1921.] FROGHOPPEB BLIGHT IN THISIDAD. 53 



much greater tlian that of their hosts. In Panama a few specimens of 

 a new egg-parasite were obtained but they died before any attempt could 

 be made to breed them. la .July 1917, owing to tlie great difficulty of 

 carrying on the work single-handed and with the prevailing conditions of 

 transport, I returned to Trinidad to study the pest in the island. 



In 1918 and 1919. Nowell emphasized the relation between local 

 infestations and the condition of the soil, and advocated the application 

 of agricultural methods to the reduction of blight. 



THE NATURE OF THE BLIGHT. 



Damage usually' first appears six weeks to two months after the 

 beginning of the wet season and tlie canes stop growing, and the leaves 

 wilt and are streaked with brown marks. After some weeks recovery 

 sets in, usually to be followed by a second and occasionally a third attack 

 at intervals of about two months. 



From each puncture of the adult froghopper on the leaf an elongated 

 area of injury spreads, at first pale and later brown. Incrjase in size 

 of this spot may continue for as long as four or five weeks and, from 

 an almost imperceptible point, the damaged area mxy reach five inches 

 in lengtli and a quarter of an inch in width forming a long discoloured 

 streak on the leaf. The centre of this area finally dies completely 

 If these streaks are numerous they may join up to form large 

 dead areas on the leaf. It follows that the injury to the leaf, and so to 

 the plant, may continue to increase after the brood of froghoppers has 

 passed. 



The stem is only indirectly damaged by loss of food from the 

 damaged roots and leaves. The growing point is frequently stained 

 with red internally, especially at the young nodes ; small pockets of 

 gum are sometimes found, and an itnnatural brittleness frequently 

 causes the cane to break off just above one of the upper nodes. The 

 internodes or joints which should be increasing in length and width, 

 remain shorter and thinner than usual and harden while still in this 

 condition, recording on the growing cane the check that the plant has 

 received. Thus from the lengths and widths of successive internodes on 

 a fully grown cane past attacks can be determined. The shortening 

 of the upper internodes causes the leaves to be crowded together 

 in a fan-like arrangement. In addition the eyes near the top of tlie 

 cane frequently send out shoots, and adventitious I'oots are developed 

 from the joints near the ground. 



The roots ai*e damaged both by the sucking of the nymph, by the 

 root fungi usually associated with blight, and by the unfavourable soil 

 conditions nearly always found in fields liable to attack. The root 

 system is poor and the plant can be pulled from the ground with com- 

 parative ease. 



The blighted canes contain less sap than health.y ones, but often a 

 higher sucrose percentage. The sucrose is said to be more easily 

 inverted in sap from diseased canes, and the sap is frequently acid. 



The different parts of the stool are usually damaged inversely as 

 their size and vigour. The smallest shoots are killed, the medium sized 

 ones severely checked, and the larger only slightly injured except in 

 cases of sey,ere continued damage. 



