Interactions between a sulfonylurea herbicide and Brij35 and Zonyl FSN 100 micelles

The use of an adjuvant agent can strongly improve the biological activity of many herbicides, reducing their application rates to the lowest effective level. Vegetal and mineral oils1, for example, enhance the penetration of post-emergence herbicides into the plant2,3. Surfactant are the most widely used adjuvant agents, because they can induce the absorption of the herbicide by changing the viscosity and crystalline structure of waxes on leaf and stem surface4. The formation of micelles of the non ionic surfactants Brij 35 and Zonyl FSN 100 allowed a dose reduction of the post-emergence sulfonylurea herbicide Triflusulfuron Methyl (TFSM), against some weeds such as Serratia faberi. The interactions between the TFSM and the two surfactants have been investigated. The binding constants between the sulfonylurea herbicide and Brij 35 or Zonyl FSN 100 have been fluorimetrically measured at 25°C in aqueous solution at pH 2.0. The cmc and the aggregation number of the surfactants have been calculated in the presence and in the absence of TFSM by determining the surface tension and the polarity changes of the Brij 35 or Zonyl FSN 100 aqueous solutions. The cmc and the aggregation number of both the surfactants are not affected by the presence of the herbicide because the micelles can solubilise the TFSM probably in their polyoxyethylenic corona region. The high binding constant of Zonyl FSN 100 for TFSM may explain the lower efficiency of this surfactant as adjuvant agent for TFSM than Brij35.