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During the growing seasons of 1994-1997, we observed asparagus decline in areas such Mexicali, Caborca and Guanajuato, Mexico, and the Imperial Valley of Southern California. In fields established for five years or more, 40-80% of the plant population showed ground symptoms of chlorosis and growth reduction typical of Fusarium decline. Disease incidence was similar between geographic areas. Of the 32 fields inspected disease incidence range from 78 to 97%. Samples of crowns were taken from fields in each growing area and assayed for Fusarium spp. Isolates of F. proliferatum and F. oxysporum developed on Komada medium. Single spore transfers to PDA (Potato Dextrose Agar) and then to carnation leaf agar were made to establish species identification. On crown samples, F. proliferatum was the dominant species (60-90%) while 5 to 20% of the isolates were F. oxysporum. The two species were differentiated on the presence or absence of chlamydospores and polyphialides. Pathogenicity of both species was established in asparagus seedling using an in vitro spore suspension method. Root lesions and mortality determined the degree of virulence. This study is the first report of F. proliferatum infecting asparagus in Mexico. It is the most prevalent Fusarium specie in the desert growing areas and it is responsible for causing asparagus crown rot and decline in all geographic areas surveyed.