

 and root fungi are present and it becomes the question to decide whether 

 either one of them is responsible for the presence of the other, which is 

 the cause of the greater part of the damage, and which can be most 

 •easily reduced. 



In the limits of the present preliminary report the evidence for and 

 against these various conditions cannot be detailed, but after two years 

 observations in the field I am inclined to think that the most usual 

 condition is No. 5 — that is an attack of P\-oghopper followed by, and at 

 least partly responsible for, an attack of root disease. After the 

 Frogho))pers have died out the root fungi persist and may cause the 

 damage to increase out of all proportion to the number of Froghoppers 

 originally present. 



This persistence of the damage after the Froghoppers have disappeared 

 is a very marked feature of many of the attacks of bliglit in Trinidad and 

 is one of the strongest arguments that the insect alone is not responsible 

 for all the damage. 



