61 



Barh canker. — The fungus causing this disease appears to be 

 Phytophthora Faheri ; there being then two distinct forms of disease 

 apparently caused by different species of the same genus. The 

 fungus was known to cause a canker on Hevea as long ago as 

 1903 in Ceylon. In this country, however, as far as I am awai*e the 

 disease has only recently been found. 



Certainly on estates! visit I Imd not been able to attribute any 

 pathological condition to the fungus Phytophthora until March of 

 this year. The disease starts in patches usually on or near the 

 tapped bark but they may appear at a higher level. It is possible 

 that the first indication may be that the tree ceases to yield latex. 

 If undiscovered at an early stage the decaying tissue will attract 

 borers and the appearance of boring beetles may be the first visible 

 sign. In all cases when latex ceases to flow the bark should be 

 lightly scraped ; if a green layer is found the tree is healthy. 

 Sometimes, in the case of trees with a very scaly outer bark, the 

 green layer is not very obvious. If the tree is attacked by the 

 fungus Phytophthora. Faheri a black layer is found on lightly scraping 

 and the cortex beneath is variously coloured, greyish, brown or dirty 

 red or purple red according to the stage in the attack, i.e., it may be 

 greyish in the early stage or may be very dirty red which changes 

 to purple red on exposure in advanced cases. 



The diseased patch usually has a well-defined dark border. 

 No latex will flow from patches of cankered bark but surrounding 

 bark may yield extraoi'dinary quantities, it must be understood 

 that the colour of the bark only applies to the internal layers of 

 bark and that it can only be detected by scraping away outer layers. 

 Usually there is no external indication of the disease. The disease 

 is capable of spreading and may kill tlie whole bark from the point 

 of attack to the position of origin of fii*st branches or higher or all 

 the bax'k of the main stem. Boinng beetles are attracted by a 

 peculiar smell, which appears to be characteristic of the cankered 

 bark, and they may possibly cause more injury than the canker itself. 



Treatment. — The red canker patches of bai'k canker must be 

 excised or scraped if patches can be found where the disease has not 

 affected the inner tissue to the cambium and the wounds so caused 

 painted with a 20 per cent, solution of brunolinum in water and soft 

 soap and later covered with coal tar. It is useless trying to apply 

 any form of treatment in the case of badly affected trees where 

 boring beetles have made their entxy into tlie wood. These trees 

 should be cut out and burnt. 



As regards the treatment of " black thread disease " or the 

 "bark rot" of the tapping surface I will here indicate methods 

 advised by other economic mycologists in various countries. 



Rutgers and Arens in Java suggest that " tapping be stopped 

 and the cuts treated every five days with a 20 per cent, solution of 



