More than a Thickener: Xanthan Gum as a Vehicle for the Herbicidal Extract of Saussurea lappa and Its Rheological Characterization

The increasing demand for food is the driving force behind the search for novel, more selective, and less hazardous agrochemicals. Natural products are gaining prominence recently due to the promise of being green agrochemicals, but many natural products are poorly soluble in water, which reduces their applicability. In this work, we successfully formulated a water-insoluble <i>Saussurea lappa</i> root extract into a stable aqueous suspension using xanthan gum. The colloidal suspension was characterized by rheology, dynamic light scattering, and zeta potential. The results demonstrated that the suspension is a stable, sprayable, shear-thinning viscoelastic system (weak gel). A series of <i>S. lappa</i> solutions with xanthan gum were prepared and tested against five plant species, observing the inhibitory effect on the shoots and roots. The results were also compared with the commercial herbicide Dual. The <i>S. lappa</i> extract presented results comparable to or even greater than Dual for <i>Lactuca sativa</i>, <i>Cucumis sativus</i>, <i>Brachiaria decumbens</i>, and <i>Bidens pilosa</i>. However, it showed low inhibitory activity for <i>Sorghum bicolor</i>, highlighting its potential for selective weed control. This work illustrates xanthan gum as an effective vehicle for formulating insoluble natural products and demonstrates that <i>S. lappa</i> extract is a promising candidate for developing novel herbicides.