Rubber trees are subject to attack by a number of fungal diseases. One, the South American leaf disease, effectively bars the commercial production of rubber in its native continent, South America. On the whole insect pests do not pose a serious problem for rubber planters, though they can be destructive in combination with certain diseases. The rubber tree is deciduous, and the new foliage which grows after the 'wintering' period is susceptible to attack by fungi, insects and mites, in combination. In a severe attack, the young leaves are killed and drop off, a process known as secondary leaf fall. The defoliation can be as severe as 50 to 100%, with a consequent reduction in rubber yield of a half.
The most serious diseases of rubber are root diseases which are caused by fungi that attack and eventually kill the roots. The diseases persist in the soil on infected dead roots. Freshly planted rubber trees remain healthy until their roots come into contact with pieces of diseased root. From a few foci of infection, a whole plantation can be destroyed.
Several fungi can attack and damage the tapping panels. The most important is mouldy rot, which first appeared in Malaya in 1916 and in Java in 1920. A potential threat to the world's rubber industry is the South American leaf blight. This attacks wild rubber trees which occur in the tropical forests of Central and South America. Various attempts, such as those by the Ford and Goodyear companies, have been made to establish rubber plantations in these areas. All have been abandoned because of the devastation caused by leaf blight. The disease is a serious potential threat to the Asian rubber plantations.