56 



ROOT DISEASES OP HEVEA AND CLEAN CLEABING. 



By W. N. C. Belgbave, b.a. 



(Acting Mycologist, F.M.8.) 



'' MHE interest taken in root diseases, which had waned with the 

 control of Fomes, has been revived in the last three yeai's by the 

 discovery of VstuUna 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) . 

 Sphaerostilhe repens. 

 Ustulina zonata. 

 Poria hypolateritia. 

 Brown root disease. — Hymenochaste 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 Fomes is generally too far advanced 

 when discovered, for the tree to be saved. The only signs of Fomes 

 attack which show above ground are drying up of latex, "and 

 Avithering of leaves. The chief characteristic of Fomes is the 

 production of external mycelial sti'ands 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 j 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 

 hyph^e 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 ai*e most frequently found on wet 

 low -lying land. They take the form of brackets which may be 



