Maybe a dispensing system which more selectively targets the weeds should instead of using less killer, use a less effective killer. Instead of some clever bit

Maybe a dispensing system which more selectively targets the weeds should instead of using less killer, use a less effective killer. Instead of some clever bit of selective plant killing molecular wizardry, just spray the weed with lye (NaOH). Dissolve the weed and any overspray or residual will lightly raise the pH of the soil. If you have alkaline soil problems, then maybe use sulphuric acid instead.