270 THE RUBBER TREE BOOK 



wood beneath the bark, and cutting away the bark is not always 

 sufficient to eradicate it. 



Canker (Phytophthora Faberi) is another fungal disease 

 which attacks the stems of Hevea. It is much more frequent 

 in Sumatra than in the Federated Malay States. It is more 

 common among Heveas when they have been interplanted with 

 coffee or cacao. Its presence is not so easily recognized as is 

 the case with pink disease or Fomes, and often the first and only 

 indication of disease is that the trees cease to yield latex. The 

 use of the knife is the only remedy, and tar should be well 

 applied to the wounded spot. A deficiency of potassium in the 

 soil is often a contributing cause to such disease as this, and 

 after liberal manuring the trees become almost immune. 



Dieback (Diplodia theobromae) attacks are ascribed to fungi 

 bearing a variety of names. The leading shoots, or branches, 

 of the tree are first affected. From these Diplodia sends its 

 threads down through the larger branches, spreading far beyond 

 the portions apparently affected. Very severe cutting back is 

 necessary when the branches of a tree become attacked, and 

 all wounds should be well tarred over. The bark of trees 

 severely attacked by Diplodia has a blackened, sooty appearance. 



All cuttings from diseased trees should be carefully burned, 

 as otherwise they will become fertile sources of infection. 



Burrs are peculiar excrescences which grow in, or under, 

 the bark of the Heveas. They are not due to fungoid growths, 

 and are not diseases which imperil the health and existence of 

 the tree. Yet they may be extremely annoying and be a great 

 hindrance to tapping operations. As a rule they are quite 

 small at first, but grow and multiply quite rapidly. The use of 

 the pricker is invariably followed by an alarming growth of 

 burrs, which frequently join on to each other, increase in size, 

 and form large swellings round the trunk of the trees. To cut 

 them out is quite a serious operation, and, on old trees origi- 

 nally badly tapped, it often appears almost impossible without 

 sacrificing the tree. Yet if the trees are manured, the soil 

 cultivated, and tapping operations suspended, the growths can 

 often be removed and the bark largely restored. 



These burr growths, however, are not always the result of 

 bad tapping ; they occur quite frequently on young trees which 

 have never been tapped. They are most numerous on old 



