Spatial Variability of Orange Spotting Disease in Oil Palm

Orange Spotting (OS) disease which is caused by Cadang-Cadang Coconut Viroid (CCCVd) is an emerging problem in oil palm. This study was aimed at quantifying the spatial variability of OS disease severity as an effort to augment the effectiveness of OS phytopathometry appraisal. A 4.2 ha study plot was established in a commercial oil palm plantation at Sungai Buloh, Selangor. A total of 587 geo-referenced trees were visually observed for OS disease symptoms. OS disease severity data were first subjected to exploratory analysis and followed by variography and interpolation analyses to assess spatial variability. The incidence OS disease in the study area was 74.3%. Measured OS disease severity ranged from 0-92.3%. The spatial structure of OS disease severity was described by an exponential model with an effective range of 29.1 m. OS disease severity exhibited a strong spatial dependence with a nugget to sill ratio of 0.15. The spatial variability map of OS disease severity revealed spatial clustering of kriged values, where 73% of the study area showed low severity (1-30%), 25% showed moderate severity (30-60%) and approximately 2% showed high severity (> 60%). This study demonstrates the utility of geo-spatial information in understanding the OS disease severity scale which could assist in site-specific disease monitoring and intervention.