104 FUOGllOPPKR BLIGHT OF SUGAR-CANE. 



Fredliolm (1912 B. p. 416) discussing the serious drought at the 

 beginning of 1912, and the outbreak of blight which followed it, writes 

 "That there is a connection between these two occurrences there is not 



the slightest doubt in my mind The frequent and widespread forest 



and field fires of the drought may be contributory reasons for the 

 increase of the froghopper. Many of the natural enemies, which under 

 normal conditions would tend to keep this pest down, must have perished 

 in the field fires. Vast numbers of snakes, lizards, toads and frogs must 

 have iDerished in the field fires. The eggs of the two first mentioned 

 must have been destroyed by tens of thousands. Ponds and marshes 

 ■drying up would entail the destruction of nearly all the eggs of the latter 

 and their tadpoles." 



It is however probably on the Green Muscardine fungus that the 

 ■dry weather has the most important effect. This fungus can only grow 

 well in a moist atmosphere. Attempts to produce artificial infection of 

 adult froghoppers during the dry season failed until the cage was 

 surrounded by damp cloth to produce a moisture-laden atmosphere. 

 Dry weather at the time of the second brood of froghoppers will prevent 

 the rapid spread of this disease, (which under favourable conditions may 

 destroy the greater part of the brood), and as a result the following third 

 brood will be much more serious. Very heavy downpours may also 

 produce a similar effect by washing to the ground many spores that 

 might otherwise have come into contact with the adult froghoppers. 



We know that both dry v/eather and heavy downpours are correlated 

 Avith blight and this is undoubtedly one of the ways in which the effect 

 is produced. 



Dry weather has probably a similar effect on the Empusa fungus, but 

 this is usually so rare that its reduction would be little felt. 



(3) Direct effect on the Cane. 



Dry weather during the growing season reduces the vitality of the 

 cane, checks growth, and puts it in a condition in which it is more 

 likely to succumb to injury, or if the injury is already present it 

 prevents recovery. This is one of the effects of the severe Indian 

 Summer. 



Further experiments are needed to see if the spread of the leaf 

 injui-y from the point of puncture of the froghopper is more rapid in dry 

 weather than in wet. A few observations I have made seem to indicate 

 this, but no opportunity has yet occun'ed to follow up the investigation. 



(4) Indirect effect on the Cane. 



Severe injury by root fungi is in many countries correlated with 

 unusually dry weather. The main physiological effect of the presence of 

 root fungi is to increase the severity of the injury that would be caused 

 by the lack of water. 



The importance of rainfall in connection with root disease is well 

 illustrated in Barbados, where in the dryer areas only a single crop can 

 be obtained from one planting, whereas two or even three can be cut 

 further inland where the rainfall is higher. This is largely due to the 

 rapid increase of root fungus in the dryer areas when any attempt is 

 made to gi-ow ratoon canes. 



