Spreading decline is a severe disease of citrus caused by Radopholus citrophilus that is only encountered on Florida’s central ridge of deep sandy soils. The nematode is commonly called the burrowing nematode because of its extensive tunneling through root tissue as a migratory endoparasite. The disease was first described in 1928 and the causal organism was identified in 1953 (Suit & DuCharme, 1953). The name of the disease is descriptive of the rapid progression of decline in infested groves which can reach 15m/year. The nematode was formerly known as the citrus race of R. similis (Cobb) Thorne, and was distinct from the banana race for which citrus is not a host (DuCharme & Birchfield, 1956). It was renamed as a sibling species to R. similis (formerly the banana race of R. similis) in 1984 based on differences in chromosome number, isozyme patterns, mating behavior and host preference (Huettel et al., 1984); small morphological differences have also been detected (Huettel & Yaegashi. 1988). With the new classification, host preference may become a minor species determinant since a population of R. citrophilus that attacks Anthurium sp. but not citrus has been detected in Hawaii (Huettel et al., 1986). Similarly, a population of R. similis sensu lato with five chromosomes (as does R. citrophilus) for which citrus is not a host was reported from plantain in Puerto Rico (Rivas & Roman, 1985a,b). Because it is presently difficult to identify R. citrophilus with certainty, due to the nature of the several criteria which must be considered, governmental regulatory agencies continue to quarantine “R. similis” as the burrowing nematode without regard to the concepts of races, biotypes, or sibling species (Holdeman, 1986).