Soil samples were used to estimate mean populations of plant-parasitic nematodes in groves of four tropical tree crops in South Florida: guava (Psidium guajava), avocado (Persea americana), mango (Mangifera indica), and 'Tahiti' lime (Citrus x 'Tahiti'). For each nematode-crop combination, relationships were developed between the number of trees to be sampled in a grove and the number of sites to be sampled per tree to maintain a predetermined level of precision (standard error 25% of the mean). Cost functions were used to select the most economical sampling plan from several equally precise alternatives. On Rockdale soils in south Florida the most efficient sampling plan for most parasitic nematode species was to sample a number of trees in the grove at one site per tree, rather than fewer trees at several sites per tree. An exception occurred with Tylenchulus semipenetrans on lime, because of the high variablility in larval population levels at various sites around the same tree. F
