Root rot disease of slash pine was further confirmed to be mainly caused by Diphlodia pinea (Desm. ) Kickx. It was also found that Sphaeropsis sapinea (Fr. ) Dyko & Sutton was one of the causal agents. The mentioned 5. sapinea was quite different from the usual D. piuea (synonymy: S. saqinea) in morthology, cultural characters and germination and may be a variety of this species. Inoculation tests showed that both D. pinea and S. sapiuea could make 2-year -old seedlinks as well as 16-year-old weakened uees of slash pine dead, and that the infection of the pathogens was closely related to the defoliation of slash pine caused by Dendrolinus punctatus.