220 Some Diseases of Plantation Rubber in Malaya 



In Malaya it is likely that the fungus often begins to grow on decayed 

 stumps from which it passes to the rubber trees, the fungus spreading 

 from one tree to another by contact of diseased roots with healthy 

 ones. On some of the older estates in which the disease has been found, 

 however, very few stumps remain and it is likely that there are other 

 means of infection. Some of the old trees affected by Ustulina zonata 

 had been previously attacked by white ants. White ants frequently 

 invade rubber trees attacked by Fomes lignosus and the reverse process 

 may possibly occur in the case of Ustulina zonata. 



It is important that this disease should be dealt with at an early 

 stage although it is then rather liable to be overlooked. If the condition 

 of the bark on one side of the collar of the tree arouses suspicion it 

 should be examined, and if found to be diseased all discoloured tissues 

 should be cut out and burnt and the exposed surfaces tarred; diseased 

 lateral roots should be destroyed unless they are large, when the 

 unhealthy tissues should be excised. If the fungus has penetrated 

 so far into the tree that it would fall if all the affected tissues were 

 cut out, the tree is doomed, but as the fungus spreads only slowly 

 the tree may be kept in tapping until it ceases to yield latex in paying 

 quantities. In order to act on the safe side, infected areas should be 

 isolated by means of trenches. 



7. Botryodiplodia theobromae, Pat. 



After Corticium salmonicolor , this fungus causes the greatest amount 

 of injury to the shoot system of Hevea in Malaya. Botryodiplodia 

 theobromae may enter the tree in several ways : it may invade young 

 shoots killed by Gleosjiorium albo-rubrum or by Phyllosticta ramicola, 

 it may enter branches already attacked by Pink Disease caused by 

 Corticium salmonicolor, or it may act as a wound parasite without 

 association with attack by any other fungus. Whatever the mode of 

 entry, Botryodiplodia theobromae spreads rapidly downwards in the 

 tissues killing the branches and main stem as it proceeds so that the 

 disease is popularly called "die-back." The fungus usually advances 

 faster in the wood than in the bark, though in some trees attacked 

 during 1914 the reverse was apparently the case. 



Petch (10), Richards (l-'), and Bancroft (l) all point out that Botryo- 

 diplodia theobromae often attacks groups of rubber trees simultaneously 

 and the same tendency lias been noted by the writer. Rubber stumps 

 have been affected by the fungus soon after being planted out though 

 it was not possible to determine the manner of infection. 



