UC Riverside International Organization of Citrus Virologists Conference Proceedings (1957-2010) Title An Economic Sampling Protocol for Locating Citrus tristeza virus Reservoirs in a Large Area Publication Date
Journal International Organization of Citrus Virologists Conference Proceedings
In citrus-growing areas where the incidence of Citrus tristeza virus (CTV) is low and CTV spread is suspected, a sampling strategy that maximizes limited resources and allows coverage of large areas would be useful to locate CTV reservoirs. We developed a strategy to estimate CTV incidence over a large area by uniformly sub-sampling portions of orchards. Our sampling method was tested in 79 blocks of citrus ranging in size from 2 to 16 ha in Central California. Some knowledge of the CTV
... of the CTV incidence in each field existed from surveys conducted previously. Each orchard was considered as a separate plot. A subplot of 20 rows by 20 trees (400 trees total) or equivalent was selected in the center of each block regardless of the orchard size or planting density. Each subplot was surveyed using the hierarchical sampling (HS) method and the results compared to previous HS or singles surveys conducted over the entire orchard conducted by the Central California Citrus Tristeza Virus Eradication Agency. The subplot HS procedure was effective in finding CTV reservoirs in three small test plots where singles survey indicated virus incidence was 5.3, 5.0 and 0.5%. When tested in the 79 plots, the subplot HS method was successful and reliable at finding CTV only when incidence was >1%. Therefore, caution should be used if this abbreviated HS system is adopted where incidence is extremely low. The best strategy for its use is to survey a large area by the subplot HS method to locate areas of CTV incidence >1%. Once located, these areas can be prioritized for more thorough surveys or other actions.