Aims: To determine the effect of water activity (aw =0 Æ880–0Æ960) and temperature (15–35C) on the percentage of viable conidia and mycelial growth of three biocontrol agents effective against water hyacinth in Mali: Alternaria sp. isolate Mlb684, Fusarium sacchari isolate Mln799 and Cadophora malorum isolate Mln715. Methods and Results: The fungi were grown in vitro on plates containing potato dextrose agar medium at different aw values (glycerol being added to adjust the aw). The percentage of viable conidia and radial growth rate decreased with decreasing water activity. Statistical analysis showed a significant effect of aw, temperature and the aw · temperature interaction on mycelial growth (P