10 TBINIDAD AND TOBAGO BULLETIN. [XIX. 1.. 



19. There is a field of first ratoons at present under observation 

 attacked by this severer form of the disease when the canes were 

 already well-grown and large, which seems likely to be practically 

 destroyed. In this case there was distinct injury to the leaves by 

 froghoppeifs in August and again in October. The field would be known 

 locally as blighted, but the real cause of the injury, as shown by its 

 nature, is the root fungus infestation. 



20. It now appears that the prevalence of root disease over wide 

 areas in Trinidad late in the season, reported on last year by one of us 

 (W.N.), is largely due to the weakening of resistance by previous 

 attacks of froghopper. 



21. The effect of root disease accompan^dng or following froghopper 

 injury is to increase its effects and to prevent recovery, making the 

 blighted condition permanent. 



III. CONTROL. 



22. No direct method for control of the froghopper is at present in 

 sight. Natural enemies, especially the fungus diseases of the adults, 

 exercise a considerable measure of control under favourable conditions. 



23. Root disease can be controlled by reducing the ratooning period, 

 by improving preparation, cultivation and drainage, by the use of 

 organic manures and of lime, and by rotation of crops. 



24. The general evidence goes to show that it is in the fields which 

 have had least attention in these matters and in fields naturally poor 

 that the froghopper finds the most suitable conditions for rapi 

 multiplication. 



25. The admitted exceptions occurring in froghopper years, in which 

 some good fields may be attacked, may very well be due to migrations 

 of the pest from fields in worse condition. 



26. The practice of throwing out fields to grass, especially when 

 the old stools are left to sprout, is definitely bad with reference to both 

 froghopper and root disease, (as well as all other insect and fungus 

 diseases of cane). 



27. It should be an invai-iable rule to plough out as soon as possible 

 stools not intended to be cultivated as ratoons. It is highly desirable 

 that in addition to this a cultivated crop not belonging to the grass 

 family should be grown. 



28. It is our conclusion that well-considered application of the 

 measures referred to in paragraph 23 will give the best protection 

 available against the development of froghopper infestations, will greatly 

 reduce the direct effects of such an infestation when it occurs, and will 

 remove the serious contribution now made by root disease to the final 

 condition of blighted fields. 



January, 1920. 



