Disease of Rubber caused by Ustulina Zonata. 163 
occurs in the case of Ustulina zovata. We have, however, much 
to learn yet about the methods by which root parasites enter their 
hosts. 
The disease of the collar and root system of rubber trees 
caused by Ustulina zonata is by no means easy to distinguish in the 
early stages when there is some chance of dealing with it effectively, 
yet it is important that this should be attempted, as it is almost 
impossible to save the trees once the disease has made considerable 
progress. If the condition of the hark on one side of the collar of 
a tree arouses suspicion it should he 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 he destroyed, 
unless they are large when the unhealthy tissue should he 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 and 
efforts to save it will probably be useless; since, however, the 
fungus spreads but slowly, the tree may be kept in tapping until 
the end. Such trees should be cut out when they cease to yield 
latex in paying quantities. Although no external mycelium has yet 
been found around trees affected by this disease, it would be acting 
on the safe side to isolate an infected area by means of a trench. 
The fungus probably spreads from one rubber tree to another 
chiefly by contact of diseased roots against healthy ones. 
With the drastic thinning out which has been recently carried 
out on many estates and with the thinner planting of new areas 
than was formerly customary, it is important to remember that 
once the number of trees per acre falls below 80 to 100, the loss of 
a tree is a more serious matter than when an acre carried 150 to 
200 trees. The smaller the number of trees remaining per acre 
the greater must be the attention paid in watching for the appear¬ 
ance of disease and treating it in the earliest stages, otherwise the 
yield from the estate will become seriously reduced. The disease 
caused by Ustulina zonata is a particularly insidious one, and rubber 
planters should be on their guard against it. 
Summary. 
1. A disease of plantation rubber trees caused by Ustulina 
zonata and not hitherto recorded in Malaya is described. It is readily 
distinguishable from the root diseases caused by Fotnes semitostus 
(Fomes lignosus), Sphcerostilbe repens , and Hymenochcete noxia. 
