Phytotoxicity of 2,4-D and fipronil mixtures to three green manure species.

Sugarcane expansion has been associated with soil contamination by agrochemicals. Pesticides can affect plant growth, and their mixture might have potentiated effects on exposed species. This research aimed to evaluate the influence of fipronil on the phytotoxicity of 2,4-D on three green manure plant species: Canavalia ensiformis , Dolichos lablab , and Lupinus albus . Plants were exposed (for 21 days, at 25 °C) to a control soil and five concentrations of each pesticide and their combinations (36 treatments, considering a full-factorial approach). Effect concentrations of 50% growth inhibition (EC 50 ) were estimated. No phytotoxicity effects were identified when plants were exposed to different fipronil concentrations (up to 0.12 mg kg -1 ). All species exposed to 2,4-D showed a decrease in shoot and root length and fresh/dry biomass. L. albus and D. lablab roots showed the highest sensitivity when exposed to 2,4-D among the endpoints (EC 50 = 0.02 and 0.05 mg kg -1 , respectively), while C. ensiformis roots were the most tolerant (EC 50 = 0.98 mg kg -1 ). However, the interference of fipronil on the toxicity of 2,4-D was not detected in different mixture proportions, indicating no interaction between pesticides. Residues of 2,4-D might also impair other crops' growth, compromise productivity, and limit phytotechnologies for soil recovery.