The objective of this study was to compare the effect of the fungicides prochloraz and tebuconazole (0-1 µg/ml) on lag phase, growth rate, and T-2 + HT-2 toxin production by strains of Fusarium sporotrichioides and Fusarium langsethiae on oat-based media under different conditions of water activity (a_w; 0.98 and 0.95) × temperature (15 and 25 °C). Relative effective dose values for the fungicides required to inhibit growth by 50% (ED₅₀) and 90% (ED₉₀) and T-2 + HT-2 production were determined. The lag phases prior to growth were prolonged at the marginal a_w × temperature conditions tested and by the presence of the fungicides. The growth rates of F. sporotrichioides and F. langsethiae were similarly inhibited by prochloraz compared with the controls. However, in the presence of tebuconazole, F. langsethiae was much more tolerant with very little inhibitory effects of the fungicide. The ED₅₀ values ranged from 0.08 to ≯1.0 µg/ml for prochloraz and from 0.34 to ≯1.0 µg/ml for tebuconazole in the case of F. sporotrichioides. For F. langsethiae, these values were 0.09 to ≯1.0 and 0.31 to ≯1.0 µg/ml at the two temperatures and a_w levels tested. Prochloraz (0.2-0.4 µg/ml) effectively inhibited toxin production at 15 °C and the two a_w levels examined. However, at 25 °C the fungicide was less effective, regardless of the a_w level. For tebuconazole, there were significant differences in efficacy against the F. sporotrichioides and F. langsethiae strains. The latter species produced consistently higher amounts of T-2 + HT-2 toxin at both 15 and 25 °C and 0.98 a_w. The differential tolerance to the fungicides between the fungal species is discussed in terms of growth and toxin production.