A postal survey was conducted among member Institutes to map out the distribution and severity of all the rubber diseases. The survey will also indicate occurrence of new diseases. The results of the survey conducted in early 1990s had been reported during the IRRDB Workshop held in Cochin, India. Since the first survey, there are noticeable changes in the cultivation of rubber especially the introduction of new clones and increase or decrease in rubber areas in several rubber growing countries. The IRRDB carried out another postal survey in 1998. More member Institutes (14) responded to the survey than to the previous survey.

The rubber plant is infected by many diseases. Some of the diseases are common to many countries while certain diseases are restricted to a region or within a few countries only. The severity of the diseases also varied with countries (Table 1). When only severe diseases (i.e. score 5 and above) were considered, 22 diseases were within this category. The diseases which are considered severe in one or many countries are indicated in Table 2.

The diseases severe in more than four countries are Colletotrichum anthracnose, Colletotrichum leaf fall, Oidium leaf fall, Corynespora leaf fall, Black stripe, Pink disease and white root disease. Three diseases i.e. Colletotrichu leaf fall, Black stripe and White root disease were the most widespread and severe. Colletotrichum leaf fall and black stripe were severe in nine countries while white root disease was severe in six countries. Corynespora leaf fall was recorded in ten countries, but was considered severe in five countries. It is important to note that in certain countries it is considered the most severe disease. In Indonesia it was considered as a devastating disease causing severe economic loss.

The survey also indicated that some of the diseases of rubber are confined to one or a few countries only. The diseases in this category are South American leaf blight (Brazil), Armillaria root rot (Africa), and purple root rot (China). Target leaf spot which is a traditional disease in Brazil was recently recorded in Sri Lanka. Periconia leaf disease occurred sporadically in China and Brazil. The nematode, Meloidogyne incognita infected rubber in China, Brazil and India.

The survey also revealed the occurrence of new diseases of rubber. Several new diseases of rubber were recorded. In Brazil, Colletotrichum gloeosporioides was reported to cause a serious disease and Fusarium moniliforme caused a mild disease on the tapping panels. In India, Pythium sclerotium and Curvularia sp are pathogen causing minor diseases on on nursery seedlings. Curvularia leaf spot was also reported in Thailand. Nattrassia mangiferae caused foot canker and sudden wilt in Sri Lanka. The disease which causes sudden wilting of leaves and death of plants is associated with secondary infection of sun scorched collars of seedlings causing elongated cankers.

A virus disease of rubber which is yet to be named was reported in Brazil. The disease was recorded on clones F4512, F4542, CNSAM 8214, CNSAM 8216, CNSAM 8218, IAN 3087, IAN 6158, IAN 717 and Fx 3925. So far the disease did not cause economic losses. The virus disease is transmitted through seeds and grafting. The symptoms of the disease are strongly manifested when the plants experienced temperatures below 22C.