55 
ROOT DISEASES OE HEVEA AND CLEAN CLEARING. 
By W. N. C. Belgrave, b.a. 
{Acting Mycologist , F.M.S.) 
H^HE interest taken in root diseases, which had waned with the 
control of Fames, has been revived in the last three years by the 
discovery of Ustulina and Poria as common and destructive parasites 
of Hevea ; and in some quarters something approaching a panic was 
experienced. 
Still more recently, root diseases have been again overshadowed 
by bark cankers. Without minimizing the seriousness of the latter, 
it is to be urged that root diseases be not neglected — especially now 
that the policy of drastic thinning out has been widely adopted. 
The fungus root diseases known to attack Hevea in Malaya are : 
Fomes lignosus (semitostus ) . 
S'phserostilbe repens. 
TJstulina zonata. n 
Poria hypolateritia. 
Brown root disease . —Hymenorfuete noxia. 
Of these, Fomes lignosus is the only one which regularly attacks 
young rubber. Although described since 1854, it was not till 1904 
that its parasitic nature was recognized — by Ridley. Bancroft fully 
described the fungus and its mode of attack on Hevea in 1912. Like 
all root diseases an attack of Fames is generally too far advanced 
w T hen discovered, for the tree to be saved. The only signs of Fomes 
attack which show above ground are drying up of latex, and 
withering of leaves. The chief characteristic of Fomes is the 
production of external mycelial strands on the diseased roots. 
When young these are white, and much branched, becoming later 
cord-like and brown yellow, or reddish ; and attaining a thickness 
of as much as | inch. The mycelium under favourable conditions is 
capable of growing for short distances though the soil independently 
of roots. The most favourable conditions are moisture and acidity, 
hence in heavy clay or peaty lands, much more unattached 
mycelium will be found, than in looser drier soils. If the 
source from which the mycelium has started be removed, the 
hyphse soon die, and no mycelium can be found after a lapse of 
a few days. It follows that once all the diseased wood has been 
removed from an infected area, there need be no fear of the “ free ” 
mycelium carrying on the disease. 
The fructifications of Fomes are most frequently found on wet 
low-lying land. They take the form of brackets which may be 
