Recent trends in disease occurrence in the non-traditional rubber-growing areas of Sri Lanka

As the rubber industry is being extended to non-traditional areas in Uva, Northern and Eastern provinces in Sri Lanka, it was important to extend the crop protection arm to those areas also. The disease profile recorded in those areas for a period of three years was studied. The symptomatology of the major diseases and the diversity of the Sri Lankan populations of the pathogens causing major diseases were also studied. Furthermore, the alternative hosts of the pathogens of the major diseases were also looked for. With the observations made, it could be concluded that, during the study period, brown root disease was the malady with the highest incidence in the non-traditional rubber-growing areas of Sri Lanka. Encrustation of sand and stones on the root surface could be identified as the characteristic diagnostic symptom of the disease. The different isolates of Phellinus noxius showed variations in colony morphology. With the contextual observations of the reported incidences, drier soil conditions, poor land preparation and association with the forest-associated tree species were suggested to be the major reasons for the higher incidence of brown root disease in the studied areas. White root disease was also recorded to a lesser extent. Corynespora leaf fall disease was found to be the foliar disease with the highest incidence. Cow pea (Vigna unguiculata) and soy bean (Glycine max) were recorded to be two alternative hosts of Corynespora-causing fungus.