A very promising Fusarium graminearum isolate was evaluated as a potential biocontrol agent for two important submerged aquatic weeds, Egeria densa and E. najas. In previous studies, the fungus showed high control of the species and satisfactory specificity. However, under some conditions, the results were unstable, probably due to abiotic factors affecting the pathogenesis. In order to evaluate the influences of the photoperiod (0; 4; 8 and 12 daily hours of light) and temperature (15 ºC, 20 ºC, 25 ºC, 30 ºC and 35 ºC), studies were carried-out under laboratory conditions in completely randomized plots. The photoperiod effects were evaluated under 25 ºC and pH 7,0. The temperature conditions were evaluated after less than 12 h of photoperiod and pH 7,0. The disease severity was evaluated through a note scale and fresh weight variation. The major severity notes were observed as the photoperiod decreased, especially when less than 8 h, and as the temperature increased, especially above 25 ºC. There were differences in the plants response to the abiotic factors and the disease development. Egeria densa was more damaged by the fungus in high temperatures as compared to E. najas. Egeria densa was more sensitive to the photoperiod.
