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چکیده
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Abstract BACKGROUND: There is a public interest in developing bio-surfactants due to their low toxicity and high biodegradation potential. However, their biological, surface, and behavior has not been investigated to use with agrochemicals. RESULTS: Critical micelle concentration (CMC) for synthetic surfactant dioctyl sodium sulfosuccinate (DOSS), bio-surfactant rhamnolipid (RL), and bio-surfactant surfactin (SF) were 1200, 50, and 50 mg L-1, respectively. Based on the ability of the surfactants to reduce the surface tension of trifloxysulfuron-sodium spray solution at 0.25 to 1x CMC, they could be ranked: SF > RL > DOSS. While, at 1.5 to 4x CMC, they could be ranked: SF = RL > DOSS. Without surfactant, trifloxysulfuron-sodium at 10.04 g ha-1 controlled johnsongrass up to 50% (ED50). At best, SF at 1 to 4x CMC halved ED50. Unlike DOSS, which increased ED50 (12.89 g ha-1) due to a phytotoxic effect, SF and RL at 4x CMC decreased ED50 (5.19 and 6.50 g ha-1, respectively) without a phytotoxic effect. The 5-µl droplet containing SF dried faster due to the greater spread on the leaf surface than other surfactants. Although the wetted area of the leaf with the droplet containing RL was wider than that of DOSS, it dried later. This observation contradicts the previous theory. CONCLUSION: In terms of dosage, safety, and efficacy, the RL and SF were comparable to DOSS to tank-mix with trifloxysulfuron-sodium. It seems that RL also works as a humectant; SF likely works as a wax solubilisant.
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