An evaluation of the potential hazards associated with mutagenicity and acute toxicity of a mycoherbicide formulation based on the fungal pathogen Cercospora piaropi was performed. Neither the mycoherbicide nor any of its components were mutagenic to Salmonella typhimurium TA98 and TA100 with or without metabolic activation. Both the C. piaropi and the mycoherbicide formulation were shown to be moderately toxic with a bacterial bioluminescence assay. No acute toxicity was found in water samples taken from tanks after treatment of water hyacinth with the mycoherbicide.

Microcystis aeruginosa is one of the main harmful bloom-forming cyanobacteria species worldwide. Plant extracts are considered an appropriate practice to obtain effective, economical and sustainable algaecides. For the first time, the effects of Argemone mexicana, Bougainvillea spectabilis, Larrea tridentata and Tradescantia zebrina on the growth of M. aeruginosa in solid and liquid media were investigated by measuring cell density, Chl-a concentration, malondialdehyde (MDA), proteins and nucleotides. Total polyphenol content was quantified to reveal the nature of inhibition. The results in solid medium showed that the methanolic extract of L. tridentata had the greatest effect, showing an inhibition zone of 28.67±0.58 mm. In liquid medium, the methanolic extract of L. tridentata again showed the greatest effects on the cell density of M. aeruginosa (93.80%, p<0.0001), followed by B. spectabilis (87.66%, p<0.0001) and A. mexicana with (87.11%, p<0.001), with EC50 = 13.63, 20.27 and 24.47 mg/L, respectively. L. tridentata also showed a decrease of Chl-a of 91.51% (P<0.0001), MDA increased 6.42 times, and proteins and nucleotides 2.09 and 2.12 times in relation to the control, respectively. L. tridentata showed the highest total polyphenol content, 363.51 mgGAEq/gDE. These results indicate that the decrease in photosynthetic capacity and lipid peroxidation are the most probable mechanisms of action of this species against M. aeruginosa.