It is common to use adjuvant/surfactants mixed with herbicides. These products, sometimes call spreader-stickers, increase the success of the treatment. They do this by improved penetration, increasing coverage, and extra absorption on the plants being sprayed. Some common brand names are R-11, R-900 and Sylgard 309.
If there are any questions about the use of a chemical product, please call your local weed control agency for instructions.