20 FKOGUOPPER BLIGHT OF SUGAR-CANE. 



SECTION^ II. 



THE NATURE OF THE "BLIGHT." 



GENERAL SYMPTOMS. 



The name "Blight" is sometimes used in Trinidad, as in other 

 countries, to describe the insect, in this case the froghopper, supposed to 

 be the cause of the damage. Thus one hears that '■ Ph-ht was present, 

 but no visible damage has been caused." In the present report, the word 

 is used in its strict sense to mean the diseased condition produced in 

 the cane. 



Signs of the disease first appear in the cane fields six weeks to twa 

 months after the beginning of the wet season, seldom, if ever, before 

 the middle of June and usually not until the middle of July. The 

 first indication is a slight holding up of the growth of the canes, which 

 cease to make their former good progress.. A. little later the tips of the 

 leaves wilt slightly and unnaturally, especially during the hot part of the 

 day, and narrow reddish-brown streaks begin to appear on their surface. 

 A close examination at this time will reveal the njmph froghoppcrs in 

 their froth on the roots (Plate III) and adults sitting during the day 

 time in the axils of the upper leaves well hidden away. The streaks on 

 the leaves increase in number and size, particularly on the outer leaves 

 of the cane, and the whole plant appears from a distance to have a dead 

 brown colour, frequently described as " as if damaged by fire."' The 

 diseased stools have nearly always a poor root system and are loose in 

 the ground and easily pulled xip. while the old leaf sheaths are frequenth" 

 matted to the stem by various species of fungi. How far this condition 

 can be considered as a consequence, or alternately, as a predisposing 

 cause of infestation is discussed later. 



The browning of the leaves is caused by the sucking of the adult frog- 

 hopper, and the damage to the roots by the combined effect of the 

 nymph and various fungi. The relative pai't plaj'ed b^- each in the final 

 damage to the cane is discussed in Section IX. 



As the older leaves dry up and die the adult froghoppers crowd moi-e 

 and more into the remaining inner leaves, which in turn may be 

 destroyed, and as a consequence all except the largest shoots of the 

 tools die off and decay (Plates IV. to VI.) 



Usually however, the first attack of the year does not reach this 

 state of extreme severity and, as the brood jjasses the canes throw out 

 fresh health}- leaves which gradually replace the damaged ones and 

 normal growth is once more resumed. 



After an interval of about two months a second attack may occur, 

 usually, but not always, of greater seveiitj', and after another period of 

 recovery, a third attack maj' develoii after about the same interval. 



Recovery from all these depends chiefly on the original severity of 

 the attack, on the general conditions of the cultivation, on the variety 

 of the cane, and on the weather conditions prevailing at the time. 



DAMAGE TO THE LEAVES. 

 Apart from the slight wilting and curling which are usually the first 

 signs of blight, the main damage to the leaves is caused by the spread 

 of injury from the points at which the adult fi-oghoppers have inserted 

 their mouth tube to suck out the sap. 



For convenience of reference I have divided the development of one 

 cifthese aieas of injury into four stages. 



