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

## TL;DR

This study shows that xanthan gum can be used to create a stable herbicide from a water-insoluble plant extract, which works as well as or better than a commercial herbicide on certain plants.

## Contribution

Xanthan gum is demonstrated as an effective vehicle for formulating insoluble natural herbicides, enabling practical application.

## Key findings

- The S. lappa extract with xanthan gum forms a stable, sprayable, shear-thinning viscoelastic system.
- The extract showed herbicidal activity comparable to or better than Dual on four plant species.
- The extract had low inhibitory activity on Sorghum bicolor, indicating selectivity for weed control.

## Abstract

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 Saussurea lappa 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 S. lappa 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 S. lappa extract presented results comparable to or even greater than Dual for Lactuca sativa, Cucumis sativus, Brachiaria decumbens, and Bidens pilosa. However, it showed low inhibitory activity for Sorghum bicolor, highlighting its potential for selective weed control. This work illustrates xanthan gum as an effective vehicle for formulating insoluble natural products and demonstrates that S. lappa extract is a promising candidate for developing novel herbicides.