Sporadic but increasing incidence of two new diseases, which we have named “black-foot disease” and “Phaeoacremonium grapevine decline,” are taking a toll in California's table and wine grape vineyards (Scheck et al 1998a, 1998b). Although the full scope of the problem is not yet measured, grape growers throughout major production regions in California have reported economic losses from replanting costs. Symptoms of these diseases are almost indistinguishable from each other; the diseases are in fact the same that have occurred in grapevines in other places in the world and in older grapevines here. Our research reveals that black-foot is caused by Cylindrocarpon obtusisporum, and grapevine decline is caused by Phaeoacremonium species (P. aleophilum, P. chlamydosporum, or P. inflatipes).