A survey of land for Weligama coconut leaf wilt disease affected palms outside the declared boundary in the Southern Province
After the identification of the Weligama Coconut Leaf Wilt Disease (WCLWD) in 2006, a three km wide boundary zone was declared which stretched from Galle to Tangalle. All suspicious palms recorded within the boundary zone were removed. Gradual removal of affected palms in the core area was also continued. These actions along with many other precautionary steps were taken with the objective to prevent the spread of the disease further beyond the demarcated boundary. After taking continued precautionary measures for more than 7 years, it was timely to find out the presence of any disease affected palms beyond the boundary. Therefore, a sample survey was conducted along a 4 km wide belt beyond the boundary. Uniform sampling locations were ensured by selecting sample sites on a I km grid drawn on the areal image of the area. Each grid covered an area of I km2 (100 ha) Four sampling locations/plots of approximately I ha in extent were selected within each grid. All coconut palms within selected plots were examined for morphological symptoms of the WCLWD and necessary information was recorded. The total area covered by the sample survey was about 40,000 ha and the extent closely examined was about 1600 ha, which was approximately 4% of the total land area covered by the survey. The results revealed that the precautionary measures taken by relevant authorities to prevent the spread of the WCLWD have had a significant effect in containing the disease within the demarcated area. However, some spread of the disease beyond the boundary was detected in a few places within the four km belt beyond the boundary. Thus altogether 18 affected palms were identified in 10 plots in Galle and Malara districts. They were in Akmeemana, Imaduwa and Yakkalamulla DSD in Galle district and Kamburupitiya and Mulatiyana DSD in Malara district. Most of those locations were adjacent to the boundary. However, any detection of even a few affected palms outside the boundary in a sample survey indicates the possibility of having such palms elsewhere in the study area. A comprehensive palm to palm survey is needed for precise detection of such palms. Considering the impending threat from the disease, a palm to palm survey at least within a 4 km belt outside the boundary is suggested to effectively prevent the spread of the disease, despite the cost and the man power required for such an operation.