Fusarium oxysporum f. sp. apii (Foa) race 4, which is in F. oxysporum species complex (FOSC) Clade 2, causes a new Fusarium wilt of celery. We compared Foa race 4 with race 2, which causes Fusarium yellows of celery and is in FOSC Clade 3. Optimal temperatures for celery yield are 16 to 18°C. Soil temperatures in California celery production areas can range up to 26°C, and the maximal rate of hyphal extension of Foa races 2 and 4 in culture are 25°C and 28°C, respectively. Here, we compared the effect of temperatures from 16 to 26°C on growth of Foa races 4 and 2 in two celery cultivars: Challenger, which is resistant to Foa race 2 and susceptible to race 4; and Sonora, which is susceptible to both Foa races 2 and 4. Based on linear regressions, as temperature increases, there is an increase in the log of Foa race 4 DNA concentration in celery crowns and in the reduction in plant height. Based on logistic regressions, as temperature increases, the incidence of vascular discoloration increases in celery with either Foa race 2 or 4 infection. In both cultivars, temperatures of 22°C and above resulted in a significantly (α=0.05) greater concentration of Foa race 4 than race 2 in planta. The concentration of Foa race 2 in crowns in Challenger is temperature-independent and comparatively low; consequently, Challenger is, at least partly, resistant rather than tolerant to Foa race 2.