TY  - BOOK
AU  - Nugawela, A. 
AU  - Wijesuriya, W.
TI  - Severity of circular leaf spot disease (CLSD) and impact on latex production and its determinants in wet and intermediate climatic zones in Sri Lanka
PB  - Proceedings of the IRRDB International Rubber Conference 2023, 20-21 February 2023, IRRDB, Kuala Lumpur, Malaysia, pp. 167-173.
KW  - Circular leaf spot disease
KW  - Disease severity index
KW  - Rubber yield
KW  - Dry rubber content
KW  - Latex volume
N2  - Among many other factors, leaf diseases lead to lower productivity and high production cost threatening the economic viability of rubber cultivation. Circular Leaf Spot Disease (CLSD) has been identified as an economically important leaf disease in rubber cultivation. The objective of this study was to identify the impacts of the plantation age, clone and climate condition on the severity of the disease and to ascertain the impact of CLSD on rubber production. The data were gathered from three rubber plantations in the low country wet zone and one plantation in the low country intermediate zone. Yield achieved and its determinants including the Disease Severity Index (DSI) calculated employing canopy characteristics were studied to assess the impact of the disease on the latex yield. Relationship of DSI with Dry Rubber Content (DRC) and latex volume were also studied. In the intermediate zone, the DSI observed was in the range of 0-12% indicating very low incidence compared to the wet zone with DSI ranging from 20-80%. The clone effect on DSI was not statistically significant indicating that all clones including mixed clone vegetations are susceptible for the new disease. Further, it is evident that disease severity increases with the age of the plantations. In plantations, DSI and DRC did not show any relationship, whilst DSI and the latex volume exhibits a negative significant relationship (r=0.241, P=0.0013). The yield percentage achieved against the budgeted was determined by DSI. Harvesters percentage against budgeted and DSI negatively impacts the latex production in rubber cultivations. According to the established relationship with no limitation of harvesters, viz, when 100% of the budgeted harvesters were used, the percent yield achieved against the budget is significantly influenced by the DSI. Under this scenario, when DSI is increased by 10%, the percent yield achieved against the budget is decreased by 2.3 percent. Thus it is evident that secondary leaf fall caused by CLSD leads to significant reduction in crop production, and subsequently increased cost of production which negatively affect the sustainability of rubber cultivations. Latex volume is an early indicator to identify stress caused by a CLSD affected tree
ER  -